Method and apparatus for wavelet based data compression having adaptive bit rate control for compression of audio information
First Claim
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1. A method for compressing digitally sampled audio data comprising the steps of:
- a) determining a desired average bit rate;
b) performing a discrete wavelet transform on the digitally sampled data to obtain the resultant wavelet coefficients in such a manner that the resultant wavelet coefficients fall into critical bands that approximate a psychoacoustic model;
c) calculating a control parameter related to the fractional percentage of wavelet coefficients which must be eliminated to achieve the desired average bit rate;
d) using said control parameter to eliminate wavelet coefficients according to a predetermined criteria;
e) quantizing the wavelet coefficients using a selected quantization level;
f) entropy encoding the quantized coefficients; and
g) feeding the number of bits used to represent the entropy encoded coefficients back into the calculation of the control parameter used to eliminate wavelet coefficients so that the desired average bit rate is achieved.
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Abstract
The compression method utilizes a combination of both lossy and lossless compression to achieve significant compression while retaining very high subjective quality of the reconstructed or decompressed signal. Methods and apparatus for compression and decompression of digital audio data are provided. In one preferred embodiment, the compression method or apparatus employs an approximation of a psychoacoustic model for wavelet packet decomposition and has a bit rate control feedback loop particularly well suited to matching the output bit rate of the data compressor to the bandwidth capacity of a communication channel.
202 Citations
65 Claims
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1. A method for compressing digitally sampled audio data comprising the steps of:
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a) determining a desired average bit rate; b) performing a discrete wavelet transform on the digitally sampled data to obtain the resultant wavelet coefficients in such a manner that the resultant wavelet coefficients fall into critical bands that approximate a psychoacoustic model; c) calculating a control parameter related to the fractional percentage of wavelet coefficients which must be eliminated to achieve the desired average bit rate; d) using said control parameter to eliminate wavelet coefficients according to a predetermined criteria; e) quantizing the wavelet coefficients using a selected quantization level; f) entropy encoding the quantized coefficients; and g) feeding the number of bits used to represent the entropy encoded coefficients back into the calculation of the control parameter used to eliminate wavelet coefficients so that the desired average bit rate is achieved. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for compressing digitally sampled audio data which has been divided into data frames containing a predefined number of digital audio data samples, the method comprising the steps of:
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a) performing a discrete wavelet transform on the data frame to obtain the corresponding wavelet coefficients; b) decomposing the resultant wavelet coefficients into critical bands that approximate a psychoacoustic model; c) calculating a control parameter used to eliminate wavelet coefficients in this frame in order to achieve a desired average bit rate; d) selecting a quantization level for the wavelet coefficients based on a psychoacoustic model which uses one or more parameters derived from the data in the data frame; e) quantizing the wavelet coefficients at the selected quantization level; f) entropy encoding the quantized wavelet coefficients; and g) feeding the number of bits used to represent the entropy encoded coefficients back into the calculation of the control parameter so that the desired average bit rate is achieved. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A method of reconstructing digitally sampled audio information which has been previously compressed, the method comprising the steps of:
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a) entropy decoding the compressed digitally sampled audio information; b) decomposing the compressed digitally sampled audio information into critical bands that approximate a psychoacoustic model; c) performing an inverse discrete wavelet transform; and d) resealing the transformed data into the time domain. - View Dependent Claims (29, 30, 31)
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32. An article of manufacture comprising:
a) a computer usable medium having computer readable program code means embedded therein for compressing digitally sampled audio data, the computer readable program code means comprising; i) means for determining a desired average bit rate; ii) means for performing a discrete wavelet transform on the digitally sampled data to obtain the resultant wavelet coefficients in such a manner that the resultant wavelet coefficients fall into critical bands that approximate a psychoacoustic model; iii) means for calculating a control parameter used to eliminate symbols representing wavelet coefficients in order to achieve the desired average bit rate; iv) means for eliminating a plurality of wavelet coefficients according to a predetermined criteria; v) means for quantizing the wavelet coefficients using a selected quantization level; vi) means for entropy encoding the quantized coefficients; and vii) means for feeding the number of bits used to represent the entropy encoded coefficients back into the calculation of the control parameter in order to achieve the desired average bit rate. - View Dependent Claims (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46)
