Title:
METHOD AND APPARATUS FOR RECREATING A MUSICAL PERFORMANCE
United States Patent 3604299
Abstract:
A distinct signal is provided throughout the actuation of each control of an instrument, such as during the depression of each key. The relative time occurrences of these performance signals are determined by assigning to each a separate count in a repeated train of gating pulses. The pulse train is produced by a gating means stepped by clock pulses from an oscillator. When coincidence between a performance signal and a corresponding one of the gating pulses is detected, a matrix provides a "key-on" signal to a modulator which is also supplied with the clock pulses. This modulator develops a composite signal or sinusoidal waveform which includes a sync level once every pulse train, a clocking level for every clock pulse during which there is no key-on signal, and a key-on level for every clock pulse during which there is a key-on signal. The waveform may be recorded for later playback or transmitted to a remote location for immediate playback. In playback, the method described above is simply reversed in which the waveform is demultiplexed to provide a plurality of control signals whose presence corresponds to the desired time occurrences of each instrument. By coupling these signals to appropriate drivers, such as relays, the playing mechanisms of the instrument may be actuated to duplicate the original musical performance. Embodiments of the system for use with an organ and for use with a piano are described, as are specific embodiments of the system elements. Modifications to allow operation of a remote keyboard and to provide keyboard transposition and coupling are shown.
US Patent References:
Musical instrument with audio signal to force translator
Percy - July 1965 - 3195389
Device for the successive amplification of a number of low voltages
Klein et al. - October 1965 - 3213290
Synchronous multiplex telegraphy
Normand et al. - August 1967 - 3337687
Method of and apparatus for teaching the operation of a keyboard controlled machine or instrument
Schmoyer - April 1968 - 3377716
Multiplex transmission system including sequenctial pulsing circuitry
Lien - July 1968 - 3395250
Musical instrument with audio signal to force translator
Percy - July 1965 - 3195389
Device for the successive amplification of a number of low voltages
Klein et al. - October 1965 - 3213290
Synchronous multiplex telegraphy
Normand et al. - August 1967 - 3337687
Method of and apparatus for teaching the operation of a keyboard controlled machine or instrument
Schmoyer - April 1968 - 3377716
Multiplex transmission system including sequenctial pulsing circuitry
Lien - July 1968 - 3395250
Application Number:
05/030638
Publication Date:
09/14/1971
Filing Date:
04/22/1970
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
984/303, 984/305, 84/655, 84/341, 346/33R, 84/682, 984/304
International Classes:
G10H1/00; G10F1/00
Field of Search:
84/2-5,470,1.01,1.02,1.28,107,171 178/50-53.1 179/15LL,15AC
US Patent References:
Primary Examiner:
Hirshfield, Milton O.
Assistant Examiner:
Weldon, Ulysses
Claims:
I claim
1. A method for recreating the performance of a musical instrument involving the playing of one or more of a plurality of musical notes and the operating of other controls of the instrument, comprising the steps of:
2. The method as recited in claim 1 wherein said step of time multiplexing further comprises:
3. A method useful in the recreation of a musical performance, comprising the steps of:
4. A method of operating a musical instrument having a plurality of controls in accordance with the composite signal recited in claim 3, comprising the steps of:
5. A method as recited in claim 3 wherein said pulses have a fixed repetition rate and said step of modulating comprises:
6. A method of operating a musical instrument in accordance with the composite signal recited in claim 5, comprising the steps of:
7. A method for recreating a musical performance involving operation of a musical instrument having a plurality of controls, each control providing a distinct musical note or group of notes upon actuation thereof, comprising the steps of:
8. An apparatus for providing an electrical signal, suitable for recording or other transmission, representing a musical performance embodying the time occurrences of actuations of controls of a musical instrument, comprising:
9. In combination with an apparatus for providing an electrical signal as recited in claim 8, an apparatus for recreating the original musical performance, comprising:
10. An apparatus as recited in claim 8 wherein:
11. In combination with an apparatus as recited in claim 10, an apparatus for operating the musical instrument in a recreation of the original musical performance comprising:
12. An apparatus as recited in claim 8 wherein:
13. In combination with an apparatus recited as in claim 12, an apparatus for operating the musical instrument in a recreation of the original musical performance comprising:
14. An apparatus as recited in claim 8 for use with a keyboard instrument whose controls include a plurality of manually operated keys, wherein said sensing means further comprises a pair of electrical contacts coupled to each key and actuated upon depression thereof, a voltage source, and means connecting said voltage source to each of said contact pairs.
15. In combination with the apparatus recited in claim 14, an apparatus for recreating the original musical performance of the instrument comprising:
16. An apparatus as recited in claim 15, further comprising:
17. An apparatus as recited in claim 11 which is adapted to transpose the key signature of the original musical performance upon recreation thereof further comprising:
18. An apparatus such as recited in claim 11 which is adapted to modify the original musical performance upon recreation thereof by simultaneously operating predetermined combinations of the instrument controls, further comprising:
1. A method for recreating the performance of a musical instrument involving the playing of one or more of a plurality of musical notes and the operating of other controls of the instrument, comprising the steps of:
2. The method as recited in claim 1 wherein said step of time multiplexing further comprises:
3. A method useful in the recreation of a musical performance, comprising the steps of:
4. A method of operating a musical instrument having a plurality of controls in accordance with the composite signal recited in claim 3, comprising the steps of:
5. A method as recited in claim 3 wherein said pulses have a fixed repetition rate and said step of modulating comprises:
6. A method of operating a musical instrument in accordance with the composite signal recited in claim 5, comprising the steps of:
7. A method for recreating a musical performance involving operation of a musical instrument having a plurality of controls, each control providing a distinct musical note or group of notes upon actuation thereof, comprising the steps of:
8. An apparatus for providing an electrical signal, suitable for recording or other transmission, representing a musical performance embodying the time occurrences of actuations of controls of a musical instrument, comprising:
9. In combination with an apparatus for providing an electrical signal as recited in claim 8, an apparatus for recreating the original musical performance, comprising:
10. An apparatus as recited in claim 8 wherein:
11. In combination with an apparatus as recited in claim 10, an apparatus for operating the musical instrument in a recreation of the original musical performance comprising:
12. An apparatus as recited in claim 8 wherein:
13. In combination with an apparatus recited as in claim 12, an apparatus for operating the musical instrument in a recreation of the original musical performance comprising:
14. An apparatus as recited in claim 8 for use with a keyboard instrument whose controls include a plurality of manually operated keys, wherein said sensing means further comprises a pair of electrical contacts coupled to each key and actuated upon depression thereof, a voltage source, and means connecting said voltage source to each of said contact pairs.
15. In combination with the apparatus recited in claim 14, an apparatus for recreating the original musical performance of the instrument comprising:
16. An apparatus as recited in claim 15, further comprising:
17. An apparatus as recited in claim 11 which is adapted to transpose the key signature of the original musical performance upon recreation thereof further comprising:
18. An apparatus such as recited in claim 11 which is adapted to modify the original musical performance upon recreation thereof by simultaneously operating predetermined combinations of the instrument controls, further comprising:
Description:
BACKGROUND OF THE INVENTION
This invention relates to musical instruments and, more particularly, to a method and to an apparatus for recreating a musical performance.
Practically everyone is familiar with player mechanisms for musical instruments. Perhaps the most common of these are those which have been adapted for pianos and organs. Such devices have been known for some time and generally operate from a prerecorded paper roll. A plurality of positions which are assigned to the various musical notes of the instrument extend across the roll. Holes are placed in the appropriate positions according to the musical composition to be reproduced. As the paper roll is advanced in a longitudinal direction by a transport mechanism, the hole positions are sensed by suitable means and output signals therefrom actuate the key mechanisms of the instrument so that the recorded musical performance is reproduced.
These player mechanisms are commonly made integral with the instrument and also include a speed control for the transport mechanism, a volume control, and other controls which make possible modification of the original musical performance.
While these devices made in the past many enjoyable moments for the listeners, in that a talented musical performance could be obtained by the simple purchase of a paper roll, they are relatively uncommon today. Around the turn of the century, player pianos, for example, were present in practically every household and commercial versions, better known as nickelodeons, pianolas, and the like, were available in every place of public amusement. With the advent of the inexpensive phonograph record and other means of artificial music reproduction, player mechanisms of this type fell into misuse and the manufacture thereof was severely curtailed.
Perhaps the best reason for such misuse lies in defects of the mechanisms. For example, these mechanisms are quite bulky, resulting either in a very large case for the piano or organ, if they are made an integral part thereof, or in a large and complicated contraption that must be utilized in conjunction with an existing instrument. Moreover, the paper rolls that must be used are in themselves bulky and require considerable space requirements, especially if a large library of musical compositions is to be maintained. Because of their paper composition, these rolls are constantly subject to breaking and tearing, and often distort the original musical composition upon reproduction. Moreover, the mechanical parts within the mechanism wear so that further distortion and unreliable performance results.
