Data compression of sound data

• US 5,877,446 A
• Filed: 09/16/1997
• Issued: 03/02/1999
• Est. Priority Date: 01/18/1990
• Status: Expired due to Term

• Current Assignee: Creative Technology Ltd.
• Original Assignee: Creative Technology Ltd.
• Inventors: Murray, Donna L., Monahan, Kevin J.
• Primary Examiner(s): Witkowski, Stanley J.
• Application Number:
  US08/931,436
• Time in Patent Office: 532 Days
• Field of Search: 84/603-607, 84/619, 84/622-625, 84/627, 84/639-642, 84/657, 84/659-661, 84/663, 84/DIG. 9, 84/DIG. 10, 84/DIG. 26
• US Class Current: 84/603
• CPC Class Codes: G10H 1/125 using a digital filter
• CPC Class Codes: G10H 1/20 for transposition
• CPC Class Codes: G10H 2250/035 Crossfade, i.e. time domain amplitude envelope control of the transition between musical sounds or melodies, obtained for musical purposes, e.g. for ADSR tone generation, articulations, medley, remix audio mixers H04H60/04
• CPC Class Codes: G10H 2250/115 FIR impulse, e.g. for echoes or room acoustics, the shape of the impulse response is specified in particular according to delay times FIR filters for musical processing G10H2250/075
• CPC Class Codes: G10H 2250/481 Formant synthesis, i.e. simulating the human speech production mechanism by exciting formant resonators, e.g. mimicking vocal tract filtering as in LPC synthesis vocoders, wherein musical instruments may be used as excitation signal to the time-varying filter estimated from a singer's speech gensound singing voices G10H2250/455; parcor synthesis G10H2250/505; effect Helmholtz G10H2210/275
• CPC Class Codes: G10H 2250/571 Waveform compression, adapted for music synthesisers, sound banks or wavetables audio compression G10L19/00
• CPC Class Codes: G10H 7/008 Means for controlling the transition from one tone waveform to another
• CPC Class Codes: Y10S 84/10 Feedback

Abstract

A data compression method and apparatus for the compression of sound data utilized in digital sampling keyboard instruments. The present invention reduces memory requirements for sampled sounds without compromising sound quality, utilizing processing of sound data samples to delete sound data between the attack portion and just before the loop start portion. The improved method further includes a step of digitally splicing the remaining attack and loop portions to form a spliced data sample.

Claims

1. In a data compression method for the compression of sound data samples, the method comprising steps of:

splitting a sound data sample, having a fundamental frequency and a plurality of harmonic frequencies associated therewith, into a lowpass band, a bandpass band and a highpass band, such that the lowpass band includes the fundamental frequency of said data sample, the bandpass band includes the second harmonic frequency of said data sample, and the highpass band includes the remainder of the sound,

looping the lowpass band and the highpass band, using a single cycle loop and a double cycle loop to form a lowpass loop length and a highpass loop length, respectively, with said lowpass loop length defining a first looped band and said highpass loop length defining a second looped band,

looping the highpass band using a cross fade loop such that the longest loop length is an integer multiple of the other loop lengths, defining a third looped band, and

recombining the first, second and third looped bands into a recombined data sample.

2. The method as in claim 1 wherein the recombining step includes equalizing the loop lengths associated with said first, second and third looped bands.

3. The method as in claim 2 wherein the first, second and third looped bands starts occur at the same respective point.

4. In a data compression method for the compression of sound data sample, the method comprising steps of:

splitting a sound data sample, having a fundamental frequency, into at least a first band and a second band, such that said first band includes the fundamental frequency of said data sample, and the second band includes the remainder of the sound,

looping the first band using a single cycle loop to form a first loop length, defining a first loop band,

looping the second band using a cross fade loop such that the longest loop length is an integer multiple of the first loop length, defining a second loop band, and

recombining the first and second loop bands into a recombined data sample.

