ANIMATION CIRCUIT FOR A MUSICAL INSTRUMENT
United States Patent 3694561
A plurality of tone generators respectively provide a fundamental frequency and even harmonics of the fundamental frequency to a first signal translating circuit of a musical instrument. The musical 12th or third harmonic, of the fundamental frequency is fed to a second transistor circuit which is interconnected with and shares a common output with the first transistor circuit so that the harmonics of the fundamental frequency beat with the added 12th signal component to obtain an animated effect, which simulates a nominally in-tune pair of vibrating strings. Simultaneous energization of the transistor circuits is provided by a control circuit which is responsive to a direct current keying voltage to render the transistor circuits operative to provide a percussive output envelope, and responsive to an alternating keying voltage to render the transistor circuits operative to provide a sustained output envelope.
US Patent References:
Electrical musical instrument
Williams - January 1939 - 2142580
Multifrequency generating and selecting system
Doelz - July 1948 - 2445664
ELECTRONIC MUSICAL INSTRUMENT FOR PRODUCING NOVEL ACOUSTIC EFFECTS FROM MULTITONE SIGNALS
Omura et al. - April 1970 - 3505461
Variable wave generator
Mahren - August 1949 - 2478973
Electric musical instrument
Wayne - September 1961 - 3000252
Electrical musical instrument
Williams - January 1939 - 2142580
Multifrequency generating and selecting system
Doelz - July 1948 - 2445664
ELECTRONIC MUSICAL INSTRUMENT FOR PRODUCING NOVEL ACOUSTIC EFFECTS FROM MULTITONE SIGNALS
Omura et al. - April 1970 - 3505461
Variable wave generator
Mahren - August 1949 - 2478973
Electric musical instrument
Wayne - September 1961 - 3000252
Application Number:
05/028668
Publication Date:
09/26/1972
Filing Date:
04/15/1970
View Patent Images:
Export Citation:
Assignee:
Chicago Musical Instrument Co. (Chicago, IL)
Primary Class:
Other Classes:
84/708, 984/309, 84/702
International Classes:
G10H1/02; G10H1/06; G10H1/04
Field of Search:
84/1.11,1.19,1.2,1.22,1.23,1.24,DIG.2,1.01,1.12,1.21,1.13,1.26 331/37,38,40
US Patent References:
| 3355539 | Sampling tone generator system for electronic organs | November 1967 | Munch et al. |
Primary Examiner:
Myers, Lewis H.
Assistant Examiner:
Witkowski, Stanley J.
Claims:
What I claim is
1. An animation circuit for a musical instrument, comprising:
2. An animation circuit according to claim 1, wherein each of said first and second transistor circuits each have a transistor which includes:
3. An animation circuit according to claim 2, wherein each of said first and second transistor circuits comprises:
4. An animation circuit according to claim 1, wherein said keying circuit comprises:
5. An animation circuit according to claim 4, wherein said rectifier and filter means comprises:
6. An animation circuit according to claim 5, wherein:
7. An animation circuit according to claim 1, wherein said keying circuit includes:
8. An animation circuit according to claim 1, wherein said keying circuit comprises
9. An animation circuit according to claim 1, wherein the animated output signal is proportional to the keying signal and wherein said keying circuit comprises:
10. An animation circuit according to claim 9, wherein said switch means comprises:
1. An animation circuit for a musical instrument, comprising:
2. An animation circuit according to claim 1, wherein each of said first and second transistor circuits each have a transistor which includes:
3. An animation circuit according to claim 2, wherein each of said first and second transistor circuits comprises:
4. An animation circuit according to claim 1, wherein said keying circuit comprises:
5. An animation circuit according to claim 4, wherein said rectifier and filter means comprises:
6. An animation circuit according to claim 5, wherein:
7. An animation circuit according to claim 1, wherein said keying circuit includes:
8. An animation circuit according to claim 1, wherein said keying circuit comprises
9. An animation circuit according to claim 1, wherein the animated output signal is proportional to the keying signal and wherein said keying circuit comprises:
10. An animation circuit according to claim 9, wherein said switch means comprises:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a circuit for reproducing tones in a musical instrument, and more particularly to a circuit for enriching a fundamental frequency by providing an animation of the fundamental frequency.
