US 3859884 A
A tone generator particularly adapted for operation and performance as a musical instrument in which the shape of a cycle of sound is selected by a digital decoder which is adjustable to a sign amplitude values to digits of a reoccuring digital count, each reoccuring total count forming a complete cycle of sound.
Claims available in
Description (OCR text may contain errors)
nited States Patent 1191 Grable Jan. 14, 1975 TONE GENERATOR 3,358,068 12/1967 Campbell 1 84/1.03 x 3,515,792 6/1970 Deutsch 84/l.03 X [761 [memor- Rm 9 2414 Oakwood 3,610,799 10/1971 Watson 84/126 x Ave-a Huntsvllle, 35801 3,610,805 10/1971 Watson et a1 84/126 x 3,637,914 1/1972 Hiyama 84/103  1973 3,639,913 2/1972 Watson 84/101  Appl. No.: 333,666
Related Application Data Primary Examiner-Richard B. Wilkinson  Continuation-impart of Ser. No. 208,117, Dec. 15, ASslStam'Exammer U' Weldon 1971, abandoned.
 ABSTRACT  US. Cl 84/1.01, 84/1.03,84/1.26 51] 1111. C1. c1011 1/00 A tone generator Pamcularly adapted for Operauon  Field f Search 328/14; 5 34/101, and performance as a musical instrument in which the 34/103 L26 L23 shape of a cycle of sound is selected by a digital decoder which is adjustable to a sign amplitude values to  References Cited digits of a reoccuring digital count, each reoccuring UNITED STATES PATENTS total count forming a complete cycle of sound. 3,236,931 2/ 1966 7 Claims, 3 Drawing Figures Freeman 84/123 EXTERNAL SOURCE [41 3 47 I 29 39 u m... ..g 50. f A 4 p c1121 27 5 STAGE 2 Q 23 COUNTER 52 1 STAGE 32 /.,U FF 13m. 3w
19 29:: DEC. L 's3 35 1 11 v m 48 37 33b b [4811 71 57 4e 5-6 53 8 STAGE m SUM 5i BINARY L 67 e9 BSTAGE DECODER 1 5 1 7 COUNTER 1 9 65 TONE GENERATOR The present application is a continuation-in-part of an application by the applicant entitled Function Generator and bearing Ser. No. 208,117 filed Dec. 15, 1971 now abandoned.
BACKGROUND OF THE INVENTION This invention relates to digital function type tone generators and to their use to provide a novel electronic musical instrument.
It is a principal object of the invention to provide an improved function generator, suitable for various uses including that of a component of an electronic musical instrument, which has increased flexibility in the operators choice of details of the function to be generated. It is a further object of the invention to provide an electronic musical instrument employing such a digital function generator which has increased flexibility in the control of individual parameters of the sounds produced. It is an additional object of the invention to provide such an instrument which will produce high quality musical sounds and yet is inexpensive to manufacture and simple to operate;
SUMMARY OF THE INVENTION 7 An electronic function or tone generator according to the invention comprises a plurality of keys or similar actuation means and means responsive to the actuationof the keys for the generation of a sequence of a predetermined number of electrical impulses which are uniformly separated in time, the total elapsed time for the generation of the sequence being the period of a waveform corresponding to one of the keys. A plurality of adjustable resistors, equal in number to said predetermined number of impulses, are also provided as well as means interconnected with the set of resistors for applying the successive impulses of the sequence to the successive resistors of the set. An amplifier is connected to receive the adjusted and thus selected output from each resistor of the series and provides, together with a smoothing circuit, a musical output. In preferred embodiments, the function generator includes a second means for generating a second sequence of impulses, a second set of adjustable resistors equal in number to the number of impulses in the second sequence, and means connected to the resistors of the second set for applying successive impulses of the sequence to successive resistorsof the set. In this manner a second set of electrical outputs'are generated and these are applied to the amplifier to modulate the output of the amplifier in terms of attack.
Other objects, features, and advantages of the invention will appear from the following description of a preferred embodiment in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electrical schematic diagram of a function generator and electronic musical instrument constructed in accordance with this invention.
FIG. 2 is an electrical schematic diagram of a matrix switching system as contemplated by the invention.
FIG. 3 is a plan view of a musical instrument console as contemplated by'the invention.
