Method and apparatus for producing an electronic representation of a musical sound using extended coerced harmonics

• US 5,466,882 A
• Filed: 01/11/1994
• Issued: 11/14/1995
• Est. Priority Date: 12/20/1990
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: Gulbransen, Inc. (Qrs Music Technologies, Inc.)
• Inventors: Lee, J. Robert
• Primary Examiner(s): Witkowski, Stanley J.
• Application Number:
  US08/179,923
• Time in Patent Office: 672 Days
• Field of Search: 84/601-608, 84/622-625, 84/627
• US Class Current: 84/603
• CPC Class Codes: G10H 2250/235 Fourier transform; Discrete Fourier Transform [DFT]; Fast Fourier Transform [FFT]
• CPC Class Codes: G10H 7/06 in which amplitudes are read at a fixed rate, the read-out address varying stepwise by a given value, e.g. according to pitch

Abstract

A technique for digitally processing a counterpart of a musical sound first transforms a set of time-domain samples of the sound into frequency-domain counterparts, gradually coerces the frequency-domain counterparts into integer multiples of a fundamental frequency of the sound, and then, in each of a plurality of amplitude transition portions, gradually changes the amplitudes of the frequency-domain counterparts from the beginning to the end of each amplitude transition portion.

Claims

1. A method of creating and preserving a counterpart of a sound having a fundamental frequency, the method utilizing a memory device and comprising the steps of:

generating a sequence of original time domain samples of the sound, the sequence including successive adjacent portions in which a first portion exhibits aperiodic fluctuations of amplitude of the sound, a second portion, following the first portion, exhibits decreasing aperiodic fluctuations of amplitude of sound, and a third portion, following the second portion, exhibits substantially periodic fluctuations of amplitude of the sound;

transforming the sequence of original time domain samples to frequency domain values including a set of frequency values representing component frequencies of the sound, the frequency domain values including the fundamental frequency and a plurality of related frequencies;

from the beginning of the second portion, changing the related frequencies in the set of frequency values such that the related frequencies are substantially integral multiples of the fundamental frequency by the end of the second portion;

from the beginning of a first loop portion, maintaining the related frequencies in the set of frequency values as substantially integral multiples of the fundamental frequency for a time substantially corresponding to one period of the fundamental frequency;

from the beginning of a fourth portion following the first loop portion, changing amplitudes of the related frequencies in the set of frequency values;

from an end of the fourth portion, maintaining the amplitudes and frequencies of the related frequencies in the set of frequencies for a time substantially corresponding to one period of the fundamental frequency; and

transforming the frequency domain values to a sequence of adjusted time domain values and storing the sequence of adjusted time domain values in the memory device.

2. A method for synthesizing sound made by a musical instrument, comprising the steps of:

generating a plurality of amplitude samples of the sound;

partitioning the plurality of amplitude samples into successive adjacent attack, frequency transition, first loop, amplitude transition, and second loop portions, wherein;

in the attack portion, the amplitude samples display aperiodic fluctuations in the amplitude of the sound;

in the frequency transition portion, the amplitude samples display decreasing aperiodic fluctuations of the amplitude of the sound;

in the first loop portion, amplitude transition portion, and second loop portion, the amplitude samples display substantially periodic fluctuation of the amplitude of the sound;

transforming the amplitude samples of the frequency transition portion into frequency and amplitude components of the sound, the frequency components including a fundamental frequency component and a plurality of related frequency components;

from the end of the attack portion until the beginning of the first loop portion, substantially continuously adjusting the value of each of said related frequency components over the length of the

frequency transition portion such that each of said related frequency components has substantially an integer ratio to the fundamental frequency by the beginning of the first loop portion;

from the beginning of the first loop portion until the end of the first loop portion, maintaining the frequency and amplitude of each of said related frequency components over the length of the first loop portion, the length of the first loop portion corresponding essentially to one period of the fundamental frequency;

from the beginning of the amplitude transition portion until the beginning of the second loop portion, substantially continuously adjusting the amplitude of each of said related frequency components over the length of the amplitude transition portion;

from the beginning of the second loop portion until the end of the second loop portion, maintaining the frequency and amplitude of each of said related frequency components, the length of the second loop portion corresponding substantially to a period of the fundamental frequency; and

transforming the frequency and amplitude components of the attack, first transition, first loop, second transition, and second loop portions back to amplitude values.