2. Description of the Prior Art
Heretofore, tone reproduction circuits for providing percussive output signals have generally included a circuit which is responsive to a direct current voltage to either open a gate for the output of an oscillator, or to energize an oscillator, for a certain interval of time. Such circuits are generally constructed and the components thereof dimensioned to provide either a percussive output envelope or a sustained level output envelope for the output of the oscillator; however, the content of these envelopes includes only the pure tone produced by the oscillator.
SUMMARY OF THE INVENTION
An animation circuit for a musical instrument employs a pair of transistor circuits for providing from standard pure electronically generated tones an output signal which includes a fundamental frequency and a plurality of changing harmonics thereof which effect an animation of the fundamental frequency. A first transistor circuit includes an input for receiving a first tone signal including the fundamental frequency and even harmonics of the fundamental frequency. The animation effect is provided by a second transistor circuit which is interconnected with the first transistor circuit and has an input terminal for receiving a second tone signal including the third harmonic of the fundamental frequency at a level of from 1:60 to 1:20 that of the first tone signal. The two transistor circuits share a common output whereat the harmonics of the fundamental frequency beat to provide a rolling or animated effect similar to that provided by two or three nominally in-tune piano strings which are struck by a piano hammer. The level range of 1:60 to 1:20 for the 12th with respect to the fundamental frequency defines the proportions wherein the animation is noticeable, but not so strong as to be undesirable, and the preferred ratio is 1:30 to provide animation that is felt and not necessarily heard.
A key switch of the musical instrument is selectively provided with either a direct current potential or an alternating current potential by a tab switch and circuit means are connected between the key switch and the transistor circuits for simultaneously enabling the transistor in response to either the direct current potential or the alternating current potential to provide an output envelope which is either percussive or non-percussive, respectively. The direct and alternating potentials are selectively applied to all key switches of the instrument so that the same key switch may utilize a single contact for playing the instrument in the percussive and non-percussive modes.
The frequency of the alternating current potential is in the range of from 1 -100 KHz, the preferred frequency being 40 KHz in that the frequencies above the audio range avoid modulation at the output, require small filtering elements, lie above the frequency response of the circuits so as to be ineffective if there is any leakage and provide a more linear attack slope or leading edge of the output envelope due to the better integration available at higher frequencies. Also, signals below 100 KHz do not present radiation problems.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invention will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic circuit diagram of an animation circuit for a musical instrument constructed in accordance with the principles of the present invention; and
FIG. 2 is a graphical illustration of a percussive envelope and a non-percussive envelope without attention to scale.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 there is illustrated an animation circuit which includes a pair of transistor circuits. A first of these transistor circuits comprises a transistor 10 having an emitter 11 which is connected to ground by way of a resistor 12. The emitter 11 serves as an input electrode for the first transistor circuit and is connected by way of a conductor 13 to a plurality of tone signal generating means 14, 15 and 16. A first generating means 14 provides a fundamental frequency f, a second generating means 15 provides the second harmonic 2f of the fundamental frequency and a third generator means 16 provides the fourth harmonic 4f of the fundamental frequency to the emitter electrode 11 of the transistor 10 by way of the conductor 13. The transistor 10 also includes a collector electrode 17 which is connected to a suitable biasing potential by way of an output terminal 18.
A second transistor circuit includes a transistor 19 having an emitter electrode 20 which serves as an input terminal for the second transistor circuit. The emitter electrode 20 of the transistor 19 is connected to ground by way of a resistor 21 and is connected to a fourth tone signal generating means 24 by way of a resistor 23. The fourth tone signal generating means provides the musical twelfth of the fundamental frequency, that is the third harmonic of the fundamental frequency based on an equitempered scale or three times the fundamental frequency, i.e. 3f. The transistor 19 also includes a collector 22 which is in common with the collector 17 of the transistor 10 to the output terminal 18.