Another disadvantage of these prior mechanisms is their inflexibility with respect to the musical performances that can be rendered thereby. In a common situation, the paper roll is prerecorded at a central studio and then sold to the consumer for reproduction on his own instrument. Thus, the mechanisms that are used in the home or otherwise have only the capability of a limited type of playback that is restricted to the exact musical performance rendered at the originating studio. With such devices, there generally could be no accompaniment by the local musician, nor any improvisation or other changes of the original musical performance. Very seldom have instruments been provided with both a recording and a playback mechanism.
The devices proposed and manufactured during recent years have been mere reproductions of those which were designed more than a half century ago and embody few of the technical advances that have been made in the intervening period. Some improvements have been made, primarily in the characteristics of the recording medium. For example, one device comprises a translucent roll which has a plurality of opaque "notes" thereon which are relatively spaced across the roll so as to correctly play back a prerecorded composition when the roll is drawn past a plurality of optical sensors at a predetermined rate. The advantage of this system over those using paper rolls lies primarily in the ability to modify the translucent medium therein by changing the relative position of the opaque markings. However, this system is still primarily mechanical with all the inherent disadvantages thereof, such as limited flexibility upon playback, distortion due to wear, bulk, and the like.
Most important, this and prior devices are generally not adaptable or have not been adapted to the new types of musical instruments that have been recently developed, such as the electronic organ, the electronic piano, and others.
It is therefore an object of this invention to provide an improved method and apparatus for recording and playing back the activity of musical instruments.
It is a further object of this invention to provide an apparatus and a method which allow a musician or other to flexibly control the recreation of an original musical performance.
It is a further object of this invention to provide a method and an apparatus for the recreation of musical performances which are adaptable to practically any musical instrument which provides a plurality of signals therefrom corresponding to the occurrences of musical notes and other events during the performance and which in turn can be automatically controlled by a similar plurality of signals to recreate the performance.
It is another object of this invention to provide an apparatus for recording and playback of a musical performance on a musical instrument which is relatively inexpensive and reliable and which can be implemented by readily available components.
SUMMARY OF THE INVENTION
These objects and others are achieved, briefly, by time multiplexing the relative time occurrences of a plurality of signals obtained from a musical performance into a composite signal wherein each performance signal corresponds to a distinct musical event thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of this invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention both as to organization and as to mode of operation may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 shows in block diagram form the manner in which the various elements of the system are interconnected with one another and with the musical instrument that is to be recorded and played back;
FIGS. 2A and 2B show the electrical signal flow in the system and illustrate the principles of operation thereof in the record and playback modes, respectively;
FIG. 3 is a timing diagram showing the important waveforms of the electrical signals and the manner in which the keyboard sampling sequence is arranged;
FIG. 4 contains a pictorial and block diagram describing an embodiment of the system for an organ;
FIG. 5 is a timing diagram showing the waveform and assignment of notes to the counting sequence in the organ embodiment;
FIGS. 6, 7A, 7B, 7C, 8 and 9 are schematic diagrams of embodiments of the transistor switching matrix, the counter and gating circuits, the waveform generating circuits, and the playback threshold detectors of FIG. 5;
FIG. 10 illustrates another embodiment which allows remote control of a musical instrument using a single pair of wires;
FIG. 11 illustrates a variation to the preferred embodiment which allows octave or other interval coupling during playback of a keyboard instrument; and
FIG. 12 illustrates a piano embodiment, along with a variation for adding volume control thereto.
DESCRIPTION OF A PREFERRED EMBODIMENT
General Description
FIG. 1 shows, in block diagram form, the manner in which the various elements of this system are interconnected with one another and with the instrument that is to be recorded and played back.
Although the invention will be hereinafter described with particular reference to a keyboard instrument, it should be noted the apparatus and techniques thereof may be used with any musical instrument and any musical performance which is capable of providing a distinct signal upon the occurrence of each musical note emitted thereby or upon the occurrence of other events, such as volume modification, in the performance. In addition, the instrument should be capable of being played in response to similar, distinct signals which likewise correspond to the desired occurrences of musical notes and other events.
Upon recording, the method of one embodiment of this invention senses the time occurrences of keyboard depressions and other instrument events and produces therefrom an electrical output or composite signal which is suitable for recording by any recording means having a limited frequency response. Upon playback, the recorded electrical signal is used to actuate the keyboard and other controls to recreate the exact musical performance rendered by the musician upon the instrument.
In keyboard instruments such as the modern church or theater pipe organ, or the electronic organ, it is convenient to monitor key depressions because a plurality of electrical contacts are already installed under each key for use with the instrument playing apparatus. In this manner, a signal may be obtained from each key that is depressed by using existing contacts.
The common keyboard instrument has a plurality of keys, each key corresponding to a different musical pitch produced by the instrument. In the case of the piano, 88 such keys are provided. In other keyboard instruments, such as the organ, a fewer or a greater number of keys may be provided. It at once becomes evident that a typical recording means, such as an audio tape recorder, does not have a sufficient number of recording tracks to allow the signal from each key on the keyboard to occupy a separate track. For example, there are usually two to four tracks available on commercially available tape recorders.
The technique of this invention is based on the fact that a listener cannot detect a slight variation in the time at which a key is depressed and a musical note is thereby produced in a musical performance, if the variation is kept within a predetermined range dictated by the pitch of the musical note and its relation to other sequences of notes. Therefore, if the keyboard is scanned at a rate which allows sampling of the position of each key at intervals within this range, an accurate representation of time occurrences of key depressions can be produced.
In one embodiment of this invention, the up or down status of each key is determined by providing a repetitive, digital pulse train which includes in each cycle thereof a pulse location for each key, as well as additional pulse locations for other events associated with the musical instrument and for synchronizing pulses. The repetition rate of the pulse train determines the rate of sampling of the status of each key. During sampling, the key depressions are time multiplexed and the pulse train is modulated in a suitable manner. The modulated pulse train thus comprises a composite or electrical output signal and may be recorded by any means having a frequency response equal to the repetition rate of the pulse train, plus desired side bands.
For playback, this composite or electrical signal may be taken from the recording means and demultiplexed to provide a separate signal for each key depressed and event controlled in the exact time sequence in which the key depressions and events occurred. These signals are in turn used to operate the original instrument or other instruments in a manner identical to that recorded.
This method and an apparatus embodying the same can perhaps best be understood by reference to the details of the system in FIG. 1. Specifically, there are two basic functions which these elements perform when operating together as a system, i.e., recording and playback.
The recording function consists of generating a specially modulated electrical signal, termed the "record signal" 20 which is derived by electronically processing a plurality of signals that originate from the keyboard type of musical instrument 22. The record signal 20 is bandwidth limited such that it can be recorded on an audio recorder 24.
In the playback function, the system accepts the same specially modulated signal, now termed the "playback signal" 26 and, by means of electronic processing, produces a plurality of voltages which are connected to the musical instrument 22 and which cause the instrument to play in the same manner as originally performed by the musician.
The musical instrument 22 is shown in FIG. 1 as consisting of a keys/controls portion 28 and the playing mechanism 30. The keys/controls 28 contain the plurality of keyboard keys and those other controls (e.g., pedals, stop tabs, etc.) which are normally manipulated by the musician in performing a musical selection. Each key or control is equipped with an electrical contact. The contacts, which are disposed under the keys or controls, may already exist, as with a pipe or electronic organ, or may be specially installed for use with this system. During the recording process activation of each key by the musician, while playing the instrument in a normal manner, results in a voltage being supplied to the system via an appropriate electrical conductor in the multiconductor cable 32.
The instrument playing mechanism 30 consists of a plurality of electrically activated electromechanical, electronic, or electropneumatic mechanisms (depending upon the construction of the instrument in question). During playback, the mechanisms are provided with proper voltages from the system via cable 34 which cause the appropriate instrument actions to occur, identically to the manner in which they occurred while the musician originally performed the selection. The electrically activated mechanisms 30 may already exist as with a pipe organ, electronic organ, or certain brands of player pianos; or may be specially installed for use with this system.
The elements of the system which can be used to implement the record function include a transistor switching matrix 36, counter and gating circuits 38, and waveform generating circuits 40. To implement the playback function, the transistor switching matrix 36 and counter and gating circuits 38 are again utilized in addition to playback threshold detectors 42 and playback driver circuits 44. The elements are interconnected by the cables 32, 34, 46, 48 and switches 50, 52, and 54. Each of these elements is discussed in the subsequent paragraphs.
The transistor switching matrix 36, operating under the control of gating pulses 56 from the counter and gating circuits 38 performs the following functions:
1. During recording, it accepts, from the musical instrument, the plurality of electrical signals (via cable 32 and switch 52) which correspond to those keys being depressed at any given time period. One signal line input is furnished for each key or control. By sequentially sampling these signal lines, a single time-multiplexed signal output termed "multiplexed record key-on signal" 58 is developed. This signal is used subsequently in the system to develop the modulated recording waveform.
2. During playback, the matrix performs the inverse of the recording function. It accepts a signal containing the same sequentially sampled key data, now termed the "multiplexed playback key-on signal" 60 and by demultiplexing produces a plurality of signals which correspond to those particular keys or controls that are to be activated. These signals are routed to the playback driver circuits 44 via switch 52 and cable 48.
