System for generating tone source waveshapes

Abstract

The system comprises a frequency number memory device for storing information regarding the frequencies of respective tones, a keyboard switch for reading out frequency number information corresponding thereto from the memory device, an address generator including an adder for adding a predetermined number of the frequency number information thereby producing an address signal consisting of plural bits, address composers for processing the bits of the address signal and thereby composing digital tone signals constituting a saw-tooth, square and triangular waveshape, and digital-analog converters for converting the digital tone signals into analog tone signals, which are thereafter used to synthesize waveshapes of any tone.

Description

This is a continuation of application Ser. No. The address composer means does not utilize a waveshape memory for this digital waveshape composition. This is done by digital logic circuitry means for forming sample point amplitude values, without the use of a waveform memory, by manipulation of the digital address values qF themselves. In the following, a method of forming an attack-decay envelope for these data will be described.

The closure of a key-actuated switch in the keyboard switch circuit 1 is detected by an attack-decay logic circuit 9 (FIGS. 1 and 7). In response to the signal representing the closure of the keyboard switch and the output from an attack-decay oscillator 10, the attack-decay logic circuit 9 produces an address signal for reading the data out of an attack-decay memory 8 which stores digital information regarding the contour of an attack-decay envelope. In response to the address signal generated by the attack-decay logic circuit 9 the data regarding the attack envelope are read from the attack-decay memory 8 during a suitable interval following the closure of the keyboard switch. The intervals of attack and decay are controlled by the attack-decay oscillator 10. These data are applied to multiliers M₁, M₂ and M₃ for multiplying with the digital data regarding respective note source waveshapes applied from waveshape address composers 5, 6 and 7. Even after termination of the attack, while the keyboard switch is held closed, the terminal values of the attack envelope are read out. When the attack-decay logic circuit 9 detects the opening of the keyboard switch, the data regarding a decay envelope is read from the attack-decay memory 8 in the same manner as in the case of the attack envelope and these read out data are applied to the multipliers M₁, M₂ and M₃ for multiplying the digital data regarding the tone source waveshapes.

Stated more specifically, upon depression of any key, an ON signal is applied to one input of the lower AND gate AND 1 which causes the ATTACK OSC 10a. to produce an output pulse. This pulse is applied to the ATTACK DECAY COUNTER via the lower AND gate AND 1 and the OR gate. The ATTACK DECAY COUNTER then performs a binary counting operation and its count output is applied to the attack decay memory 8. In the meantime, the output "0" of the inverter is applied to one input of the other AND gate AND 2 whereby the pulse of the DECAY OSC. is inhibited and not applied to the ATTACK DECAY COUNTER. Upon release of the key, an OFF signal "0" is applied to the lower AND gate AND 1 so that it does not gate out the output pulse of the ATTACK OSC. Since the output of the inverter meanwhile becomesa "1," the output pulse of the DECAY OSC. is applied to the ATTACK DECAY COUNTER via said other AND gate AND 2 and the OR gate and is counted. When decay has finished, all inputs to the NAND circuit becomes "1" so that the DECAY FINISH signal becomes "0" and said other AND gate AND 2 ceases to gate out the output pulse of the DECAY OSC.

The digital data regarding the tone source waveshapes which have been multiplied by the amplitude coefficients from the attack-decay memory 8 in the multipliers M₁, M₂ and M₃, respectively, are applied to buffer memories B₁, B₂ and B₃ for equalizing the fluctuations in time. The outputs from the buffer memories B₁, B₂ and B₃ are sent to digital-analog converters C₁, C₂ and C₃, respectively, and converted into analog signals therein. In this manner, the three types of tone source waveshapes namely a saw-tooth wave, duty variable square wave and triangular wave are produced as analog signals.

Although the foregoing description has been made with reference to a monophonic instrument, it will be clear that tone source waveshapes for a polyphonic instrument can also be formed in the same manner. Furthermore, it should be understood that the clock signals applied to the address generator 4 and the address composer 5, 6 and 7 are generated by the single master oscillator 11. Consequently, it is possible to obtain extremely stable tone source waveshapes.

By analog processing the digitally represented tone source waveshapes produced in the manner described hereinabove it is possible to synthesize almost all musical tone waveshapes. It is also possible to use these tone source waveshapes as the fundamental waves in a compound tone synthesizer. Thus, according to this invention, it is possible to digitally form highly accurate and stable tone source waveshapes with a small size apparatus operating at a low frequency without using any waveform memory device and without the necessity of synthesizing higher harmonic components.

Claims

1. A system for generating tone source waveshapes comprising a pre-loaded frequency number memory device which stores in digital representation a plurality of frequency numbers corresponding respectively to the fundamental frequencies of the notes of said waveshapes; a keyboard switch circuit having a key-actuated switch for each of said notes for reading out a frequency number respectively corresponding thereto from said frequency memory device; an address generator responsive to the frequency number read out from said frequency memory device for producing a given number of successive address signals periodically, each address signal consisting of a plurality of bits; at least one address composer connected to receive said successive address signals from said address generator directly and responsive to a predetermined number of said plurality of bits of each address signal in the range from one bit to n bits, where n is more than one and less not more than the bit plurality, for digitally composing a tone waveshape having a fundamental frequency corresponding to said read out frequency number with an amplitude versus time characteristic determined by the digital word value of each predetermined number of address signal bits to which said one address composer responds; and means for converting the digitally composed tone waveshape into an analog equivalent thereof.

2. The system according to claim 1 wherein said address generator includes an adder for successively adding the read-out frequency number to itself and a buffer memory for storing the accumulated frequency number resulting from the successive addition performed by said adder.