The transistors 10, 19 have respective base electrodes 25, 26 which are connected together by a conductor 27 and connected to ground by way of a resistor 28. The two transistors 10, 19 are therefore normally conditioned non-conductive by virtue of the ground potentials appearing at their respective emitters and bases by way of the resistors 12, 21 and 28. The application of a positive potential at the respective bases 25, 26 of the transistors 10, 19 renders the transistors operative as transistor circuits and as amplifiers so that an output signal is provided at the output terminal 18, which output signal includes the base frequency f and a constant changing of harmonics of the base frequency due to the beat provided by the harmonics of the base frequency. The constantly changing harmonics provide a rolling or animated effect much like that obtained with a pair of nominally in-tune vibrating strings.
The transistor circuits are, as mentioned above, amplifier circuits. The signal amplification of these circuits is dependent upon the magnitude of the keying signal applied to the respective bases 25, 26; therefore, the transistor circuits may be utilized in different modes of operation to provide different envelopes for the output signal including a percussive envelope and a non-percussive envelope. Inasmuch as the animation circuit finds advantageous application in musical instruments having manually operated key switches, such as electronic pianos and organs, it is desirable that the various operational modes of the transistor circuits be made independent of the playing keys of an instrument and that selection means be provided to selectively determine the operational mode of the transistor circuits and provide the musician the flexibility of choosing at will his desired mode of operation. In order to accomplish the foregoing, a selection switch 30, such as a tab switch, is provided for selecting the type of keying signal which is to be provided to the translating circuits. The selection switch 30 includes a contact 31 which is connected to a direct current potential V, a contact 32 which is connected to an alternating current potential Vac, and a contact 33 which is connected in common to all of a plurality of key switches of the musical instrument. Here, the plurality of key switches is referenced 34 and is represented by an extended contact 35 for selectively contacting any of a plurality of other contacts 36-39. As illustrated in the drawing, the selection switch 30 is positioned to provide the direct current potential V to the switch contact 35 by way of the contacts 31, 33 of the selection switch 30. With the switches so connected, engagement of the contacts 35, 36 will render the transistor circuits operable to provide an output signal at the output terminal which includes the fundamental frequencies f animated by constantly changing harmonics thereof. The envelope of the output signal at the output terminal 18 will have the shape illustrated by the broken line A curve of FIG. 2.
The selection switch 30 and the key switches 34 form part of an keying circuit for providing the desired keying signal to the signal transistor circuits. The enabling circuit includes first circuit means for providing a transient enabling signal in response to the application of the direct current potential V to the switch contact 36 upon engagement of that contact by the switch contact 35. The first circuit means comprises a resistor 40 and a resistor 41 connected between the contact 36 and ground as a voltage divider. A capacitor 42 is connected by one of its terminals to the junction between the resistors 40, 41 and by another of its terminals to the anode of a diode 43. The cathode of the diode 43 is connected by way of a resistor 44 to the bases 25, 26 of the transistors 10, 19. The initial positive potential shift across the capacitor 42 is fed by way of the diode 43 and the resistor 44 to the bases 25, 26. A second capacitor 45 is connected between the cathode of the diode 43 and ground. As the capacitor 42 begins to charge, the capacitor 45 also begins to charge over a path including the capacitor 42 and the diode 43. The capacitor 42 charges rapidly and the rise in potential at the cathode of the diode 43 reverse biases the diode. This positive potential is also effective by way of a resistor 55 to forward bias a diode 52 connected to a snub bus 46. The snub bus 46 also has other diodes 53, 54 connected thereto for utilization by other animation circuits. The snub bus 46 is connected to a contact 51 of the selection switch 30, which is in turn connectable to the direct current potential V by way of a switch contact 49, or to a portion of that potential by way of a switch contact 50 which is connected to a tap of a potentiometer 47. The fast voltage rise at the cathode of the diode 43 and the conduction of the diode 52 is effective to provide a peak for the transient keying signal, which peak is effective to produce a corresponding peak of the envelope of the output signal as illustrated in the broken line curve A of FIG. 2.