5. Data compression apparatus for compression of sound data samples, the apparatus comprising:

means for splitting a sound data sample, having a fundamental frequency and a plurality of harmonic frequencies, into a lowpass band, a bandpass band and a highpass band, such that the lowpass band includes the fundamental frequency of said data sample, the bandpass band includes the second harmonic of said data sample, and the highpass band includes the remainder of the sound,

first means, in data communication with said splitting means, for looping the lowpass band and highpass band, using a single cycle loop and a double cycle loop to form a lowpass and highpass loop length, respectively, with said lowpass loop length defining a first looped band and said highpass loop length defining a second looped band,

second means, in data communication with said first looping means, for looping the highpass band using a cross fade loop such that the longest loop length is an integer multiple of the other loop lengths, defining a third looped band, and

means, in data communication with both said first and second looping means, for recombining the first, second and third looped bands into a recombined data sample.

6. In a data compression method for compression of sound data, the method comprising steps of

sampling primary and secondary sound data samples at first and second sampling frequencies, respectively, each of said primary and said secondary sound data samples having an attack portion, an intermediate portion and a loop portion,

processing each of said primary and said secondary sound data samples having an attack portion and a cross-fade loop portion, including a step of deleting sound data between the attack portion and the loop portion,

digitally splicing the remaining attack and loop portions of each of said primary and said secondary sound data samples with a predetermined cross-fade time to form first and second spliced sound data samples, each of which has a fundamental frequency and a plurality of harmonic frequencies associated therewith,

splitting the first and second spliced sound data samples into a lowpass band, a bandpass band and a highpass band, such that the lowpass band includes the fundamental frequency of one of said first and second spliced sound data samples, the bandpass band includes the second harmonic of one of said first and second spliced sound data samples, and the highpass band includes the remainder of the sound,

looping the low pass and bandpass bands of each of said first and second spliced sound data samples using a single cycle loop for the lowpass band and a double cycle loop for the highpass band,

looping the highpass band of each of said first and second spliced sound data samples using a cross-fade loop such that the longest loop length of a given sample is an integer multiple of the other loop lengths that sample,

recombining the looped bands of each of said first and second spliced sound data samples into a first and a second recombined data samples,

pitch shifting one of said first and second recombined data samples to the remaining of said first and second recombined data samples to form a formant transposition thereof, defining transposed samples, and

digitally combining one of said primary and said secondary sound data samples with said transposed samples to form a combined sound data sample.

7. Data compression apparatus for the compression of sound data samples, the apparatus comprising:

means for sampling primary and secondary sound data samples at first and second sampling frequencies, respectively, each of said primary and secondary sound data samples having an attack portion, an intermediate portion and a loop portion,

means, in data communication with said sampling means for processing each of said primary and secondary sound data samples having an attack portion and a cross/faded loop portion, by deleting sound data between the attack portion and the loop portion,

means, in data communication with said processing means, for digitally splicing the remaining attack and loop portions of each of said primary and secondary sound data samples with a predetermined cross fade time to form first and second spliced sound data samples, each of which includes a fundamental frequency and a plurality of harmonic frequencies,

means, in data communication with said splitting means, for splitting each of said first and second spliced sound data samples into a lowpass band, a bandpass band and a highpass band, such that the lowpass band includes the fundamental frequency of one of said first and second spliced sound data samples, the bandpass band includes the second harmonic of said one of said first and second spliced sound data samples, and the highpass band includes the remainder of the sound,

means, in data communication with said splitting means, for looping the lowpass and bandpass bands of each of said first and second spliced sound data samples, using a single cycle loop for the lowpass band and a double cycle loop for the highpass band, forming first and second looped bands, respectively,

means, in data communication with both said looping means, for recombining the first and second looped bands into first and second recombined data samples,

means, in data communication with said recombining means, for pitch shifting one of said first and second recombined data samples to the remaining of said first and second recombined data samples to form a formant transposition thereof, detecting transposed samples and

means, in data communication with both said pitch shifting means and said sampling means, for digitally combining one of said primary and secondary sound data samples and transposed samples to form a combined sound data sample.