3. The system according to claim 2 wherein said buffer memory stores said accumulated frequency number in the form of a plurality of bits, and said address composer comprises a buffer memory for storing a predetermined number of bits counting from the most significant bit in said address signal, thereby producing a saw-tooth wave.

4. The system according to claim 1 wherein said address composer is a duty variable square wave address generator.

5. The system according to claim 2 wherein said buffer memory stores said accumulated frequency number in the form of a plurality of bits and said address composer includes inverter means connected to receive only the most significant bit of said address signal, thereby producing a symmetrical square wave.

6. The system according to claim 2 wherein said buffer memory stores said accumulated frequency number in the form of a plurality of bits and said address composer comprises an AND gate circuit connected to receive the most significant bit of said address signal and a bit which is one bit less significant than said most significant bit, and inverter means responsive to the output of said AND gate circuit, thereby producing an asymmetrical square wave.

7. The system according to claim 2 wherein said buffer memory stores said accumulated frequency number in the form of a plurality of bits and wherein said address composer comprises a second buffer memory connected to receive a predetermined number of bits counting from the most significant bit in the address signal, inverter means, a selector for applying said predetermined number of the bits except the most significant bit and the bit which is one bit less significant than said most significant bit directly to and through said inverter means to said selector, means for controlling said selector in accordance with said bit which is one bit less significant than said most significant bit, complementing means responsive to the output from said selector for forming a two's complement, and means for controlling said complementing means in accordance with said most significant bit, thereby forming a triangular wave.

8. The system according to claim 1 which further comprises an attack-decay oscillator, an attack-decay logic circuit responsive to a signal indicating the operation of said key-actuated switch and the output from said attack-decay oscillator for producing an address signal, an attack-decay memory device storing information regarding attack and decay envelopes and connected to receive said the address signals signal from the attack/decay logic circuit for producing said attack and decay envelope information, and a multiplier connected between said address composer and said digital-analog converting means for multiplying said digital tone signal by said attack and decay envelope information.

9. In an electronic musical instrument having note selection keys, a system for generating tone source waveshapes comprising:

key identification means having a key-actuated switch for each note for generating a key identification signal corresponding thereto;

address generator means responsive to the key identification signal for producing a given number of successive address signals periodically, each address signal consisting of a plurality of bits;

address composer means connected to receive said successive address signals from said address generator means, and responsive to a predetermined number of said plurality of bits of each address signal in the range from one bit to n bits where n is more than one and not more than the bit plurality, for digitally composing a tone waveshape having a fundamental frequency corresponding to said generated key identification signal with an amplitude versus time characteristic determined by the digital word value of each predetermined number of address signal bits to which said address composer means responds, said address composer means not utilizing a waveshape memory for said digital waveshape composition; and

means for converting the digitally composed tone waveshape into an analog equivalent thereof.

10. The system according to claim 9 further comprising:

an attack-decay clock generator,

envelope information means, responsive to a signal indicating the opration of a key-actuated switch and to clock pulses from said attack-decay clock generator, for providing information regarding attack and decay envelopes, and

waveform modification means, cooprating with said envelope information means and said address composer means, for modifying said digitally composed waveshape in accordance with said information regarding attack and decay envelopes.

11. A system for generating tone source waveshapes comprising:

means for generating key identification signals in digital representation corresponding respectively to note-related fundamental frequencies of said waveshapes;

a keyboard switch circuit having a key-actuated switch for each of said notes for actuating said generating means to generate the key identification signal corresponding thereto;

an address generator responsive to the key identification signal for producing a given number of successive address signals periodically, each address signal consisting of a plurality of bits;

an address composer, connected to receive said successive address signals from said address generator and responsive to a predetermined number of said plurality of bits of each address signal in the range from one bit to n bits where n is more than one and not more than the bit plurality, for digitally composing a tone waveshape solely by carrying out arithmetic and/or logical operations directly on said predetermined number of address signal bits, said tone waveshape having a fundamental frequency corresponding to said generated key identification signal with an amplitude versus time characteristic determined by the digital word value of each predetermined number of address signal bits to which said address composer responds; and

means for converting the digitally composed tone waveshape into an analog equivalent thereof.

12. The system according to claim 11 which further comprises an attack-decay oscillator, an attack-decay logic circuit responsive to a signal indicating the operation of said key-actuated switch and the output from said attack-decay oscillator for producing an address signal, an attack-decay memory device storing information regarding attack and decay envelopes and connected to receive the address signal from the attack-decay logic circuit for producing said attack and decay envelope information, and a multiplier connected between said address composer and said digital-analog converting means for multiplying said digital tone signal by said attack and decay envelope information.

13. An electronic musical instrument comprising:

means for producing a set of digital addresses which progress through a fixed range of values in a certain time interval corresponding to the period of a selected musical note, and

digital logic circuitry means for forming waveform sample point amplitude values, without the use of a waveform memory, by manipulation of the digital address values themselves, said manipulation being carried out in unison with the progressive changes in digital address value so that the resultantly formed musical waveform has the period of said selected note.

14. An electronic musical instrument according to claim 13 further comprising:

a keyboard, said selected musical note being selected by actuation of a key,

an attack-decay clock generator,

envelope information means, responsive to said key actuation and to clock pulses from said generator, for providing information regarding attack and decay envelopes, and

waveform modification means, cooperating with said envelope information means and said digital logic circuitry means, for modifying said manipulation in accordance with said information regarding attack and decay envelopes.

15. An electronic musical instrument according to claim 13 wherein said manipulation consists of logical manipulation.

16. An electronic musical instrument according to claim 13 wherein said manipulation consists of arithmetic manipulation.

17. An electronic musical instrument according to claim 13 wherein said manipulation consists of combined logical and arithmetic manipulation.