The functions of the counter and gating circuits 38 are to control the transistor switching matrix 36 both during recording and playback, and to furnish a first synchronization or record sync pulse 62 during recording to establish the start of a counting sequence.
A binary counter 64 develops the counting sequence which provides at least one count for each instrument key or control that is to be recorded. Decode gates 66 also within circuits 38 use the binary counter outputs 68 to develop the control gating pulses 56 which are used by the transistor switching matrix 36. A NAND gate 70 uses similar binary counter outputs 72 to develop one record sync pulse 62 during each sampling sequence. This pulse 62 is used subsequently in developing the modulated recording waveform.
During the recording process, the binary counter 64 is operated by counting "record clock" pulses 74 furnished by the waveform generating circuits 40. During playback, the binary counter 64 is operated by counting pulses termed "playback clock" 76 furnished by the playback threshold detector circuits 42.
A second synchronization pulse, playback sync pulse 78, which properly resets the binary counter 64 during playback, is also furnished by the playback threshold detector circuits 42.
The functions of the waveform generating circuits 40 are to develop the record clock pulse 74 used by the binary counter 64 during recording, and to produce the modulated recording waveform termed the "record signal" 20. The timing origin of both the record clock pulse 74 and the record signal 20 is the audio oscillator 80. A squaring circuit 82 is necessary to convert sine wave output 86 of the oscillator 80 into the record clock pulses 74. A key-on modulator circuit 84 utilizes the multiplexed record key-on signal 58, the record sync pulse 62, and the sine wave output 86 of the audio oscillator 80 to develop the record signal 20.
The function of the playback threshold detectors 42 (which consist of three threshold detectors 88, 90 and 92, and a key-on driver 94) is to extract from the playback signal 26 the essential signals needed to operate the system during playback. These include playback clock 76 pulses, the playback sync pulse 78, and the multiplexed playback key-on signal 60. As previously described, the counter and gating circuits 38 and the transistor switching matrix 36 utilize these signals to develop the plurality of signals needed to operate the playback driver circuits 44.
The function of the playback driver circuits 44 is to provide a steady and proper voltage level to the instrument playing mechanism 30 during playback. A separate driver circuit is provided to correspond to each note or other mechanism within the musical instrument which is to be played or sounded. Cable 34 and switch 50 conducts the current to the instrument playing mechanism 30.
PRINCIPLES OF OPERATION
FIGS. 2A and 2B illustrate the signal flow for the recording and playback modes, respectively, and are used in conjunction with FIG. 3, which illustrates the essential waveforms, to describe the principles of operation of the system.
With regard to the recording process, the signals which are to be recorded originate at the keyboard/controls portion 28 of the musical instrument which is shown in FIG. 2A as a plurality of switches 96. Depression of a key or control by the musician causes a supply voltage to be coupled to an input of the transistor switching matrix 36. One input is furnished for each key or control. (Only one input is shown for illustrative purposes.) The gating pulses 56 from the counter and gating circuits 38 are routed to the bases of the switching transistors 98. Isolation diodes 100 are also included to prevent current from being fed back to the musical instrument. The transistor switching matrix 36 is arranged such that during each count of the binary counter 64, base drive current from the gating pulses 56 will allow one and only one input to the matrix to make a complete conductive path to the matrix output at a time. During each individual clock count, a different input is allowed to conduct to the output. The counters 64, decode gates 66, and transistor switching matrix 36 therefore constitute a time-sharing multiplexer which scans the entire set of signal lines connected to the matrix inputs; and sequentially registers the ON or OFF status of each signal line (switch contact 96) onto a common signal output termed the "multiplexed record key-on signal" 58.
The arrangement or organization of the multiplexing or sampling sequence is illustrated in FIG. 3. FIG. 3 also shows the time relationship between signals. The sequence is comprised of N counts per cycle, where N is the number of keys or controls which are to be recorded plus one count for synchronization purposes.
Referring to both FIG. 2A and 3, it is seen that the key-on modulator circuit 84 accepts the multiplexed record key-on signal 58, the record sync signal 62, the sine wave output 86 from the audio oscillator 80 and produces an amplitude modulated output record signal 20. The record signal 20 contains one full sinusoidal cycle for each key or control signal line plus one cycle for synchronization. Each key or control is therefore assigned to one particular count in the sequence, and therefore always has the same relationship to the synchronization count. Whether a particular key or control is on or off, i.e., played or not played, is indicated by the amplitude of the particular count assigned to that key or control. There are three possible amplitudes or levels:
1. the synchronization level, which is the highest level and used only for the synchronization count;
2. the key-on level, which is the intermediate level, used for each key or control that is being played at that particular instant of sampling; and
3. the clocking level, or lowest level, which is used for those keys not being played.
The frequency of the record signal 20 is determined by the number of counts in the frame or cycle (i.e., number of keys or controls), multiplied by the desired frame sampling rate. A frame sampling rate of 50 to 100 samples per second is usually adequate to represent the key position without any detectable audio distortion effect to the human ear when the selection is played back. For example, a complete 88 key piano keyboard can thus be handled with less than a 9,000 Hz. modulated tone when scanning or sampling the keyboard at 100 frames per second. Because a sinusoidal-type waveform is used, rather than a square wave (which contains many high harmonic components), the 9,000 Hz. tone and its associated modulation side bands can readily be handled by an audio recorder 24 having a 15,000 Hz. frequency response.
With a standard two-track home audio tape recorder, for example, it is apparent that many keys or controls can be recorded which may originate from a very large instrument, such as a theatre pipe organ.
FIG. 2B illustrates the playback mode. The playback signal 26 is identical to the record signal 20 except for slight noise and distortion introduced by the audio recorder 24. The playback signal 26 is applied to the threshold detectors 42. Three threshold detectors are provided, each of which corresponds to one of the three amplitude levels of the playback signal 26. Each threshold detector is a device which will issue a pulse output whenever a preset, predetermined input amplitude is exceeded. The threshold detector 90 for detecting synchronization is set at a high enough level that it registers an output when the synchronization level occurs on the playback signal, but is insensitive to the key-on level and clock level. The resulting playback sync pulse 78 is used to reset the counter to zero. The threshold detector 92 for key-on level detects both the synchronization level and the key-on level; however, no key or playback mechanism is assigned to count zero, so that no unwanted sounds are caused thereby. The resulting output, after buffering by the key-on driver 94, is the multiplexed playback key-on signal 60 which drives the transistor tree matrix 36 during playback. The clock threshold detector 88 provides an output for all three levels, thereby driving a playback clock signal 76 which can be used to operate the counter and gating circuits 38.
The three signals which are extracted from the playback signal 26 by the threshold detectors 42 (i.e., playback sync 78, playback clock 76 and multiplexed playback key-on 60) all bear the exact time relationship to one another that their counterpart signals (i.e., record sync 62, record clock 74, and multiplexed record key-on 58) bore during recording. Therefore, the same transistor switching matrix 36 functioning under the control of the same counter and gating circuits 38 can be used to produce the control signals which will ultimately cause the playing mechanisms 30 to function, each at the precisely correct time with respect to one another.
In the playback mode, each playback driver circuit 44 is routed to one input of transistor switching matrix 36. There is a plurality of playback driver circuits, i.e., one circuit for each electrically activated playing mechanism 30. Only one playback driver circuit 44 is shown in FIG. 2B. The capacitor 102 is charged to the supply voltage and transistor 104 is off during the normal quiescent condition when no action is desired from that particular mechanism. During playback, when a particular key is supposed to play, the key-on threshold detector 92 will detect a key-on level for that key at the proper count to which the key is assigned. A key-on logic level will therefore appear on the multiplexed playback key-on signal 60. The key-on driver circuit 94 will allow the matrix to rapidly conduct current and thus discharge capacitor 102 to ground, during only that particular count. Sufficient charge will be drained from capacitor 102 that the transistor 104 will change to a conducting state. The RC combination of 102 and 106 is designed such that transistor 104 will stay in conduction for slightly more than the time for one complete sampling frame, i.e., approximately 1/100th second if a 100 sample per second frame is used. This scheme allows the transistor 104 to remain conducting for as many consecutive frames as the particular key or control was held depressed by the musician during the recording process. When the key is supposed to go off, the threshold detector 92 will no longer detect a key-on level at the proper count. The transistor switching matrix 36 will therefore not be enabled to conduct current during that particular count. The capacitor 102 will charge through the transistor 104 emitter-base junction and resistors 106 and 108 causing transistor 104 to go OFF and remain OFF until the note is again called upon to play.