The capacitor 45 is partially discharged through the snub circuit until the potential applied to the anode of the diode 52 is below the potential of the cathode of that diode. Further discharge of the capacitor 45 is over a first path including the resistor 44 connected to the bases 25,26 of the transistors 10, 19 and the base-emitter circuits of these transistors. This provides the decaying trailing edge of the envelope of the output signal.
A second discharge path for the capacitor 45 is available by way of a diode 63 having its anode connected to the capacitor 45 and its cathode connected to ground by way of a resistor 57 and contacts 59 and 60 of a switch 58. The switch 58 may be a pedal-operated sostenuto switch and include another contact 61 which is connected by way of a resistor 62 to a positive direct current potential. Operation of the switch 58 to engage the switch contact 59 with the switch contact 61 effects a reverse bias across the diode 63 to provide an extended decay of the charge on the capacitor 45. In addition, the cathode of the diode 63 is connected to ground potential by way of a resistor 56 and the resistor 41 which is effectively in parallel with the resistor 57. The trailing edge of the envelope of the output signal may therefore be controlled by controlling the rate of discharge of the capacitor 45 at levels below the snub decay of the keying signal.
A resistor 65 is connected between the junction of the capacitor 42 and the diode 43 and ground and provides an additional charging tap for the capacitor 42. A diode 64 is connected in shunt with the resistor 65 and poled to maintain the right-hand terminal of the capacitor 42 above ground potential.
The keying circuit also comprises second circuit means for providing a substantially constant level enabling signal for the transistor circuits. The second circuit means includes a number of components of the first circuit means means described above, which components function in a different manner with respect to an alternating current energizing signal. To operate in a non-percussive mode, the musician will operate the selection switch 30 to the position opposite that illustrated in FIG. 1 wherein the contact 32 engages the contact 33 and supplies an alternating current voltage to the contact 35 of the key switches 34. The alternating current voltage has a frequency in the range of from 1KHz-100KHz and is preferably above the audio range to prevent detrimental effects in the musical instrument in case of leakage of the alternating signal. Further, a high frequency signal is preferred to eliminate any possibility of modulation of the output signal. The alternating wave is also preferred to be non-sinusoidal and have an inward 50--50 power distribution for enhanced subsequent rectification and filtering.
The operation of a key switch to engage the contact 35, 36 presents the alternating wave across the voltage divider of the resistors 40, 41. The positive half cycle of the alternating wave is passed by the capacitor 42 to the anode of the diode 43 and by way of the diode 43 to the junction of the cathode of the diode 43, the capacitor 45, the resistor 44 and the resistor 55. The negative half cycle of the alternating wave is passed by way of the resistor 56 to the cathode of the diode 63 and then to the same junction as the positive half cycle of the alternating wave. At this junction, therefore, the alternating wave has undergone full wave rectification by the diodes 43, 63.
The positioning of the selection switch 30 for the non-percussive mode causes the contact 50 to disengage from the contact 51 and the contact 49 to engage with the contact 51 to place the direct current supply potential V on the snub bus 46 and, hence, on the cathode of the diode 52. The supply potential is relatively high with respect to the rectified alternating wave and is therefore effective to maintain the diode 52 in a reverse biased condition. The initial rapid decay of the percussive mode of operation is therefore eliminated in the non-percussive mode of operation.
