Method of synthesizing a musical sound

• US 4,018,121 A
• Filed: 05/02/1975
• Issued: 04/19/1977
• Est. Priority Date: 03/26/1974
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Chowning, John M.
• Primary Examiner(s): Witkowski, Stanley J.
• Application Number:
  US05/573,933
• Time in Patent Office: 718 Days
• Field of Search: 84/1.01, 84/1.24, 84/1.25
• US Class Current: 84/696
• CPC Class Codes: G10H 1/02 Means for controlling the tone frequencies, e.g. attack or decay; Means for producing special musical effects, e.g. vibratos or glissandos
• CPC Class Codes: G10H 1/06 Circuits for establishing the harmonic content of tones , or other arrangements for changing the tone colour
• CPC Class Codes: G10H 7/002 using a common processing for different operations or calculations, and a set of microinstructions (programme) to control the sequence thereof

Abstract

Musical sounds are synthesized by means of frequency modulation with the carrier and modulating frequencies being in the audio range and the modulating index being related to a function to control the bandwidth and evolution in time of the partial frequencies of synthesized sound.

Claims

1. A method of synthesizing a musical sound composed of a plurality of component frequencies and characterized by a time-varying amplitude envelope having a time-varying attack portion, a substantially steady-state portion and a time-varying decay portion, the steps comprising,

generating a signal ω

_c to define a carrier frequency in the audio range,

generating a signal ω

_m to define a modulation frequency in the audio range,

generating a signal I(t) to define a time-varying modulation index,

frequency modulating ω

_c with ω

_m to form a frequency modulated wave defined by e = Asin [ω

_c t + I(t) sin ω

_m t] where e defines the instantaneous amplitude of said wave, A defines the peak amplitude of said wave, and [ω

_c t + I(t) sin ω

_m t] defines the frequency spectrum of said wave wherein the frequency spectrum of said wave changes as a function of the modulation index I(t) to form a representation of said sound.

2. A method as in claim 1 including the step of varying I(t) as a function of the attack portion of said amplitude envelope.

3. In a digital apparatus having storage means for storing signals including an audio-range carrier frequency signal ω

_c, including an audio-range modulation frequency signal ω

_m, including a time-varying modulation index signal I(t), and including an output amplitude signal A;

having waveform means for providing waveform signals as a function of input angles; and

having arithmetic means for arithmetically combining signals;

a method of synthesizing a musical sound comprising the steps of,

accessing from said storage means, periodically with time t, the signals ω

_m, ω

_c, I(t) and A,

transferring said signal ω

_m as an input angle to said waveform means to provide periodically a modulation waveform signal,

multiplying, in said arithmetic means, said modulation waveform signal and a value of said signal I(t) to form periodically a modulation component signal,

adding, in said arithmetic means, said modulation component signal and the signal ω

_c to obtain periodically an output angle signal,

transferring said output angle signal to said waveform means to obtain periodically an output waveform signal,

multiplying, in said arithmetic means, said output waveform signal by said signal A to provide an output signal to produce said musical sound.

4. An apparatus for electrically synthesizing musical sound comprising,

store means for storing signals proportional to amplitudes A of an output signal e, for storing signals proportional to audio-range carrier frequencies ω

_c, for storing signals proportional to modulation frequencies ω

_m, for storing signals proportional to amplitude modulation indexes I(t) where I(t) varies as a function of time t,

accessing means for accessing said signals, periodically with time t, from said store means,

processing means for processing said signals accessed from said store means to form said output signal equal to A sin [ω

_c t + I(t) sin ω

_m t],

audio transducer means responsive to said output signal for providing an audio signal output representing said musical sound.

5. An apparatus for synthesizing musical sound composed of a plurality of frequency components and characterized by a time-varying amplitude envelope including a time-varying attack portion, a substantially steady-state portion and a time-varying decay portion, said apparatus comprising,

sine wave means for producing signals proportional to the sine of input angles,

an adder,

a multiplier,

a temporary store,

frequency store means for storing values of audio-range frequency signals including carrier frequency signals ω

_c t and modulation frequency signals ω

_m t,

amplitude store means for storing amplitude signals including time-varying amplitude modulation signals I(t) and output amplitude signals A,

means for connecting periodically a modulation frequency signal ω

_m t as an input angle to said sine wave means to produce signal sin ω

_m t in said temporary store,

means for connecting periodically said signal sin ω

_m t to said multiplier and means for connecting periodically time-varying values of said signal I(t) to said multiplier to form periodically a product signal I(t) sin ω

_m t in said temporary store,

means for connecting periodically said signal I(t) sin ω

_m t to said adder means and means for connecting periodically a carrier frequency signal ω

_c t to said adder to form periodically a sum signal [ω

_c t + I(t) sin ω

_m t] in said temporary store,

means for connecting periodically said signal [ω

_c t + I(t) sin ω

_m t] as an input angle to said sine wave means whereby said sine wave means periodically provides a signal sin [ω

_c t + I(t) sin ω

_m t] in said temporary store,

means for connecting periodically said signal sin [ω

_c t + I(t) sin ω

_m t ] to said multiplier and means for connecting periodically an amplitude value A to said multiplier to provide periodically an output signal A sin [ω

_c t + I(t) sin ω

_m t] in said temporary store,

audio transducer means responsive to said output signal for providing an audio signal representing said musical sound.

6. The apparatus of claim 5, wherein said frequency store means includes means for storing said signals ω

_m t and ω

_c t such that ω

_c is an integral multiple of ω

_m whereby said output signal has a frequency spectrum including only odd harmonics.

7. The apparatus of claim 6 wherein said frequency store means includes means for storing said signals ω

_m t and ω

_c t such that the ratio ω

_c /ω

_m is equal to 2/1.

8. The apparatus of claim 5 wherein said amplitude store means includes means for storing said modulation index signal I(t) directly proportional to said attack portion of said amplitude envelope and said frequency store means includes means for storing the signals ω

_c t and ω

_m t such that the ratio ω

_c /ω

_m is equal to ω

_c /1 whereby the frequency spectrum of said output signal includes both odd and even harmonics for producing musical sound with the timbrel quality of brass instruments.

9. The apparatus of claim 8 where said means for storing the signals ω

_c t and ω

_m t stores values such that ω

_c /ω

_m is equal to 1/1.

10. The apparatus of claim 5 in which said frequency store means includes means for storing ω

_c t and ω

_m t such that the ratio of ω

_c /ω

_m is equal to an irrational number whereby the frequency spectrum of said output signal includes inharmonic frequencies.

11. The apparatus of claim 5 wherein said frequency store means includes means for storing the frequency signals ω

_c t equal to ω

_c1 t + ω

_c2 t where ω

_c1 and ω

_c2 are unequal frequencies.

12. The apparatus of claim 11 where said frequency store means store ω

_c1 t, ω

_c2 t and ω

_m such that the ratio ω

_c2 /ω

_m is equal to 7/1 and such that the ratio ω

_c1 /ω

_m is equal to 1/1.

13. The apparatus of claim 5 wherein said frequency store means includes means for storing said frequency signals ω

_m t as first frequency signals ω

_m1 t and second frequency signals ω

_m2 t, wherein said amplitude store means includes means for storing said modulation signals I(t) as first amplitude modulation signals I₁ (t) and as second amplitude modulation signals I₂ (t), whereby said output signal is Asin [ω

_c t + I₁ (t) sin ω

_m1 t + I₂ (t) sin ω

_m2 t].

14. The apparatus of claim 5 wherein said amplitude store means includes means for storing said output amplitude signals A as a function of said time-varying amplitude envelope.