ORGAN EMBODIMENT
FIGS. 4 through 9 describe a specific embodiment which has been fabricated to test and demonstrate the performance capability of the system. This embodiment relates to a pipe organ, and provides the capability to record one complete 61 note organ manual plus two sets of expression shutters, or a total of 63 existing and controls. key or existing electropneumatic
Referring to FIG. 4, the existing organ console 110 contains the plurality of electrical switch contacts 96, one for each key and control. Through various existing switching circuits within the console, the signal associated with each key depression or shutter pedal movement ultimately appears at terminal board 112, at which point the wires to the existing windchest attachment The windchest 114 contains a plurality of electropneumatic relays 116 which perform the function of allowing air to enter the proper pipe when played. The existing expression shutters 1118 also contain electropneumatic relays 116 which control movement of air into sets of bellows which open or shut the shutters to affect volume control. Each of the electropneumatic relays 116, as illustrated in FIG. 4, is a solenoid. Fifteen volts DC is used by the existing system for an activating source.
The system is connected to the organ at terminal board 120. Transient suppression diodes 122 for each electrical contact prevent high transient voltages associated with interrupting electrical current to the highly inductive electropneumatic coils from damaging the system transistors. The multiconductor cable 32, 34 conducts the electrical key and control depression signals to the system during recording and the playback drive signals to the organ during playback.
The elements of this embodiment, though specifically sized to this system, are functionally identical to those previously described in the preferred embodiment. They consist of the transistor switching matrix 36, the counter and gating circuits 38, waveform generating circuits 40, playback threshold detectors 42, playback driver circuits 44, and associated interconnecting cables and switches. The recorder 24 is an existing home use audio tape recorder.
FIG. 5 illustrates the arrangement of assigning notes to the various counts. In the 64 count frame, count zero was used for synchronization, counts 2 through 62 for low C to high C, inclusive, and counts 1 and 62 for expression shutters. Four expression shutters are coupled to each of the two counts, thus eight total shutters can be controlled. A sampling frame of 621/2 frames per second is used, resulting in a 4,000 Hz. modulation waveform frequency. Because of the internal coupling arrangements within the existing organ console, it is possible to play from both manuals as well as the pedals. A total of four ranks of pipes can be selected by the stop tabs, thus allowing control by the system of a total of 244 pipes.
The elements of the system illustrated in FIG. 5 have been constructed as shown and described with reference to FIGS. 6-9. Of course, these elements are merely exemplary and could be embodied in many other forms, as indicated hereinafter.
The transistor switching matrix 36 is shown in FIG. 6. A total of 64 input transistors 98 accept the signals from the 63 key or shutter control contacts. The numerical value of each channel input corresponds to the count number in the sampling frame. The 64 input transistors are arranged in 16 groups of four each. Each group is further tiered into groups of four until, after three tiers, a single output is obtained. The gating pulses 56 from the counter circuits are applied directly to the bases of the transistors. The individual gating pulse designations shown in FIG. 6 are consistent with that shown in FIGS. 7A, 7B, and 7C, which shows the counter and gating circuits 38.
Referring to FIGS. 7A-7C, the binary counter 64 consists of six flip-flops 126 arranged to form a standard binary ripple counter capable of a counting sequence containing 64 counts, designated 0 through 63 , inclusive. The counter trigger pulses are 74 and 76, the record of playback clock pulses, respectively. The flip-flop outputs, designated A through F, are each routed to an inverting amplifier 128 to provide the necessary logical prime signals designated A through F. The AND gates 130 are arranged to provide a total of 12 gating pulse outputs. These are buffered by transistors 132 and then routed to the bases of the transistors in the transistor switching matrix 36 of FIG. 6. A positive voltage swing represents a logical true level on the gating pulse outputs. NAND gate 134, which generates the record sync pulse 62, is furnished the primed outputs from each counter stage, thus providing a negative-going sync pulse 62 only during count zero. The flip-flops 126, inverters 128, AND gate 130, and NAND gate 134 are all implemented with microminiature integrated circuits.
FIG. 8 illustrates the waveform generating circuits 40. The audio oscillator 80 consists of transistor 136 and the associated inductor 138, capacitor 140 and other components which connect to it. Transistor 142 forms an amplifier circuit to provide adequate signal level to operate the remaining circuits. The squaring circuit 82 uses three active circuits formed by transistors 144, 146, and 148 which provide the proper square wave rise times, and voltage levels suitable to drive the binary counter 64 of FIG. 7A. The key-on modulator circuit 84 functions to change the amplitude of the sine wave 86 on a per cycle basis, depending upon whether it is to represent sync level, key-on level, or clock level. The heart of the modulator is transistors 150, 152, 154 and 156. The remaining transistors 158 and 160 are used for buffering and inverting, respectively. At the emitter of 158 the highest level audio signal, i.e., sync level, is always present. However, transistors 150 and 152 are normally conducting when no sync or key-on pulses are present, thus a voltage divider is formed with resistors 162, 164, and 166. The audio signal therefore becomes attenuated to its lowest level, i.e., the clock level at the junction where 162, 164 and 166 are connected together.
To obtain the synchronization level, transistors 150 and 152 must be shut off. This occurs when the negative synchronization pulse 62 is applied during the count "zero." To obtain the key-on level, transistor 152 must be shut off. This occurs when a positive level is present on the multiplexed record key-on signal 58. Resistor 168 and capacitor 170 form an RC filter to eliminate spikes form the record signal 20 which may degrade the recording.
FIG. 9 shows the threshold detectors 42. Differential comparators 172, 174 and 176, implemented with integrated circuits, form the heart of the circuit. These devices provide an output logic true level when the input voltage at point A exceeds that on point B. The point B levels, therefore establish the threshold levels for detecting clock, sync, and key-on levels on the playback signal 26. The exact threshold levels are individually adjustable by potentiometers 178, 180 and 182. The playback signal 26 is buffered by transistor 184 and is applied to all three differential comparators. Transistors 186 and 188 form inverting and level shifting circuits for the playback clock 76 and playback sync 78 signals to produce proper signal levels for driving the counter circuits. Transistors 190 and 192 form the key-on driver circuit 94 which forms the multiplexed playback key-on signal 60. This signal connects to the transistor switching matrix 36 (FIG. 6).
OTHER APPLICATIONS
Remote Keyboard
Although the elements of this invention have been described as operating in a record and playback fashion, the identical elements can also be used in another potentially useful application, i.e., operation of remote keyboard(s). FIG. 10 illustrates the remote keyboard function. The keyboard inputs are processed identically to the manner previously described, except that the output of the key-on modulator 84 formerly designated the record signal 20 is now routed to a long line, i.e., a single pair of wires, rather than to the tape recorder. At the receiving end the threshold detectors 42' accept the signal 26', formerly designated the signal 26. The instrument playing mechanism 30' is thereby activated as previously described.
The remote keyboard application thus provides the capability to control a large plurality of instrument functions on a single pair of wires over any desired distance. It also allows any desired number of keyboards to share a single instrument playing mechanism. If the playing mechanism has an electronic audio output signal, such as an electronic organ, it can be routed on a pair of wires to the area where the keyboard performance is being initiated, and heard on a loudspeaker 194.
This scheme can also allow one performer to simultaneously play any desired number of instruments by providing the playback-type circuitry or each instrument.
KEYBOARD TRANSPOSITION AND COUPLING (UNIFICATION)
FIG. 11 shows a variation which allows the musician to (1) transpose the key signature of the selection being played back and (2) add additional tones at a desired interval (e.g., octave coupling, fifth coupling, etc.--also termed "unification" in the organ field).
Referring to FIG. 11, two sets of counter and gating circuits 38a and 38b are provided. These perform the same function as previously described, i.e., each set of counter and gating circuits 38a and 38b issues gating pulses 56 to the transistor switching matrix 36. By controlling the time position of the synchronization pulses to these counter and gating circuits 38a and 38b relative to the playback sync pulse 78, transposition and coupling will result. This is true provided that a sequential arrangement of assigning notes to counts, as shown in FIG. 5, is adhered to.
Transposition is implemented as follows (FIG. 11). The binary counter 64, identical to the counter in the counter and gating circuits 38 of FIG. 1, operates in conjunction with the transposition interval gates 196 to produce sync pulse 198. Sync pulse 198 causes the basic key signature to be transposed by one half-step for each count difference between sync pulse 198 and the occurrence of playback sync 78. This difference is established by the logical combination of binary counter outputs fed to the transposition interval gates 196. The interval can be made selectable by switch 200 by providing a gate 202 for each desired interval. When no transposition is desired, sync pulse 198 is made to occur simultaneously with the playback sync pulse 78.
The coupling (unification) function operates as follows. The counter and gating circuits 38b, synchronized by sync pulse 204, provides a second set of gating pulses 56 to the transistor switching matrix 36. The end result of the second-gating pulses is that an additional playback mechanism will be activated, i.e., an additional tone will be generated for each of the tones originally recorded. The second tone will differ in pitch from the original tone by one half-step for each count difference between sync pulses 198 and sync pulse 204. This difference is established by the coupling interval gates 206 and can also be made selectable by switch 208 by providing a gate 210 for each desired interval.
PIANO KEYBOARD EMBODIMENT
The basic embodiment described in FIGS. 1 through 3 is directly applicable to a piano insofar as recording and playing back the occurrences of key depressions is concerned. The expression or volume control aspect of the piano can also be implemented within the sequential sampling frame by: (1) allocating specific counts or channels to the task of volume control; (2) providing adequate sensing means to register the level information onto the recording waveform; and (3) providing playback activating means.
