BACKGROUND OF THE INVENTION
Various devices have been proposed or utilized in the past for providing some type of visual display indicative of the state of tune of a musical instrument. Such devices ordinarily have employed various mechanical or electro-mechanical devices and have been relatively large and unwieldy and, as well, require a relatively large power input. Also, it is usual to require a relatively long warming up period before such devices have stabilized sufficiently well to perform their intended function.
It would be desirable, however, to provide a small, portable and self-sufficient tuning device for musical instruments which could be switched on or off instantaneously and which could be immediately used for tuning purposes.
BRIEF SUMMARY OF THE INVENTION
It is, accordingly, of primary concern in connection with the present invention to provide an electronic device, self-contained tuning device for musical instruments, and which includes an array of indicator devices for visually indicating the state of tune of a musical instrument. The operation of the device is such that the indicator devices of the array are energized sequentially in one direction when the tone of an associated musical instrument is sharp, the display devices are energized sequentially in the opposite direction when the tone is flat, and wherein a stationary display is produced when the musical instrument is in pitch, the stationary display being characterized by the periodic energization of one of the display devices.
Basically, the circuit according to the present invention embodies a sequencing means which accepts two inputs, both of pulse train form, one of which is produced by a pulse generator means and the other of which is produced by a converter which accepts the frequency content of the tone produced by the musical instrument. When the musical instrument is in pitch with the tuning device, the prfs (pulse repetition frequencies) of the two pulse train outputs noted are harmonically related such that the aforesaid stationary display is provided, one of the pulse train outputs sequentially enabling the individual visual display devices and the other of the pulse train outputs energizing a selected visual display device provided that coincidence exists between the two pulse train outputs.
Preferably, the pulse train output of the pulse generating means is the nth harmonic of the fundamental tone where n is equal to the number of display devices.
Of particular importance in connection with the present invention is the provision of a converter in the aforesaid combination wherein the converter is in the form of a phase lock loop. This type of arrangement is especially effective for the purposes intended inasmuch as it will operate in the presence of substantial background noise and will operate effectively irrespective of frequency content of the musical instrument producing the tone under test. That is to say, the loop can equally as well lock onto the fundamental, a subharmonic or a harmonic thereof without change in operation of the device and will therefore accommodate to a musical instrument whether same produces essentially a fundamental tone, is enriched in harmonics with suppressed fundamental, etc.
The pulse generating means according to the present invention is also of importance in that by programmable coding techniques, a highly stable crystal oscillator produces the single reference frequency and dividing techniques are employed to produce, selectively, the reference pulse train output whose prf pulse repetition frequency is of the correct frequency for the tone under consideration.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a perspective view showing a device constructed according to the present invention and illustrating the general mechanical layout thereof;
FIG. 2 is a block diagram illustrating in simplified fashion the basic principles according to the invention;
FIG. 3 is a block diagram illustrating the pulse generator reference means inclusive of the coding technique employed for producing the desired output pulse train prf;
FIG. 4 is a block diagram illustrating the principles of the converter means and of the sequence switching means according to this invention; and
FIG. 5 is a circuit diagram illustrating a preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring at this time more particularly to FIG. 1, the tuning device according to the present invention and in its preferred form will be seen to include a suitable case or housing 12 within which the battery source of power and the electronic circuitry are housed and mounting an array of indicator devices 14, 16, 18, 20, 22, 24, 26 and 28. A selectivity control knob 30 is provided as is a tone selector knob 32 and there is also provided an on-off switch 34. A suitable receptacle at the side of the casing 12 accepts the jack 36 of a flexible cable 38 to which the pick-up microphone 40 is attached, substantially as is shown.
According to the objects of this invention, the casing 12 is of pocket-size dimensions or less and is completely self-contained to include all of the electronic circuitry and the power source in the form of a battery or batteries as well.
In operation, the device functions to produce different kinds of displays at the light producing devices 14-28 which indicate the state of tune of the musical instrument whose tone is picked up by the microphone 40. Specifically, when the tone of the instrument is sharp or flat, the indicator lights or display devices 14-28 will sequentially glow or be energized either from the left to right as viewed in FIG. 1 or from the right to the left as viewed in FIG. 1. As the display moves in one direction, the indication informs the user that the musical instrument is flat whereas when the display moves in the opposite direction, the operator is informed that the musical instrument is sharp. On the other hand, when the display is stationary and only one of the indicator devices 14-28 repetitively lights up, the user is apprised that the musical instrument is in pitch. The rate at which the display sequences in either of the opposite directions is indicative of the degree by which the musical instrument is sharp or flat and, if desired, the selectivity switch hereinafter described may be actuated by means of the knob 30 either to increase or decrease the rate of display device sequencing. Typically, the reference pitch may be adjusted by the knob 32 to select any one of the diotonic notes of a major scale, as for example the C major scale, so as to accommodate for the tuning requirements of various instruments. Obviously, any other desired arrangement may be utilized with respect to the reference pitch.