The capacitor 45 functions to provide a filtering or smoothing integration of the rectified wave in cooperation with the high impedance now offered by the snubbing circuit and the smooth wave is applied by way of the resistor 44 as a substantially constant level keying signal to the respective bases 25, 26 of the transistors 10, 19. A capacitor 66 is connected to the bases 25, 26 of the transistors 10, 19 and provides a low impedance path to ground for any high frequency components in the enabling signal.
Upon release of the key switch and disengagement of the contacts 35, 36, the capacitor 45 discharges over the aforementioned discharge paths including the transistor circuits, the resistor 57 and the resistors 56 and 41. The discharge interval is, however, shorter in the non-percussive mode of operation in that the capacitor 45 does not obtain as great a charge as it does in the percussive mode of operation. The keying signal presented to the signal translating circuits has a trailing edge determined by the discharge of the capacitor 45, and the trailing edge is effective to provide a delay in the trailing portion of the envelope of the output signal as illustrated by the non-percussive envelope B of FIG. 2.
Referring specifically to FIG. 2, it is apparent that the signal components included within the percussive envelope A are constantly undergoing level changes as compared to the signal components included within the non-percussive envelope B in which the signal components are available for a substantial interval without any decay effect. Operation in the percussive mode therefore simulates the strike tone and damped vibratory oscillation of nominally in-tune strings and non-percussive operation causes an ensemble to be provided to a voice frequency to provide a chorus affect.
An animation circuit constructed as disclosed herein and as illustrated in FIG. 1 of the drawing employed a direct current potential of twenty volts, and alternating current voltage of 12 volts peak-to-peak at 40 KHz and NPN transistors in conjunction with the following tabulated values of circuit components.
Resistors (Ohms) Capacitors (Mfd.) ____________________________________________________________ ______________ 12 4.5K 42 0.27 21 35K 45 0.27 23 220K 66 0.01 28 See Note* 40,62 1K 41,55 100K 47 10K 56 50K 57 1M 65 500K ____________________________________________________________ ______________
while the invention has been disclosed with reference to a specific embodiment, many changes and modifications may become apparent to those skilled in the art without departing from the spirit and scope of the invention, and it is to be understood that I wish to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.
1. Field of the Invention
This invention relates to a circuit for reproducing tones in a musical instrument, and more particularly to a circuit for enriching a fundamental frequency by providing an animation of the fundamental frequency.
2. Description of the Prior Art
Heretofore, tone reproduction circuits for providing percussive output signals have generally included a circuit which is responsive to a direct current voltage to either open a gate for the output of an oscillator, or to energize an oscillator, for a certain interval of time. Such circuits are generally constructed and the components thereof dimensioned to provide either a percussive output envelope or a sustained level output envelope for the output of the oscillator; however, the content of these envelopes includes only the pure tone produced by the oscillator.
SUMMARY OF THE INVENTION
An animation circuit for a musical instrument employs a pair of transistor circuits for providing from standard pure electronically generated tones an output signal which includes a fundamental frequency and a plurality of changing harmonics thereof which effect an animation of the fundamental frequency. A first transistor circuit includes an input for receiving a first tone signal including the fundamental frequency and even harmonics of the fundamental frequency. The animation effect is provided by a second transistor circuit which is interconnected with the first transistor circuit and has an input terminal for receiving a second tone signal including the third harmonic of the fundamental frequency at a level of from 1:60 to 1:20 that of the first tone signal. The two transistor circuits share a common output whereat the harmonics of the fundamental frequency beat to provide a rolling or animated effect similar to that provided by two or three nominally in-tune piano strings which are struck by a piano hammer. The level range of 1:60 to 1:20 for the 12th with respect to the fundamental frequency defines the proportions wherein the animation is noticeable, but not so strong as to be undesirable, and the preferred ratio is 1:30 to provide animation that is felt and not necessarily heard.