Another scheme, involving use of the second track of a two-track audio recorder is also feasible. In FIG. 12A, which depicts the recording mode, it is seen that the elements of the system required to record the occurrences of keys being depressed are identical to those previously described in FIGS. 1 through 3. The switch 96 consists of a standard organ-type key contact 212 placed under each key 214 and a standard contact block 216 mounted on the main console.
The additional elements, associated with recording of volume, include use of a volume modulator circuit 218, a separate track (designated channel 2) on the recorder 24, and a volume sensing device 222. The volume sensing device 222 produces a voltage proportional to the volume or loudness of the keys being played at any time. The configuration of the volume sensing device 222, though not specified herein, could, for example, consist of a manually activated potentiometer device, or it may consist of a more elaborate device which will sense velocity on the individual keys or hammers. Devices incorporating added, precisely spaced contacts on the contact blocks could also provide a means for sensing velocity of individual keys.
The key volume signal 224 is coupled to the volume modulator circuit, which creates an amplitude modulated sinusoidal waveform 220. The waveform, as shown in FIG. 12C need not be a multiplexed signal, as is the key-on record signal 20, because during the playback mode, only one playback driver is ever activated at a given instant.
FIG. 12B illustrates the playback function. The elements associated with defining the occurrences of key-on are identical to those previously described, except that the playback driver circuit 226 is modified. The volume driver circuit 228 detects the channel 2 volume signal 230 and provides a signal 232 to each of the playback drivers accordingly. Each playback driver circuit adjusts the voltage applied to each key activating solenoid 234 in accordance with the magnitude of the output signal 232 from the volume driver circuit 228.
ALTERNATIVES
Although the method and apparatus of this invention have been described with respect to a particular embodiment thereof, it should be clear to one skilled in the art that they could be implemented in many alternative ways without falling outside the scope or spirit of this invention.
For example, the logical functions involved, including counting and the assigning of keys or controls to specific counts, may be altered to fit any particular cost or functional requirement. In the embodiment of FIGS. 7A, 7B and 7C, the binary ripple counters therein could be replaced by shift register counters. The transistor tree matrix 36 of FIG. 6 could be replaced by a gating means in which a single-gating pulse is assigned to each count.
Likewise, the record signal 20 is shown to include an amplitude modulated sine wave. If appropriate circuitry can be provided, the method of this invention could also be implemented by phase modulation, for example. The selection of a waveform and a modulating technique is dependent upon the complexity of circuitry required to generate and detect the record signal 20, and the ability of the audio recorder 24 to accommodate the frequency spectrum of the record signal without significant distortion.
As previously indicated, the frequency of the recording waveform can be varied as long as a sufficiently high frame sampling rate is achieved such that no noticeable distortion occurs during playback. In the remote keyboard application of FIG. 10, a substantially higher frequency than that available for recording can be used because of the improved frequency response characteristics of a pair of electrical conductors as opposed to conventional audio recorders. With such applications, a significantly larger number of keys and controls can be included in the system.
Again with reference to the particular embodiments of FIGS. 5-9, the circuitry therein has not been optimized to achieve minimum hardware cost and maximum performance. It is not intended that the invention be limited to such circuitry and in fact, it would be desirable to add elements thereto which would make this system easier to operate by anyone. Such elements as an automatic gain control circuit for the record and playback signals, record and playback level meters, and others might well be included.
It is clear, then, that the invention, although having been described in terms of a preferred embodiment, is not to be limited thereto, and is in fact to be bounded only by the limits of the appended claims.
This invention relates to musical instruments and, more particularly, to a method and to an apparatus for recreating a musical performance.
Practically everyone is familiar with player mechanisms for musical instruments. Perhaps the most common of these are those which have been adapted for pianos and organs. Such devices have been known for some time and generally operate from a prerecorded paper roll. A plurality of positions which are assigned to the various musical notes of the instrument extend across the roll. Holes are placed in the appropriate positions according to the musical composition to be reproduced. As the paper roll is advanced in a longitudinal direction by a transport mechanism, the hole positions are sensed by suitable means and output signals therefrom actuate the key mechanisms of the instrument so that the recorded musical performance is reproduced.
These player mechanisms are commonly made integral with the instrument and also include a speed control for the transport mechanism, a volume control, and other controls which make possible modification of the original musical performance.
While these devices made in the past many enjoyable moments for the listeners, in that a talented musical performance could be obtained by the simple purchase of a paper roll, they are relatively uncommon today. Around the turn of the century, player pianos, for example, were present in practically every household and commercial versions, better known as nickelodeons, pianolas, and the like, were available in every place of public amusement. With the advent of the inexpensive phonograph record and other means of artificial music reproduction, player mechanisms of this type fell into misuse and the manufacture thereof was severely curtailed.
Perhaps the best reason for such misuse lies in defects of the mechanisms. For example, these mechanisms are quite bulky, resulting either in a very large case for the piano or organ, if they are made an integral part thereof, or in a large and complicated contraption that must be utilized in conjunction with an existing instrument. Moreover, the paper rolls that must be used are in themselves bulky and require considerable space requirements, especially if a large library of musical compositions is to be maintained. Because of their paper composition, these rolls are constantly subject to breaking and tearing, and often distort the original musical composition upon reproduction. Moreover, the mechanical parts within the mechanism wear so that further distortion and unreliable performance results.
Another disadvantage of these prior mechanisms is their inflexibility with respect to the musical performances that can be rendered thereby. In a common situation, the paper roll is prerecorded at a central studio and then sold to the consumer for reproduction on his own instrument. Thus, the mechanisms that are used in the home or otherwise have only the capability of a limited type of playback that is restricted to the exact musical performance rendered at the originating studio. With such devices, there generally could be no accompaniment by the local musician, nor any improvisation or other changes of the original musical performance. Very seldom have instruments been provided with both a recording and a playback mechanism.
The devices proposed and manufactured during recent years have been mere reproductions of those which were designed more than a half century ago and embody few of the technical advances that have been made in the intervening period. Some improvements have been made, primarily in the characteristics of the recording medium. For example, one device comprises a translucent roll which has a plurality of opaque "notes" thereon which are relatively spaced across the roll so as to correctly play back a prerecorded composition when the roll is drawn past a plurality of optical sensors at a predetermined rate. The advantage of this system over those using paper rolls lies primarily in the ability to modify the translucent medium therein by changing the relative position of the opaque markings. However, this system is still primarily mechanical with all the inherent disadvantages thereof, such as limited flexibility upon playback, distortion due to wear, bulk, and the like.
Most important, this and prior devices are generally not adaptable or have not been adapted to the new types of musical instruments that have been recently developed, such as the electronic organ, the electronic piano, and others.
It is therefore an object of this invention to provide an improved method and apparatus for recording and playing back the activity of musical instruments.
It is a further object of this invention to provide an apparatus and a method which allow a musician or other to flexibly control the recreation of an original musical performance.
It is a further object of this invention to provide a method and an apparatus for the recreation of musical performances which are adaptable to practically any musical instrument which provides a plurality of signals therefrom corresponding to the occurrences of musical notes and other events during the performance and which in turn can be automatically controlled by a similar plurality of signals to recreate the performance.
It is another object of this invention to provide an apparatus for recording and playback of a musical performance on a musical instrument which is relatively inexpensive and reliable and which can be implemented by readily available components.
SUMMARY OF THE INVENTION
These objects and others are achieved, briefly, by time multiplexing the relative time occurrences of a plurality of signals obtained from a musical performance into a composite signal wherein each performance signal corresponds to a distinct musical event thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter of this invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention both as to organization and as to mode of operation may best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:
FIG. 1 shows in block diagram form the manner in which the various elements of the system are interconnected with one another and with the musical instrument that is to be recorded and played back;
FIGS. 2A and 2B show the electrical signal flow in the system and illustrate the principles of operation thereof in the record and playback modes, respectively;
FIG. 3 is a timing diagram showing the important waveforms of the electrical signals and the manner in which the keyboard sampling sequence is arranged;
FIG. 4 contains a pictorial and block diagram describing an embodiment of the system for an organ;
FIG. 5 is a timing diagram showing the waveform and assignment of notes to the counting sequence in the organ embodiment;
FIGS. 6, 7A, 7B, 7C, 8 and 9 are schematic diagrams of embodiments of the transistor switching matrix, the counter and gating circuits, the waveform generating circuits, and the playback threshold detectors of FIG. 5;
FIG. 10 illustrates another embodiment which allows remote control of a musical instrument using a single pair of wires;
FIG. 11 illustrates a variation to the preferred embodiment which allows octave or other interval coupling during playback of a keyboard instrument; and
FIG. 12 illustrates a piano embodiment, along with a variation for adding volume control thereto.
DESCRIPTION OF A PREFERRED EMBODIMENT
General Description
FIG. 1 shows, in block diagram form, the manner in which the various elements of this system are interconnected with one another and with the instrument that is to be recorded and played back.