Referring to the drawings, tuning control 11, is a positively biased variable resistor, which controls the bias voltage applied to upper contact a of double pole-single throw (D.P.S.T.) keyboard switches 13. Keyboard switches 13 are operated by depressing keys 15 (one switch per key) of keyboard 14 of console 16 (FIG. 3). When operated closed, an upper contact a of a switch 13 applies bias through tuning resistor 11 to a particularly adjusted variable resistor 17 which functions to adjust the input voltage to voltage controlled oscillator (V.C.O.) 19 and thus variable resistor 17 functions to adjust the frequency selected by a particular key, 15 and thereby the scale interval of the system. The lower contacts b of each switch 13 supplies a ground potential to the system as a logic signal as will be described below. As illustrated, keyboard 14 is a two octave keyboard with switches 13a and 13b representative of the first two key switches of one octave and switches 13c and 13d representative of the first two key switches of the second octave.
V.C.O. 19 generates a frequency 32 times the desired output frequency of the instrument as will be further explained. Its output or the output of an external frequency source 21, is selected by switch 23. The output frequency, which is fed to pulse generator 25, is converted therein to a square waveform of the same fre quency. The output of square wave pulses of pulse generator is fed to one input of AND gate 29 and to one or more frequency dividers 27 which selectively divide by, different factors (e.g., 2, 4, 8, etc.). Assuming a single divider 27, as shown, which divides by 2, its output is supplied to an input of and gate 29a. Octave select inputs for AND gates 29 and 29a are supplied from the lower contact b of each keyboard switch 13 by means of matrix switch 31 which includes a bus bar 33 common to keyboard switches of each keyboard octave. Thus, as shown, bus bar 33a is connected to the b contacts of switches 13a and 13b and bus bar 33b is connected to the b contacts of switches 13c and 13d and the rest of the switches of the same octave. Octave selection is achieved by means of sliding contact 35 on each bus bar through contacts 37 which selectively connects a given bus bar to the input of either AND gate 29 or 29a to provide either the output frequency of pulse generator 25 to five stage counter. 39 or onehalf of this frequency to counter 39. Five stage counter 39 is a binary counter which counts up to 32 and its counts appears on output leads 40 connected to binary decoder 41. Decoder 41 includes 32 switches, each controlled by one of the counts of counter 39. The
switches contacts (or output leads of electronic switches) are connected with one contact grounded and the other contact connected to one of timbre resistors 43. Each resistor 43 is in turn connected through a bias resistor 45 to a bias source. A slider 47 adjusts the value of each resistor 43. Thus decoder 41 internally grounds each resistor 43 in sequence as counter 39 counts to form a series of voltage dividers 48 with a common output 48a which is connected to one input of amplifier 49. Sliders 47 and thus resistors 43, are adjusted as, for example, illustrated in FIG. 3, to make up a cycle having a waveform of a desired shape. The cycle repeats each 32 counts to provide a final musical output frequency of the instrument which is one thirtysecond of the frequency of V.C.O. 19 (or other source 21). This final frequency is fed to input 48a of summing amplifier 49 and an attack effect signal is fed to the other input 65 of summingamplifier 49. This attack effect or envelope is developed as follows; A free-running multivibrator 51 generates a selected frequency determined by rate control 52, typically in a range of 8 to 80 hertz, and the signal is applied to the counting input of three stage binary counter 53 which counts up to 8. Binary counter 53 commences a count and counts 8 under the control of OR gate 65 in response to the depression of any key which applies a ground to an input of OR gate 65. Output terminals 54 from counter 53 are connected to 8 stage binary decoder 55 which functions' in the'manner described for decoder 41 to selectively ground an output terminal 56 as a particular count occurs. This results in the left side of attack resistors 57 being individually ground, in order, to provide, sequentially, selected output voltages at output point 59, depending upon the voltage division occurring between biased resistor 59 and a particular resistor 57.
Thus in the manner described above for producing the fundamental output frequency wave shape, an attack ing control 11 is adjusted when it is desired to change the key or frequency range of the entire keyboard.
Select switch 23 enables an external source 21 such as a frequency synthesizer to be used in place of V.C.O.
19 as the frequency source. Assuming that V.C.O. 19
crete voltage to V.C.O. 19. The frequency produced by the V.C.O. is fed through select switch 23 to pulse genenvelope shape is formed by sequential selection'of voltage dividers 56 composed of attack resistors 57 and bias resistor 59 as adjusted by sliders 61. The phase of the attack waveform is controlled by resetting counter 53 by the actuation of a keyboard switch through logic gate 65 using the logic signal described above. The amplitude of the attack envelope is controlled by attenuating resistor 63 which couples the output voltage at 59 to input 65 of summing amplifier49.
Thetone signal applied on input lead 48a to summing amplifier 49and attack signal applied to input 65 result in a composite attack shaped tone which is fed through volume control 67 to integrating amplifier 69. lntegrat ing amplifier 69 smoothes the signal with a degree of smoothness being controlled by feedback capacitor 71, which thus effects a tone control.