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47. An article of manufacture comprising:
a) a computer usable medium having computer readable program code means embedded therein for compressing digitally sampled data, the computer readable program code means comprising; i) means for dividing the data into data frames containing a predefined number of digital data samples; ii) means for performing a discrete wavelet transform on the data frame to obtain the corresponding wavelet coefficients in such a manner that the wavelet coefficients fall into critical bands that approximate a psychoacoustic model; iii) means for calculating a control parameter used to adjust the instantaneous bit rate in order to achieve a desired average bit rate; iv) means for eliminating a plurality of wavelet coefficients according to a predefined criteria; v) means for selecting a quantization level for the wavelet coefficients based on the psychoacoustic model which uses one or more parameters derived from the data in the data frame; vi) means for quantizing the wavelet coefficients at the selected quantization level; vii) means for entropy encoding the quantized wavelet coefficients; and viii) means for feeding the number of bits used to represent the entropy encoded coefficients back into the calculation of the control parameter in order to achieve the desired average bit rate. - View Dependent Claims (48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58)
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59. An article of manufacture comprising:
a) a computer usable medium having computer readable code means embedded therein for reconstructing digitally sampled information which has been previously compressed, the computer readable code means comprising; i) means for entropy decoding the compressed digitally sampled audio information to obtain entropy decoded information comprising wavelet coefficients; ii) means for decomposing the compressed digitally sampled audio information into critical bands that approximate a psychoacoustic model; iii) means for performing an inverse discrete wavelet transform on the entropy decoded information contained within the critical bands to obtain inverse wavelet transformed data; and iv) means for resealing the inverse wavelet transformed data into the time domain. - View Dependent Claims (60, 61)
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62. A method for compressing digitally sampled audio data comprising the steps of:
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determining a desired average bit rate; performing a discrete wavelet transform on the digitally sampled data to obtain resultant wavelet coefficients in a plurality of wavelet bands; selecting the number of bits that will be used to quantize the wavelet coefficients in said plurality of wavelet bands; encoding the wavelet coefficients in each of said plurality of wavelet bands with an entropy encoder to obtain a plurality of individually encoded wavelet bands; assembling the individually encoded wavelet bands into a single compressed output data frame; and feeding the number of bits used to represent the single compressed output data frame back into the selection of the number of bits used to quantize the wavelet coefficients in said plurality of wavelet bands.
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63. A method for compressing digitally sampled audio data comprising the steps of:
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performing a discrete wavelet transform on the digitally sampled data to obtain resultant wavelet coefficients in a plurality of wavelet bands; selecting the number of bits that will be used to quantize the wavelet coefficients in said plurality of wavelet bands; encoding the wavelet coefficients in each of said plurality of wavelet bands with an entropy encoder to obtain a plurality of individually encoded wavelet bands; and assembling the individually encoded wavelet bands into a single compressed output data frame.
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64. A computer-readable medium having computer-executable instructions comprising:
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means for performing a discrete wavelet transform on digitally sampled audio data to obtain the resultant wavelet coefficients in such a manner that the resultant wavelet coefficients fall into critical bands that approximate a psychoacoustic model of a human ear; means for quantizing said wavelet coefficients to a selected quantization level, said means for quantizing being adapted to quantize the wavelet coefficients in each of said critical bands to obtain a plurality of quantized critical bands; means for individually entropy encoding each of said plurality of quantized critical bands; and means for controlling the bit rate from said means for individually entropy encoding by controlling the selected quantization level based on the number of bits at the output of said means for individually entropy encoding.
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65. A computer-readable medium having computer-executable instructions comprising:
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means for performing a discrete wavelet transform on digitally sampled audio data to obtain the resultant wavelet coefficients in such a manner that the resultant wavelet coefficients fall into critical bands that approximate a psychoacoustic model of a human ear; means for quantizing said wavelet coefficients to a selected quantization level, said means for quantizing being adapted to quantize the wavelet coefficients in each of said critical bands to obtain a plurality of quantized critical bands; and means for individually entropy encoding each of said plurality of quantized critical bands.
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Specification