Although the invention will be hereinafter described with particular reference to a keyboard instrument, it should be noted the apparatus and techniques thereof may be used with any musical instrument and any musical performance which is capable of providing a distinct signal upon the occurrence of each musical note emitted thereby or upon the occurrence of other events, such as volume modification, in the performance. In addition, the instrument should be capable of being played in response to similar, distinct signals which likewise correspond to the desired occurrences of musical notes and other events.
Upon recording, the method of one embodiment of this invention senses the time occurrences of keyboard depressions and other instrument events and produces therefrom an electrical output or composite signal which is suitable for recording by any recording means having a limited frequency response. Upon playback, the recorded electrical signal is used to actuate the keyboard and other controls to recreate the exact musical performance rendered by the musician upon the instrument.
In keyboard instruments such as the modern church or theater pipe organ, or the electronic organ, it is convenient to monitor key depressions because a plurality of electrical contacts are already installed under each key for use with the instrument playing apparatus. In this manner, a signal may be obtained from each key that is depressed by using existing contacts.
The common keyboard instrument has a plurality of keys, each key corresponding to a different musical pitch produced by the instrument. In the case of the piano, 88 such keys are provided. In other keyboard instruments, such as the organ, a fewer or a greater number of keys may be provided. It at once becomes evident that a typical recording means, such as an audio tape recorder, does not have a sufficient number of recording tracks to allow the signal from each key on the keyboard to occupy a separate track. For example, there are usually two to four tracks available on commercially available tape recorders.
The technique of this invention is based on the fact that a listener cannot detect a slight variation in the time at which a key is depressed and a musical note is thereby produced in a musical performance, if the variation is kept within a predetermined range dictated by the pitch of the musical note and its relation to other sequences of notes. Therefore, if the keyboard is scanned at a rate which allows sampling of the position of each key at intervals within this range, an accurate representation of time occurrences of key depressions can be produced.
In one embodiment of this invention, the up or down status of each key is determined by providing a repetitive, digital pulse train which includes in each cycle thereof a pulse location for each key, as well as additional pulse locations for other events associated with the musical instrument and for synchronizing pulses. The repetition rate of the pulse train determines the rate of sampling of the status of each key. During sampling, the key depressions are time multiplexed and the pulse train is modulated in a suitable manner. The modulated pulse train thus comprises a composite or electrical output signal and may be recorded by any means having a frequency response equal to the repetition rate of the pulse train, plus desired side bands.
For playback, this composite or electrical signal may be taken from the recording means and demultiplexed to provide a separate signal for each key depressed and event controlled in the exact time sequence in which the key depressions and events occurred. These signals are in turn used to operate the original instrument or other instruments in a manner identical to that recorded.
This method and an apparatus embodying the same can perhaps best be understood by reference to the details of the system in FIG. 1. Specifically, there are two basic functions which these elements perform when operating together as a system, i.e., recording and playback.
The recording function consists of generating a specially modulated electrical signal, termed the "record signal" 20 which is derived by electronically processing a plurality of signals that originate from the keyboard type of musical instrument 22. The record signal 20 is bandwidth limited such that it can be recorded on an audio recorder 24.
In the playback function, the system accepts the same specially modulated signal, now termed the "playback signal" 26 and, by means of electronic processing, produces a plurality of voltages which are connected to the musical instrument 22 and which cause the instrument to play in the same manner as originally performed by the musician.
The musical instrument 22 is shown in FIG. 1 as consisting of a keys/controls portion 28 and the playing mechanism 30. The keys/controls 28 contain the plurality of keyboard keys and those other controls (e.g., pedals, stop tabs, etc.) which are normally manipulated by the musician in performing a musical selection. Each key or control is equipped with an electrical contact. The contacts, which are disposed under the keys or controls, may already exist, as with a pipe or electronic organ, or may be specially installed for use with this system. During the recording process activation of each key by the musician, while playing the instrument in a normal manner, results in a voltage being supplied to the system via an appropriate electrical conductor in the multiconductor cable 32.
The instrument playing mechanism 30 consists of a plurality of electrically activated electromechanical, electronic, or electropneumatic mechanisms (depending upon the construction of the instrument in question). During playback, the mechanisms are provided with proper voltages from the system via cable 34 which cause the appropriate instrument actions to occur, identically to the manner in which they occurred while the musician originally performed the selection. The electrically activated mechanisms 30 may already exist as with a pipe organ, electronic organ, or certain brands of player pianos; or may be specially installed for use with this system.
The elements of the system which can be used to implement the record function include a transistor switching matrix 36, counter and gating circuits 38, and waveform generating circuits 40. To implement the playback function, the transistor switching matrix 36 and counter and gating circuits 38 are again utilized in addition to playback threshold detectors 42 and playback driver circuits 44. The elements are interconnected by the cables 32, 34, 46, 48 and switches 50, 52, and 54. Each of these elements is discussed in the subsequent paragraphs.
The transistor switching matrix 36, operating under the control of gating pulses 56 from the counter and gating circuits 38 performs the following functions:
1. During recording, it accepts, from the musical instrument, the plurality of electrical signals (via cable 32 and switch 52) which correspond to those keys being depressed at any given time period. One signal line input is furnished for each key or control. By sequentially sampling these signal lines, a single time-multiplexed signal output termed "multiplexed record key-on signal" 58 is developed. This signal is used subsequently in the system to develop the modulated recording waveform.
2. During playback, the matrix performs the inverse of the recording function. It accepts a signal containing the same sequentially sampled key data, now termed the "multiplexed playback key-on signal" 60 and by demultiplexing produces a plurality of signals which correspond to those particular keys or controls that are to be activated. These signals are routed to the playback driver circuits 44 via switch 52 and cable 48.
The functions of the counter and gating circuits 38 are to control the transistor switching matrix 36 both during recording and playback, and to furnish a first synchronization or record sync pulse 62 during recording to establish the start of a counting sequence.
A binary counter 64 develops the counting sequence which provides at least one count for each instrument key or control that is to be recorded. Decode gates 66 also within circuits 38 use the binary counter outputs 68 to develop the control gating pulses 56 which are used by the transistor switching matrix 36. A NAND gate 70 uses similar binary counter outputs 72 to develop one record sync pulse 62 during each sampling sequence. This pulse 62 is used subsequently in developing the modulated recording waveform.
During the recording process, the binary counter 64 is operated by counting "record clock" pulses 74 furnished by the waveform generating circuits 40. During playback, the binary counter 64 is operated by counting pulses termed "playback clock" 76 furnished by the playback threshold detector circuits 42.
A second synchronization pulse, playback sync pulse 78, which properly resets the binary counter 64 during playback, is also furnished by the playback threshold detector circuits 42.
The functions of the waveform generating circuits 40 are to develop the record clock pulse 74 used by the binary counter 64 during recording, and to produce the modulated recording waveform termed the "record signal" 20. The timing origin of both the record clock pulse 74 and the record signal 20 is the audio oscillator 80. A squaring circuit 82 is necessary to convert sine wave output 86 of the oscillator 80 into the record clock pulses 74. A key-on modulator circuit 84 utilizes the multiplexed record key-on signal 58, the record sync pulse 62, and the sine wave output 86 of the audio oscillator 80 to develop the record signal 20.
The function of the playback threshold detectors 42 (which consist of three threshold detectors 88, 90 and 92, and a key-on driver 94) is to extract from the playback signal 26 the essential signals needed to operate the system during playback. These include playback clock 76 pulses, the playback sync pulse 78, and the multiplexed playback key-on signal 60. As previously described, the counter and gating circuits 38 and the transistor switching matrix 36 utilize these signals to develop the plurality of signals needed to operate the playback driver circuits 44.
The function of the playback driver circuits 44 is to provide a steady and proper voltage level to the instrument playing mechanism 30 during playback. A separate driver circuit is provided to correspond to each note or other mechanism within the musical instrument which is to be played or sounded. Cable 34 and switch 50 conducts the current to the instrument playing mechanism 30.
PRINCIPLES OF OPERATION
FIGS. 2A and 2B illustrate the signal flow for the recording and playback modes, respectively, and are used in conjunction with FIG. 3, which illustrates the essential waveforms, to describe the principles of operation of the system.
With regard to the recording process, the signals which are to be recorded originate at the keyboard/controls portion 28 of the musical instrument which is shown in FIG. 2A as a plurality of switches 96. Depression of a key or control by the musician causes a supply voltage to be coupled to an input of the transistor switching matrix 36. One input is furnished for each key or control. (Only one input is shown for illustrative purposes.) The gating pulses 56 from the counter and gating circuits 38 are routed to the bases of the switching transistors 98. Isolation diodes 100 are also included to prevent current from being fed back to the musical instrument. The transistor switching matrix 36 is arranged such that during each count of the binary counter 64, base drive current from the gating pulses 56 will allow one and only one input to the matrix to make a complete conductive path to the matrix output at a time. During each individual clock count, a different input is allowed to conduct to the output. The counters 64, decode gates 66, and transistor switching matrix 36 therefore constitute a time-sharing multiplexer which scans the entire set of signal lines connected to the matrix inputs; and sequentially registers the ON or OFF status of each signal line (switch contact 96) onto a common signal output termed the "multiplexed record key-on signal" 58.