A key switch of the musical instrument is selectively provided with either a direct current potential or an alternating current potential by a tab switch and circuit means are connected between the key switch and the transistor circuits for simultaneously enabling the transistor in response to either the direct current potential or the alternating current potential to provide an output envelope which is either percussive or non-percussive, respectively. The direct and alternating potentials are selectively applied to all key switches of the instrument so that the same key switch may utilize a single contact for playing the instrument in the percussive and non-percussive modes.
The frequency of the alternating current potential is in the range of from 1 -100 KHz, the preferred frequency being 40 KHz in that the frequencies above the audio range avoid modulation at the output, require small filtering elements, lie above the frequency response of the circuits so as to be ineffective if there is any leakage and provide a more linear attack slope or leading edge of the output envelope due to the better integration available at higher frequencies. Also, signals below 100 KHz do not present radiation problems.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invention will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic circuit diagram of an animation circuit for a musical instrument constructed in accordance with the principles of the present invention; and
FIG. 2 is a graphical illustration of a percussive envelope and a non-percussive envelope without attention to scale.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 there is illustrated an animation circuit which includes a pair of transistor circuits. A first of these transistor circuits comprises a transistor 10 having an emitter 11 which is connected to ground by way of a resistor 12. The emitter 11 serves as an input electrode for the first transistor circuit and is connected by way of a conductor 13 to a plurality of tone signal generating means 14, 15 and 16. A first generating means 14 provides a fundamental frequency f, a second generating means 15 provides the second harmonic 2f of the fundamental frequency and a third generator means 16 provides the fourth harmonic 4f of the fundamental frequency to the emitter electrode 11 of the transistor 10 by way of the conductor 13. The transistor 10 also includes a collector electrode 17 which is connected to a suitable biasing potential by way of an output terminal 18.
A second transistor circuit includes a transistor 19 having an emitter electrode 20 which serves as an input terminal for the second transistor circuit. The emitter electrode 20 of the transistor 19 is connected to ground by way of a resistor 21 and is connected to a fourth tone signal generating means 24 by way of a resistor 23. The fourth tone signal generating means provides the musical twelfth of the fundamental frequency, that is the third harmonic of the fundamental frequency based on an equitempered scale or three times the fundamental frequency, i.e. 3f. The transistor 19 also includes a collector 22 which is in common with the collector 17 of the transistor 10 to the output terminal 18.
The transistors 10, 19 have respective base electrodes 25, 26 which are connected together by a conductor 27 and connected to ground by way of a resistor 28. The two transistors 10, 19 are therefore normally conditioned non-conductive by virtue of the ground potentials appearing at their respective emitters and bases by way of the resistors 12, 21 and 28. The application of a positive potential at the respective bases 25, 26 of the transistors 10, 19 renders the transistors operative as transistor circuits and as amplifiers so that an output signal is provided at the output terminal 18, which output signal includes the base frequency f and a constant changing of harmonics of the base frequency due to the beat provided by the harmonics of the base frequency. The constantly changing harmonics provide a rolling or animated effect much like that obtained with a pair of nominally in-tune vibrating strings.
The transistor circuits are, as mentioned above, amplifier circuits. The signal amplification of these circuits is dependent upon the magnitude of the keying signal applied to the respective bases 25, 26; therefore, the transistor circuits may be utilized in different modes of operation to provide different envelopes for the output signal including a percussive envelope and a non-percussive envelope. Inasmuch as the animation circuit finds advantageous application in musical instruments having manually operated key switches, such as electronic pianos and organs, it is desirable that the various operational modes of the transistor circuits be made independent of the playing keys of an instrument and that selection means be provided to selectively determine the operational mode of the transistor circuits and provide the musician the flexibility of choosing at will his desired mode of operation. In order to accomplish the foregoing, a selection switch 30, such as a tab switch, is provided for selecting the type of keying signal which is to be provided to the translating circuits. The selection switch 30 includes a contact 31 which is connected to a direct current potential V, a contact 32 which is connected to an alternating current potential Vac, and a contact 33 which is connected in common to all of a plurality of key switches of the musical instrument. Here, the plurality of key switches is referenced 34 and is represented by an extended contact 35 for selectively contacting any of a plurality of other contacts 36-39. As illustrated in the drawing, the selection switch 30 is positioned to provide the direct current potential V to the switch contact 35 by way of the contacts 31, 33 of the selection switch 30. With the switches so connected, engagement of the contacts 35, 36 will render the transistor circuits operable to provide an output signal at the output terminal which includes the fundamental frequencies f animated by constantly changing harmonics thereof. The envelope of the output signal at the output terminal 18 will have the shape illustrated by the broken line A curve of FIG. 2.