The basic principles according to the present invention will be seen readily from a study of FIG. 2 wherein it will be noted that the reference generator means indicated by the reference character 42 produces a pulse train output signal at the conductor 44 which is applied to one input terminal of the sequencing switching means 46. The microphone 40 is connected to the converter means 48 which produces a second pulse train output at the conductor 50 which is applied to the other input terminal of the sequencing switching means 46. The means 46 forms part of the display means together with the individual visual indicator devices 52, 54, 56 and 58. Whereas eight indicator devices are illustrated in FIG. 1 and only four are illustrated in FIG. 2, it will be appreciated that any number of indicating devices greater than two may be utilized to perform the functions of the present invention.
When the musical instrument under test is producing the correct tone, the pulse train outputs at the conductors 44 and 50 are harmonically related and one of these signals is utilized sequentially to enable the indicators 52, 54, 56 and 58 while the other of these pulse train outputs is utilized to energize that single indicator 52-58 which is enabled in consonance with the prf of such other pulse train output. Thus, when the musical instrument is flat and a correspondingly different prf is present at its output 50, the indicators 52-58 will be energized sequentially in one direction whereas if the musical instrument is sharp, the indicators will be sequentially energized in the opposite direction.
In order to provide the requisite waveform at the output conductor 44 of the reference generator means 42 and, as well, to accommodate for tuning to different pitches, the reference generator means is constructed according to FIG. 3. As shown, the reference generator means includes a highly stable crystal oscillator source 60 which is utilized such that its stable frequency output at the conductor 62 clocks the counter 64. The counter 64 is of the type having a plurality of output lines 66, 68, 70, 72, 74, 76 and 78 at all of which logical ones appear when the counter has counted a full complement of the clock pulses and with the reset cycle occupying the next clock period. When the counter is full, logical ones appear at all of its output conductors 66-78 and these are ANDED by the gate 80 to produce a pulse of the pulse output train at the conductor 44 and, as shown, the counter is reset at this time. Thus, the counter 64 operates effectively to divide down the frequency of the fixed and stable oscillator 60 normally to produce an output at the conductor 44 which, in the particular instance shown, is 1/128 the frequency of the crystal oscillator 60 (127 counts to fill the counter 64 + one clock input for reset). To provide for pulse train outputs at the conductor 44 having different prfs in accord with the tuning range of the device, the coding techniques symbolically illustrated in FIG. 3 may be employed. Thus, the terminal 82 is connected to a source of voltage corresponding to the logical one condition and any one or a combination of the switches 84 may be actuated to place the logical one input on a corresponding output line 66-78 of the counter 64 so as to cause the counter to count to any selected and desired predetermined number at which time an output will appear at the conductor 44 to reset the counter as described hereinabove. As will be appreciated, the natural frequency of the oscillator 60 must therefore be selected high enough to accommodate all of the frequencies of interest by division with a whole number.
FIG. 4 illustrates symbolically not only the functioning of the converter means 48 but also of the sequence switching means 46. The converter means 48 is in the form of a conventional phase lock loop composed of a phase detector 86, a filter 88 and a voltage controlled oscillator 90.
As previously noted, the display means includes the sequence switching means 46 with the indicators 52, 54, 56 and 58 and having the two input terminals to which the conductors 44 and 50 are connected. As illustrated symbolically in FIG. 4, the conductor 44 is connected to the clock input of decoding counter 92 which provides successive logical one outputs at its output conductors 94, 96, 98 and 100 which are connected as individual inputs to the AND gates 102, 104, 106 and 108. The other inputs to the AND gates are provided in common from the conductor 50 as shown. Thus, one input to each AND gate is enabled sequentially from the decoder 92 and the other input to each of the AND gates is effective to energize the corresponding indicator 52, 54, 56 or 58 when coincidence of inputs appears at the respective AND gates. Thus, when the musical instrument is in pitch, the lower frequency input at the conductor 50 will always coincide with one and only one of the sequential enablings of the AND gates 102-108 and the corresponding one and only one indicator or display device 52-58 will periodically be energized to provide the stationary display. If the pulse output train frequency from the converter means 48 is of either higher or lower frequency than that at the reference conductor 44, sequential energization of the display devices 52-58 will occur, the direction of sequencing being dependent upon whether the musical instrument is sharp or flat with respect to the tuning device.