The arrangement or organization of the multiplexing or sampling sequence is illustrated in FIG. 3. FIG. 3 also shows the time relationship between signals. The sequence is comprised of N counts per cycle, where N is the number of keys or controls which are to be recorded plus one count for synchronization purposes.
Referring to both FIG. 2A and 3, it is seen that the key-on modulator circuit 84 accepts the multiplexed record key-on signal 58, the record sync signal 62, the sine wave output 86 from the audio oscillator 80 and produces an amplitude modulated output record signal 20. The record signal 20 contains one full sinusoidal cycle for each key or control signal line plus one cycle for synchronization. Each key or control is therefore assigned to one particular count in the sequence, and therefore always has the same relationship to the synchronization count. Whether a particular key or control is on or off, i.e., played or not played, is indicated by the amplitude of the particular count assigned to that key or control. There are three possible amplitudes or levels:
1. the synchronization level, which is the highest level and used only for the synchronization count;
2. the key-on level, which is the intermediate level, used for each key or control that is being played at that particular instant of sampling; and
3. the clocking level, or lowest level, which is used for those keys not being played.
The frequency of the record signal 20 is determined by the number of counts in the frame or cycle (i.e., number of keys or controls), multiplied by the desired frame sampling rate. A frame sampling rate of 50 to 100 samples per second is usually adequate to represent the key position without any detectable audio distortion effect to the human ear when the selection is played back. For example, a complete 88 key piano keyboard can thus be handled with less than a 9,000 Hz. modulated tone when scanning or sampling the keyboard at 100 frames per second. Because a sinusoidal-type waveform is used, rather than a square wave (which contains many high harmonic components), the 9,000 Hz. tone and its associated modulation side bands can readily be handled by an audio recorder 24 having a 15,000 Hz. frequency response.
With a standard two-track home audio tape recorder, for example, it is apparent that many keys or controls can be recorded which may originate from a very large instrument, such as a theatre pipe organ.
FIG. 2B illustrates the playback mode. The playback signal 26 is identical to the record signal 20 except for slight noise and distortion introduced by the audio recorder 24. The playback signal 26 is applied to the threshold detectors 42. Three threshold detectors are provided, each of which corresponds to one of the three amplitude levels of the playback signal 26. Each threshold detector is a device which will issue a pulse output whenever a preset, predetermined input amplitude is exceeded. The threshold detector 90 for detecting synchronization is set at a high enough level that it registers an output when the synchronization level occurs on the playback signal, but is insensitive to the key-on level and clock level. The resulting playback sync pulse 78 is used to reset the counter to zero. The threshold detector 92 for key-on level detects both the synchronization level and the key-on level; however, no key or playback mechanism is assigned to count zero, so that no unwanted sounds are caused thereby. The resulting output, after buffering by the key-on driver 94, is the multiplexed playback key-on signal 60 which drives the transistor tree matrix 36 during playback. The clock threshold detector 88 provides an output for all three levels, thereby driving a playback clock signal 76 which can be used to operate the counter and gating circuits 38.
The three signals which are extracted from the playback signal 26 by the threshold detectors 42 (i.e., playback sync 78, playback clock 76 and multiplexed playback key-on 60) all bear the exact time relationship to one another that their counterpart signals (i.e., record sync 62, record clock 74, and multiplexed record key-on 58) bore during recording. Therefore, the same transistor switching matrix 36 functioning under the control of the same counter and gating circuits 38 can be used to produce the control signals which will ultimately cause the playing mechanisms 30 to function, each at the precisely correct time with respect to one another.
In the playback mode, each playback driver circuit 44 is routed to one input of transistor switching matrix 36. There is a plurality of playback driver circuits, i.e., one circuit for each electrically activated playing mechanism 30. Only one playback driver circuit 44 is shown in FIG. 2B. The capacitor 102 is charged to the supply voltage and transistor 104 is off during the normal quiescent condition when no action is desired from that particular mechanism. During playback, when a particular key is supposed to play, the key-on threshold detector 92 will detect a key-on level for that key at the proper count to which the key is assigned. A key-on logic level will therefore appear on the multiplexed playback key-on signal 60. The key-on driver circuit 94 will allow the matrix to rapidly conduct current and thus discharge capacitor 102 to ground, during only that particular count. Sufficient charge will be drained from capacitor 102 that the transistor 104 will change to a conducting state. The RC combination of 102 and 106 is designed such that transistor 104 will stay in conduction for slightly more than the time for one complete sampling frame, i.e., approximately 1/100th second if a 100 sample per second frame is used. This scheme allows the transistor 104 to remain conducting for as many consecutive frames as the particular key or control was held depressed by the musician during the recording process. When the key is supposed to go off, the threshold detector 92 will no longer detect a key-on level at the proper count. The transistor switching matrix 36 will therefore not be enabled to conduct current during that particular count. The capacitor 102 will charge through the transistor 104 emitter-base junction and resistors 106 and 108 causing transistor 104 to go OFF and remain OFF until the note is again called upon to play.
ORGAN EMBODIMENT
FIGS. 4 through 9 describe a specific embodiment which has been fabricated to test and demonstrate the performance capability of the system. This embodiment relates to a pipe organ, and provides the capability to record one complete 61 note organ manual plus two sets of expression shutters, or a total of 63 existing and controls. key or existing electropneumatic
Referring to FIG. 4, the existing organ console 110 contains the plurality of electrical switch contacts 96, one for each key and control. Through various existing switching circuits within the console, the signal associated with each key depression or shutter pedal movement ultimately appears at terminal board 112, at which point the wires to the existing windchest attachment The windchest 114 contains a plurality of electropneumatic relays 116 which perform the function of allowing air to enter the proper pipe when played. The existing expression shutters 1118 also contain electropneumatic relays 116 which control movement of air into sets of bellows which open or shut the shutters to affect volume control. Each of the electropneumatic relays 116, as illustrated in FIG. 4, is a solenoid. Fifteen volts DC is used by the existing system for an activating source.
The system is connected to the organ at terminal board 120. Transient suppression diodes 122 for each electrical contact prevent high transient voltages associated with interrupting electrical current to the highly inductive electropneumatic coils from damaging the system transistors. The multiconductor cable 32, 34 conducts the electrical key and control depression signals to the system during recording and the playback drive signals to the organ during playback.
The elements of this embodiment, though specifically sized to this system, are functionally identical to those previously described in the preferred embodiment. They consist of the transistor switching matrix 36, the counter and gating circuits 38, waveform generating circuits 40, playback threshold detectors 42, playback driver circuits 44, and associated interconnecting cables and switches. The recorder 24 is an existing home use audio tape recorder.
FIG. 5 illustrates the arrangement of assigning notes to the various counts. In the 64 count frame, count zero was used for synchronization, counts 2 through 62 for low C to high C, inclusive, and counts 1 and 62 for expression shutters. Four expression shutters are coupled to each of the two counts, thus eight total shutters can be controlled. A sampling frame of 621/2 frames per second is used, resulting in a 4,000 Hz. modulation waveform frequency. Because of the internal coupling arrangements within the existing organ console, it is possible to play from both manuals as well as the pedals. A total of four ranks of pipes can be selected by the stop tabs, thus allowing control by the system of a total of 244 pipes.
The elements of the system illustrated in FIG. 5 have been constructed as shown and described with reference to FIGS. 6-9. Of course, these elements are merely exemplary and could be embodied in many other forms, as indicated hereinafter.
The transistor switching matrix 36 is shown in FIG. 6. A total of 64 input transistors 98 accept the signals from the 63 key or shutter control contacts. The numerical value of each channel input corresponds to the count number in the sampling frame. The 64 input transistors are arranged in 16 groups of four each. Each group is further tiered into groups of four until, after three tiers, a single output is obtained. The gating pulses 56 from the counter circuits are applied directly to the bases of the transistors. The individual gating pulse designations shown in FIG. 6 are consistent with that shown in FIGS. 7A, 7B, and 7C, which shows the counter and gating circuits 38.
Referring to FIGS. 7A-7C, the binary counter 64 consists of six flip-flops 126 arranged to form a standard binary ripple counter capable of a counting sequence containing 64 counts, designated 0 through 63 , inclusive. The counter trigger pulses are 74 and 76, the record of playback clock pulses, respectively. The flip-flop outputs, designated A through F, are each routed to an inverting amplifier 128 to provide the necessary logical prime signals designated A through F. The AND gates 130 are arranged to provide a total of 12 gating pulse outputs. These are buffered by transistors 132 and then routed to the bases of the transistors in the transistor switching matrix 36 of FIG. 6. A positive voltage swing represents a logical true level on the gating pulse outputs. NAND gate 134, which generates the record sync pulse 62, is furnished the primed outputs from each counter stage, thus providing a negative-going sync pulse 62 only during count zero. The flip-flops 126, inverters 128, AND gate 130, and NAND gate 134 are all implemented with microminiature integrated circuits.