FIG. 2 shows an extension of matrix switch 31 to enable automatic sequential octave selection. An additional strip 73 is provided for each of the plurality of principle bus bars 33. This contact strip 73 is connected to the enable input of a binary decoder 75 which is similar in function to binary decoder 41 such that secondary bus bars 77 are selected in sequence in accordance with binary number from counter 79, driven'by multivibrator 81. The slider of the activated busselects the octave range applied to pulse counter 39 as before. The phase of the sequential octave selection is controlled by a reset signal from the keyboard analo- I bre resistors 43, are adjusted to create the desired timbre waveform. Similarly sliders 61, and thus attack resistors 57, are set to a desired attack modulation envelope. The rate and depth of the effect of the attack modulation envelope are set by controls 52 and 63, respectively. Sliders 35 of octave switch 31 are set to select the octave range to be produced at the output. Tone control 71 and volume control 67. are adjusted for desired mellowness and loudness, respectively. Scale interval resistors 17 are adjusted when it is desired to change the scale interval from a previous setting. Tunerator 25. The square wave output of pulse generator 25 is applied to AND .gate 29 and to flip-flop 2'7. The output of flip-flop 27 is fed to AND gate 29a. A bus bar 33b of matrix switch 31 is also activated through keyboard switch 13c by the depression of key 15 causing AND gate 29 to be gated and the output of pulse generator 25 to be directly applied to counter 39. The pulses of the square wave are counted by counter39 which sends its numbers to be decoded by decoder 41. The decoder 41 thus activates timbre resistors 43 in sequence in accordancewith the numbers from counter 39 and successive voltage levels are sent to input 48a of amplifier 49 Also when keyboard switch 13 is closed by key 15 counter 53 is'reset through gate 65. Counter 53 then counts pulses from'free running multivibrator 51 whose frequency has been adjusted by rate control v 52. Decoder 55 receives numbers from counter 53, and in accordance therewith activates attack resistors 57 in sequence. Thus a second sequence of voltages is presented through depth control 63 to input 65 of summing frequency generating means for selectively generat ing a selected frequency'and comprisingi actuating means for providing a selected electrical output,
oscillator means responsive to a said electrical output for generating a discrete frequency, and squaring circuit means responsive to theoutput frequency of said oscillator means for shaping the output frequency of said oscillator means and providing pulse output cycles as-the output of said frequency generating means; counting means responsive to the output of said frequency generating means for repetively counting a selected total count of output cycles of said frequency generating means, each repeated composite count constituting an output cycle of said counting means;
decoding means responsive to said counting means and each said count of an outputcycle of said generating means counted by said counting meansfor providing a selected output voltage for each discrete count of an output cycle of said generating means, said decoding means comprising:
a plurality of electrical circuits, each being adjustable and including means for providing a selected electrical output, and
switchingmeans responsive to each of said discrete counts of said counting means for providing as an output of said decoding means an electrical output to one of said electrical circuits,
whereby a said output cycle of said decoding means repeats after each said selected total count, and the shape of said output cycle of said decoding means corresponds to the composite of said selected electrical outputs.
2. A tone generator as set forth in claim 1 wherein said actuating means includes a plurality of switches coupled to a voltage source and said oscillator means responsive to the operation of a said switch for generating a said selected frequency and said tone generator further comprises: I
musical attack control means comprising a second switching means responsive to the operation of one of said switches and a counting means controlled by said second switching means to actuate a second decoding means for sequentially providing, at a selected rate, a plurality of output potentials; and summing means responsive to the output of said decoding means and said musical attack control means for providing a musical output which conforms to the output of said decoding means as modulated by the output of said musical attack control means. 3. A tone generator as set forth in claim 2 further comprising integration means responsive to the output of said summing means for providing a smoothed tonal output. I
4. A tone generator as set forth in claim 1 wherein said frequency generating means includes a plurality of switches and said tone generator further comprises:
octave control means for providing an octave control signal;
at least one frequency divider responsive to an output of said frequency generating means for providing an output at a selected lower frequency than the means to said counting means and a second gating circuit means responsive to a control signal for interconnecting the output of a said frequency di-- vider to said counting means; and
octave switching means responsive to said octave control signal and including means for selectively providing a said control signal to one of said gating circuits, whereby either the fundamental frequency output of said frequency generating means or a selected lower frequency is applied to said counting means.
5. A tone generator as set forth in claim 4 wherein said octave control means comprises means for sequentially supplying said control signal to different of said gating circuits, whereby a plurality of octave related tones are sequentially obtained.
6. A tone generator as set forth in claim 4 wherein said octave control means comprises a matrix switch having a plurality of conductive cross bars and means for selectively interconnecting between particular said said variable resistor.