3. The method of claim 2, further including, for each loop portion, generating frequency and amplitude components of the sound for at least one period of the fundamental frequency, the frequency components including the fundamental frequency and the related frequency components, each of the related frequency components having substantially an integer ratio to the fundamental frequency, the frequency components of the first and second loop portions having phase continuity with the frequency components of the first and second transition portions, respectively.

4. In an apparatus for synthesizing musical notes in response to selection of keys on a keyboard, a combination comprising:

key conversion means for generating a sequence of address signals which corresponds to a selected key;

storage means connected to the key conversion means and containing stored amplitude signals at addressable storage locations for providing a sequence of amplitude signals representing a musical note corresponding to the selected key in response to the sequence of address signals, wherein;

the sequence of amplitude signals representing the amplitude of the musical note and including an attack portion in which the amplitude of the musical note exhibits aperiodic fluctuations, a first transition portion wherein the amplitude of the musical note exhibits decreasing aperiodic fluctuations, a first loop portion in which the amplitude of the musical note exhibits substantially periodic fluctuations, a second transition portion and a second loop portion;

the sequence of amplitude signals including a set of frequency components with a fundamental frequency and a plurality of related frequencies wherein the related frequencies in the first transition portion of the sequence of amplitude signals interpolate from first values to integral multiples of the fundamental frequency; and

,

wherein the amplitudes of the related frequencies in the second transition portion of the sequence of amplitude signals interpolate from first amplitude values to second amplitude values without changing the frequency values; and

output means connected to the storage means for producing an analog counterpart of the musical note in response to the sequence of amplitude signals.

5. An apparatus for transforming musical signals, comprising:

conversion means for converting a musical sound into a sequence of amplitude samples representing change in amplitude of musical sounds over time;

transform means connected to the conversion means for transforming successive, adjacent portions of the sequence of amplitude samples into frequency and amplitude components of musical sound, frequency components including a fundamental frequency in a plurality of related frequencies, the successive, adjacent portions including an attack portion in which the amplitude of the musical sound has aperiodic variations, a first transition portion following the attack portion in which the amplitude of the musical note has decreasing aperiodic variations, a first loop portion following the first transition portion, a plurality of bursts following the first loop portion, each burst including an amplitude transition portion followed by a loop portion;

first means in the transform means for substantially continuously adjusting the value of each of the related frequency components over the amplitude transition portion such that each of the related frequency components is a respective integer multiple of the fundamental frequency;

second means in the transform means for substantially continuously adjusting the value of the amplitude of each of the related frequency components over an amplitude transition portion;

conversion means for converting the frequency and amplitude

components back to a sequence of amplitude samples; and

means connected to the conversion means for storing a plurality of sequences of amplitude samples, each sequence of amplitude samples corresponding to a respective musical sound.

6. The apparatus of claim 5, wherein the transform means further includes means for maintaining the frequency and amplitude of each of said related frequency components over the length of each loop portion, the length of each loop portion corresponding substantially to one period of the fundamental frequency.

7. The apparatus of claim 5, wherein the transform means further includes means for preserving phase continuity between the frequency components of the attack portion and the frequency components of the transition portion.

8. The apparatus of claim 5, wherein each frequency of the related frequencies has a value at the end of the attack portion, and wherein the first means is further for interpolating values for each related frequency between a value for the related frequency at the end of the attack portion and an integer multiple of the fundamental frequency at the end of the frequency transition portion.

9. The apparatus of claim 5, wherein each frequency of the related frequencies has, for each amplitude transition portion, a value at the beginning of the amplitude transition portion and a value at the end of the amplitude transition portion and wherein the second means is further for interpolating amplitude values for each related frequency between the amplitude value for the related frequency at the beginning of the amplitude transition portion and the amplitude value for the related frequency at the end of the amplitude transition portion.