FIG. 8 illustrates the waveform generating circuits 40. The audio oscillator 80 consists of transistor 136 and the associated inductor 138, capacitor 140 and other components which connect to it. Transistor 142 forms an amplifier circuit to provide adequate signal level to operate the remaining circuits. The squaring circuit 82 uses three active circuits formed by transistors 144, 146, and 148 which provide the proper square wave rise times, and voltage levels suitable to drive the binary counter 64 of FIG. 7A. The key-on modulator circuit 84 functions to change the amplitude of the sine wave 86 on a per cycle basis, depending upon whether it is to represent sync level, key-on level, or clock level. The heart of the modulator is transistors 150, 152, 154 and 156. The remaining transistors 158 and 160 are used for buffering and inverting, respectively. At the emitter of 158 the highest level audio signal, i.e., sync level, is always present. However, transistors 150 and 152 are normally conducting when no sync or key-on pulses are present, thus a voltage divider is formed with resistors 162, 164, and 166. The audio signal therefore becomes attenuated to its lowest level, i.e., the clock level at the junction where 162, 164 and 166 are connected together.
To obtain the synchronization level, transistors 150 and 152 must be shut off. This occurs when the negative synchronization pulse 62 is applied during the count "zero." To obtain the key-on level, transistor 152 must be shut off. This occurs when a positive level is present on the multiplexed record key-on signal 58. Resistor 168 and capacitor 170 form an RC filter to eliminate spikes form the record signal 20 which may degrade the recording.
FIG. 9 shows the threshold detectors 42. Differential comparators 172, 174 and 176, implemented with integrated circuits, form the heart of the circuit. These devices provide an output logic true level when the input voltage at point A exceeds that on point B. The point B levels, therefore establish the threshold levels for detecting clock, sync, and key-on levels on the playback signal 26. The exact threshold levels are individually adjustable by potentiometers 178, 180 and 182. The playback signal 26 is buffered by transistor 184 and is applied to all three differential comparators. Transistors 186 and 188 form inverting and level shifting circuits for the playback clock 76 and playback sync 78 signals to produce proper signal levels for driving the counter circuits. Transistors 190 and 192 form the key-on driver circuit 94 which forms the multiplexed playback key-on signal 60. This signal connects to the transistor switching matrix 36 (FIG. 6).
OTHER APPLICATIONS
Remote Keyboard
Although the elements of this invention have been described as operating in a record and playback fashion, the identical elements can also be used in another potentially useful application, i.e., operation of remote keyboard(s). FIG. 10 illustrates the remote keyboard function. The keyboard inputs are processed identically to the manner previously described, except that the output of the key-on modulator 84 formerly designated the record signal 20 is now routed to a long line, i.e., a single pair of wires, rather than to the tape recorder. At the receiving end the threshold detectors 42' accept the signal 26', formerly designated the signal 26. The instrument playing mechanism 30' is thereby activated as previously described.
The remote keyboard application thus provides the capability to control a large plurality of instrument functions on a single pair of wires over any desired distance. It also allows any desired number of keyboards to share a single instrument playing mechanism. If the playing mechanism has an electronic audio output signal, such as an electronic organ, it can be routed on a pair of wires to the area where the keyboard performance is being initiated, and heard on a loudspeaker 194.
This scheme can also allow one performer to simultaneously play any desired number of instruments by providing the playback-type circuitry or each instrument.
KEYBOARD TRANSPOSITION AND COUPLING (UNIFICATION)
FIG. 11 shows a variation which allows the musician to (1) transpose the key signature of the selection being played back and (2) add additional tones at a desired interval (e.g., octave coupling, fifth coupling, etc.--also termed "unification" in the organ field).
Referring to FIG. 11, two sets of counter and gating circuits 38a and 38b are provided. These perform the same function as previously described, i.e., each set of counter and gating circuits 38a and 38b issues gating pulses 56 to the transistor switching matrix 36. By controlling the time position of the synchronization pulses to these counter and gating circuits 38a and 38b relative to the playback sync pulse 78, transposition and coupling will result. This is true provided that a sequential arrangement of assigning notes to counts, as shown in FIG. 5, is adhered to.
Transposition is implemented as follows (FIG. 11). The binary counter 64, identical to the counter in the counter and gating circuits 38 of FIG. 1, operates in conjunction with the transposition interval gates 196 to produce sync pulse 198. Sync pulse 198 causes the basic key signature to be transposed by one half-step for each count difference between sync pulse 198 and the occurrence of playback sync 78. This difference is established by the logical combination of binary counter outputs fed to the transposition interval gates 196. The interval can be made selectable by switch 200 by providing a gate 202 for each desired interval. When no transposition is desired, sync pulse 198 is made to occur simultaneously with the playback sync pulse 78.
The coupling (unification) function operates as follows. The counter and gating circuits 38b, synchronized by sync pulse 204, provides a second set of gating pulses 56 to the transistor switching matrix 36. The end result of the second-gating pulses is that an additional playback mechanism will be activated, i.e., an additional tone will be generated for each of the tones originally recorded. The second tone will differ in pitch from the original tone by one half-step for each count difference between sync pulses 198 and sync pulse 204. This difference is established by the coupling interval gates 206 and can also be made selectable by switch 208 by providing a gate 210 for each desired interval.
PIANO KEYBOARD EMBODIMENT
The basic embodiment described in FIGS. 1 through 3 is directly applicable to a piano insofar as recording and playing back the occurrences of key depressions is concerned. The expression or volume control aspect of the piano can also be implemented within the sequential sampling frame by: (1) allocating specific counts or channels to the task of volume control; (2) providing adequate sensing means to register the level information onto the recording waveform; and (3) providing playback activating means.
Another scheme, involving use of the second track of a two-track audio recorder is also feasible. In FIG. 12A, which depicts the recording mode, it is seen that the elements of the system required to record the occurrences of keys being depressed are identical to those previously described in FIGS. 1 through 3. The switch 96 consists of a standard organ-type key contact 212 placed under each key 214 and a standard contact block 216 mounted on the main console.
The additional elements, associated with recording of volume, include use of a volume modulator circuit 218, a separate track (designated channel 2) on the recorder 24, and a volume sensing device 222. The volume sensing device 222 produces a voltage proportional to the volume or loudness of the keys being played at any time. The configuration of the volume sensing device 222, though not specified herein, could, for example, consist of a manually activated potentiometer device, or it may consist of a more elaborate device which will sense velocity on the individual keys or hammers. Devices incorporating added, precisely spaced contacts on the contact blocks could also provide a means for sensing velocity of individual keys.
The key volume signal 224 is coupled to the volume modulator circuit, which creates an amplitude modulated sinusoidal waveform 220. The waveform, as shown in FIG. 12C need not be a multiplexed signal, as is the key-on record signal 20, because during the playback mode, only one playback driver is ever activated at a given instant.
FIG. 12B illustrates the playback function. The elements associated with defining the occurrences of key-on are identical to those previously described, except that the playback driver circuit 226 is modified. The volume driver circuit 228 detects the channel 2 volume signal 230 and provides a signal 232 to each of the playback drivers accordingly. Each playback driver circuit adjusts the voltage applied to each key activating solenoid 234 in accordance with the magnitude of the output signal 232 from the volume driver circuit 228.
ALTERNATIVES
Although the method and apparatus of this invention have been described with respect to a particular embodiment thereof, it should be clear to one skilled in the art that they could be implemented in many alternative ways without falling outside the scope or spirit of this invention.
For example, the logical functions involved, including counting and the assigning of keys or controls to specific counts, may be altered to fit any particular cost or functional requirement. In the embodiment of FIGS. 7A, 7B and 7C, the binary ripple counters therein could be replaced by shift register counters. The transistor tree matrix 36 of FIG. 6 could be replaced by a gating means in which a single-gating pulse is assigned to each count.
Likewise, the record signal 20 is shown to include an amplitude modulated sine wave. If appropriate circuitry can be provided, the method of this invention could also be implemented by phase modulation, for example. The selection of a waveform and a modulating technique is dependent upon the complexity of circuitry required to generate and detect the record signal 20, and the ability of the audio recorder 24 to accommodate the frequency spectrum of the record signal without significant distortion.
As previously indicated, the frequency of the recording waveform can be varied as long as a sufficiently high frame sampling rate is achieved such that no noticeable distortion occurs during playback. In the remote keyboard application of FIG. 10, a substantially higher frequency than that available for recording can be used because of the improved frequency response characteristics of a pair of electrical conductors as opposed to conventional audio recorders. With such applications, a significantly larger number of keys and controls can be included in the system.
Again with reference to the particular embodiments of FIGS. 5-9, the circuitry therein has not been optimized to achieve minimum hardware cost and maximum performance. It is not intended that the invention be limited to such circuitry and in fact, it would be desirable to add elements thereto which would make this system easier to operate by anyone. Such elements as an automatic gain control circuit for the record and playback signals, record and playback level meters, and others might well be included.
It is clear, then, that the invention, although having been described in terms of a preferred embodiment, is not to be limited thereto, and is in fact to be bounded only by the limits of the appended claims.