Scalable audio coder and decoder
First Claim
1. A method for processing a signal, said method comprising:
- receiving an input audio signal in digital format;
computing a modulated lapped transform with first analysis and synthesis windows from the received input audio signal;
modifying the modulated lapped transform to produce a nonuniform modulated lapped transform having high-frequency subbands and second analysis and synthesis windows different from the first analysis and synthesis windows;
combining the high-frequency subbands to enhance time resolution; and
switching the combined high-frequency subbands based on predetermined signal spectrum information for efficiently processing the audio signal.
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Abstract
The coder/decoder (codec) system of the present invention includes a coder and a decoder. The coder includes a multi-resolution transform processor, such as a modulated lapped transform (MLT) transform processor, a weighting processor, a uniform quantizer, a masking threshold spectrum processor, an entropy encoder, and a communication device, such as a multiplexor (MUX) for multiplexing (combining) signals received from the above components for transmission over a single medium. The decoder comprises inverse components of the encoder, such as an inverse multi-resolution transform processor, an inverse weighting processor, an inverse uniform quantizer, an inverse masking threshold spectrum processor, an inverse entropy encoder, and an inverse MUX. With these components, the present invention is capable of performing resolution switching, spectral weighting, digital encoding, and parametric modeling.
265 Citations
20 Claims
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1. A method for processing a signal, said method comprising:
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receiving an input audio signal in digital format; computing a modulated lapped transform with first analysis and synthesis windows from the received input audio signal; modifying the modulated lapped transform to produce a nonuniform modulated lapped transform having high-frequency subbands and second analysis and synthesis windows different from the first analysis and synthesis windows; combining the high-frequency subbands to enhance time resolution; and switching the combined high-frequency subbands based on predetermined signal spectrum information for efficiently processing the audio signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A coder stored on computer readable memory of a computer system for coding an input audio signal, the coder comprising:
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a multi-resolution transform processor for receiving the input audio signal in a digital format and producing transform coefficients from the input audio signal; a weighting processor with a masking threshold spectrum processor for masking quantization noise by spectrally weighting and partial whitening the transform coefficients; a uniform quantizer for converting continuous values to discrete values; an entropy encoder for encoding the transform coefficients; and a parametric modeling processor for producing a dictionary of input strings from symbol probabilities, wherein the input strings are used by the entropy encoder for efficiently coding the audio signal. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. A digital audio coder comprising:
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a multi-resolution modulated lapped transform module residing in computer readable memory and preprogrammed to receive an input audio signal and transform the input audio signal into a modulated lapped transform having first analysis and synthesis windows; a modifier preprogrammed to modify the modulated lapped transform for producing a nonuniform modulated lapped transform having high-frequency subbands and second analysis and synthesis windows different from the first analysis and synthesis windows; and a combiner preprogrammed to combine the high-frequency subbands for enhancing time resolution and for switching the combined high-frequency subbands based on predetermined signal spectrum information for efficiently coding the audio signal. - View Dependent Claims (18, 19, 20)
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Specification