The selection switch 30 and the key switches 34 form part of an keying circuit for providing the desired keying signal to the signal transistor circuits. The enabling circuit includes first circuit means for providing a transient enabling signal in response to the application of the direct current potential V to the switch contact 36 upon engagement of that contact by the switch contact 35. The first circuit means comprises a resistor 40 and a resistor 41 connected between the contact 36 and ground as a voltage divider. A capacitor 42 is connected by one of its terminals to the junction between the resistors 40, 41 and by another of its terminals to the anode of a diode 43. The cathode of the diode 43 is connected by way of a resistor 44 to the bases 25, 26 of the transistors 10, 19. The initial positive potential shift across the capacitor 42 is fed by way of the diode 43 and the resistor 44 to the bases 25, 26. A second capacitor 45 is connected between the cathode of the diode 43 and ground. As the capacitor 42 begins to charge, the capacitor 45 also begins to charge over a path including the capacitor 42 and the diode 43. The capacitor 42 charges rapidly and the rise in potential at the cathode of the diode 43 reverse biases the diode. This positive potential is also effective by way of a resistor 55 to forward bias a diode 52 connected to a snub bus 46. The snub bus 46 also has other diodes 53, 54 connected thereto for utilization by other animation circuits. The snub bus 46 is connected to a contact 51 of the selection switch 30, which is in turn connectable to the direct current potential V by way of a switch contact 49, or to a portion of that potential by way of a switch contact 50 which is connected to a tap of a potentiometer 47. The fast voltage rise at the cathode of the diode 43 and the conduction of the diode 52 is effective to provide a peak for the transient keying signal, which peak is effective to produce a corresponding peak of the envelope of the output signal as illustrated in the broken line curve A of FIG. 2.
The capacitor 45 is partially discharged through the snub circuit until the potential applied to the anode of the diode 52 is below the potential of the cathode of that diode. Further discharge of the capacitor 45 is over a first path including the resistor 44 connected to the bases 25,26 of the transistors 10, 19 and the base-emitter circuits of these transistors. This provides the decaying trailing edge of the envelope of the output signal.
A second discharge path for the capacitor 45 is available by way of a diode 63 having its anode connected to the capacitor 45 and its cathode connected to ground by way of a resistor 57 and contacts 59 and 60 of a switch 58. The switch 58 may be a pedal-operated sostenuto switch and include another contact 61 which is connected by way of a resistor 62 to a positive direct current potential. Operation of the switch 58 to engage the switch contact 59 with the switch contact 61 effects a reverse bias across the diode 63 to provide an extended decay of the charge on the capacitor 45. In addition, the cathode of the diode 63 is connected to ground potential by way of a resistor 56 and the resistor 41 which is effectively in parallel with the resistor 57. The trailing edge of the envelope of the output signal may therefore be controlled by controlling the rate of discharge of the capacitor 45 at levels below the snub decay of the keying signal.
A resistor 65 is connected between the junction of the capacitor 42 and the diode 43 and ground and provides an additional charging tap for the capacitor 42. A diode 64 is connected in shunt with the resistor 65 and poled to maintain the right-hand terminal of the capacitor 42 above ground potential.
