Audio coding systems and methods
First Claim
Patent Images
1. An audio coding system for encoding and decoding an audio signal, said system including an encoder and a decoder, said encoder comprising:
- means for decomposing said audio signal into an upper and a lower sub-band signal;
lower sub-band coding means for encoding said lower sub-band signal;
upper sub-band coding means for encoding at least the non-periodic component of said upper sub-band signal according to a source-filter model;
said decoder means comprising means for decoding said encoded lower sub-band signal and said encoded upper sub-band signal, and for reconstructing therefrom an audio output signal, wherein said decoding means comprises filter means and excitation means for generating an excitation signal for being passed by said filter means to produce a synthesised audio signal, said excitation means being operable to generate an excitation signal which includes a substantial component of synthesised noise in an upper frequency band corresponding to the upper sub-band of said audio signal.
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Abstract
An audio signal is decomposed into lower and upper sub-band and at least the noise component of the sub-band is encoded. At the decoder the audio signal is synthesised by a decoding means which utilises a synthesised noise excitation signal and a filter to reproduce the noise component in the upper sub-band.
144 Citations
36 Claims
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1. An audio coding system for encoding and decoding an audio signal, said system including an encoder and a decoder, said encoder comprising:
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means for decomposing said audio signal into an upper and a lower sub-band signal;
lower sub-band coding means for encoding said lower sub-band signal;
upper sub-band coding means for encoding at least the non-periodic component of said upper sub-band signal according to a source-filter model;
said decoder means comprising means for decoding said encoded lower sub-band signal and said encoded upper sub-band signal, and for reconstructing therefrom an audio output signal, wherein said decoding means comprises filter means and excitation means for generating an excitation signal for being passed by said filter means to produce a synthesised audio signal, said excitation means being operable to generate an excitation signal which includes a substantial component of synthesised noise in an upper frequency band corresponding to the upper sub-band of said audio signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 31, 32, 33, 34, 35)
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18. An audio coding method for encoding and decoding an audio signal, which method comprises:
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decomposing said audio signal into an upper and a lower sub-band signal;
encoding said lower sub-band signal;
encoding at least the non-periodic component of said upper sub-band signal according to a source-filter model, and decoding said encoded lower sub-band signal and said encoded upper sub-band signal to reconstruct an audio output signal;
wherein said decoding step includes providing an excitation signal which includes a substantial component of synthesised noise in an upper frequency bandwidth corresponding to the upper sub-band of said audio signal, and passing said excitation signal through a filter means to produce a synthesised audio signal.
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19. An audio decoder for decoding an audio signal encoded by decomposing said audio signal into an upper and a lower sub-band signal, encoding said lower sub-band signal and encoding at least a noise component of said upper sub-band signal according to a source-filter model, said decoder comprising:
filter means and excitation means for generating an excitation signal for being passed by said filter means to produce a synthesised audio signal, said excitation means being operable to generate an excitation signal which includes a substantial component of synthesised noise in an upper frequency band corresponding to the upper sub-bands of said audio signal.
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20. A method of decoding an audio signal encoded by decomposing said audio signal into an upper and a lower sub-band signal, encoding said lower sub-band signal and encoding at least a noise component of said upper sub-band signal according to a source-filter model, said method comprising:
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providing an excitation signal which includes a substantial component of synthesised noise in an upper frequency bandwidth corresponding to the upper sub-band of the input audio signal, and passing said excitation signal through a filter means to produce a synthesised audio signal.
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21. A coder system for encoding and decoding a speech signal, said system comprising encoder means and decoder means, said encoder means including:
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filter means for decomposing said speech signal into lower and upper sub-bands together defining a bandwidth of at least 5.5 kHz;
lower sub-band vocoder analysis means for performing a relatively high order vocoder analysis on said lower sub-band to obtain vocoder coefficients including LPC coefficients representative of said lower sub-band;
upper sub-band vocoder analysis means for performing a relatively low order vocoder analysis on said upper sub-band to obtain vocoder coefficients including LPC coefficients representative of said upper sub-band;
coding means for coding vocoder parameters including said lower and upper sub-band coefficients to provide an encoded signal for storage and/or transmission, and said decoder means including;
decoding means for decoding said encoded signal to obtain vocoder parameters including said lower and upper sub-band vocoder coefficients;
synthesising means for constructing an LPC filter from the vocoder parameters from said upper and lower sub-bands and for synthesising said speech signal from said filter and from an excitation signal. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 36)
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29. A voice encoder apparatus for encoding a speech signal, said encoder apparatus including:
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filter means for decomposing said speech signal into lower and upper sub-bands;
low band vocoder analysis means for performing a relatively high order vocoder analysis on said lower sub-band signal to obtain vocoder coefficients representative of said lower sub-band;
upper band vocoder analysis means for performing a relatively low order vocoder analysis on said upper sub-band signal to obtain vocoder coefficients representative of said upper sub-band, and coding means for coding said low and high sub band vocoder coefficients to provide an encoded signal for storage and/or transmission. - View Dependent Claims (30)
decoding means for decoding said encoded signal to obtain LPC parameters including said lower and upper sub-band LPC coefficients, and synthesising means for constructing an LPC filter from the vocoder parameters for said upper and said lower sub-bands and for synthesising said speech signal from said filter and from an excitation signal.
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Specification