A preferred embodiment of the invention is illustrated in FIG. 5. The crystal 110 of the oscillator circuit 60 is chosen to produce a suitable frequency which for example may be 2.00024 MHz and provides the clock input for a nine bit counter 112 whereby basically to divide the frequency at the conductor 62 by 1024. As noted, the counter ignores a clock pulse while reset so that the binary number produced when all of the output lines to the counter 112 are logical ones (i.e.=1023) plus the additional clock pulse during reset equals the maximum division which can be performed by the counter 112. Instead of employing the switch arrangement 84 of FIG. 3, any suitable apparatus for performing a variable ANDing function may be utilized such as the coding disc 114 which performs the same function. Alternatively, one may use a custom coded diode matrix to perform a diode logic AND function. For example, Harris Semiconductor H 1-0186 8×6 custom coded diode matrices may be empolyed. The coding disc shown is simply rotated by the knob 32 correspondingly to condition the output lines of the counter 112 in accord with the division required, the logical one input being at the conductor 116. To provide the proper logic, the NAND gates 118, 120 and 122 are provided, all feeding the NOR gate 124 as shown. To illustrate the coding which is necessary, with the aforesaid frequency of the crystal 110 division by 239 generates 8369.21Hz corresponding to the C9 ; division by 253 generates B8, etc. and the eight diotonic tones of a C major scale may thus be generated by proper coding at the disc 114.
The microphone 40 drives a suitable current summing amplifier 126 and the output thereof is coupled to the non-inverting amplifier 128 and also to the inverting amplifier 130. The complementary signals appearing at the outputs 132 and 134 of these respective amplifiers are applied respectively to the MOS transistor switches 136 and 138. As illustrated, these switches are actuated in consonance with the output frequency of the voltage controlled oscillator 90 to pass the complementary signals of the amplifiers 128 and 130.
The converter or processor must cope with signals ranging in frequency from 70Hz, of widely varying mixture of am and fm components and the criteria of minimal size, cost and automatic operation obviate standard methods for converting the input at the microphone 40 to the suitable digital type signals required for operation of the device. A phase lock loop and the implementation thereof as shown in FIG. 5 is admirably suited to provide the proper functioning so as automatically to tune the vco 90 to the fundamental of the input frequency or of a harmonic or subharmonic thereof. The input signals from various sources are each a combination of many variables and the phase lock loop is capable of looking for and locking onto the only constant factor among them. Because the MOS transistor switches 136 and 138 pass the wave form unchanged to the following filter 88, and switch very rapidly, the phase detector is highly effective for dealing with signals of high noise or harmonic content. The vco used is voltage tunable from 60 Hz to 2300Hz to insure proper lock for inputs of 70-2100Hz and although its frequency range does not encompass the entire musical spectrum, notes outside this range will cause phase lock on a harmonic or submultiple frequency without affecting operation of the device.
Ignoring for the moment the two four bit counters 140 and 142, the pulse train outputs at the respective conductors 44 and 50 provide the inputs to the sequencing switching means as previously described. As described earlier, the counter 92 generates a sequential series of pulses at its output conductor 144. Each output conductor of the counter 92 feeds a bistable latch shown in FIG. 5 as accommodated in groups of four at 146 and 148. The latch clock inputs are connected to the output pulse train at the conductor 50 through the medium of the pulse forming circuit 150 providing at the output conductor 152 thereof pulse outputs of approximately one microsecond duration. The latches are effective on clock command input to store the information at their input and to retain such information after the clock level drops. The brevity of the pulses at 152 assures virtually instantaneous storage of the data yet the latches retain it until the next updating which allows a bright display from the light emitting diodes 154, 156, etc. without resorting to short high current drive pulses.
The two counters 140 and 142 are provided for the purpose of selectivity control and are associated with the respective switches 158 and 160 which are ganged for common actuation by the knob 30 (FIG. 1). These counters act simply as dividers to control the rate of sequencing of the display devices for a given off-pitch condition of the musical instrument. Thus, should the switches 158 and 160 be in the "1" position and the display devices flicker sequentially too rapidly, their rate may be slowed by switching to the "2" or to the "3" position. Thus, the "1" position represents the greatest sensitivity, etc. It will be appreciated of course that the light emitting display devices may be arranged in any desired array such as in a circle or otherwise as may be desired.