The keying circuit also comprises second circuit means for providing a substantially constant level enabling signal for the transistor circuits. The second circuit means includes a number of components of the first circuit means means described above, which components function in a different manner with respect to an alternating current energizing signal. To operate in a non-percussive mode, the musician will operate the selection switch 30 to the position opposite that illustrated in FIG. 1 wherein the contact 32 engages the contact 33 and supplies an alternating current voltage to the contact 35 of the key switches 34. The alternating current voltage has a frequency in the range of from 1KHz-100KHz and is preferably above the audio range to prevent detrimental effects in the musical instrument in case of leakage of the alternating signal. Further, a high frequency signal is preferred to eliminate any possibility of modulation of the output signal. The alternating wave is also preferred to be non-sinusoidal and have an inward 50--50 power distribution for enhanced subsequent rectification and filtering.
The operation of a key switch to engage the contact 35, 36 presents the alternating wave across the voltage divider of the resistors 40, 41. The positive half cycle of the alternating wave is passed by the capacitor 42 to the anode of the diode 43 and by way of the diode 43 to the junction of the cathode of the diode 43, the capacitor 45, the resistor 44 and the resistor 55. The negative half cycle of the alternating wave is passed by way of the resistor 56 to the cathode of the diode 63 and then to the same junction as the positive half cycle of the alternating wave. At this junction, therefore, the alternating wave has undergone full wave rectification by the diodes 43, 63.
The positioning of the selection switch 30 for the non-percussive mode causes the contact 50 to disengage from the contact 51 and the contact 49 to engage with the contact 51 to place the direct current supply potential V on the snub bus 46 and, hence, on the cathode of the diode 52. The supply potential is relatively high with respect to the rectified alternating wave and is therefore effective to maintain the diode 52 in a reverse biased condition. The initial rapid decay of the percussive mode of operation is therefore eliminated in the non-percussive mode of operation.
The capacitor 45 functions to provide a filtering or smoothing integration of the rectified wave in cooperation with the high impedance now offered by the snubbing circuit and the smooth wave is applied by way of the resistor 44 as a substantially constant level keying signal to the respective bases 25, 26 of the transistors 10, 19. A capacitor 66 is connected to the bases 25, 26 of the transistors 10, 19 and provides a low impedance path to ground for any high frequency components in the enabling signal.
Upon release of the key switch and disengagement of the contacts 35, 36, the capacitor 45 discharges over the aforementioned discharge paths including the transistor circuits, the resistor 57 and the resistors 56 and 41. The discharge interval is, however, shorter in the non-percussive mode of operation in that the capacitor 45 does not obtain as great a charge as it does in the percussive mode of operation. The keying signal presented to the signal translating circuits has a trailing edge determined by the discharge of the capacitor 45, and the trailing edge is effective to provide a delay in the trailing portion of the envelope of the output signal as illustrated by the non-percussive envelope B of FIG. 2.
Referring specifically to FIG. 2, it is apparent that the signal components included within the percussive envelope A are constantly undergoing level changes as compared to the signal components included within the non-percussive envelope B in which the signal components are available for a substantial interval without any decay effect. Operation in the percussive mode therefore simulates the strike tone and damped vibratory oscillation of nominally in-tune strings and non-percussive operation causes an ensemble to be provided to a voice frequency to provide a chorus affect.
An animation circuit constructed as disclosed herein and as illustrated in FIG. 1 of the drawing employed a direct current potential of twenty volts, and alternating current voltage of 12 volts peak-to-peak at 40 KHz and NPN transistors in conjunction with the following tabulated values of circuit components.
Resistors (Ohms) Capacitors (Mfd.) ____________________________________________________________ ______________ 12 4.5K 42 0.27 21 35K 45 0.27 23 220K 66 0.01 28 See Note* 40,62 1K 41,55 100K 47 10K 56 50K 57 1M 65 500K ____________________________________________________________ ______________
while the invention has been disclosed with reference to a specific embodiment, many changes and modifications may become apparent to those skilled in the art without departing from the spirit and scope of the invention, and it is to be understood that I wish to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.