Computationally efficient adaptive bit allocation for encoding method and apparatus with allowance for decoder spectral distortions
First Claim
1. An encoding method for constructing an encoded representation of an input signal for decoding by a decoding method that comprises applying a plurality of synthesis filters, said encoding method comprisinggenerating subband signals by applying a plurality of analysis filters to said input signal;
- producing, in response to said subband signals, encoded information having lower informational requirements than said subband signals, wherein said lower information requirements are achieved using a masking threshold established according to psycho-perceptual principles and by allowing for spectral distortions introduced by said decoding method, said allowing for spectral distortions being responsive to rate of rolloff of said masking threshold and rate of rolloff of frequency response of said plurality of synthesis filters; and
assembling said encoded information into said encoded representation.
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Abstract
The invention relates in general to low bit-rate encoding and decoding of information such as audio information. More particularly, the invention relates to computationally efficient adaptive bit allocation and quantization of encoded information useful in high-quality low bit-rate coding systems.
In audio applications, a digital split-band encoder splits an input signal into frequency subband signals having bandwidths commensurate with the critical bandwidths of the human auditory system, quantizes the subband signals according to values established by an allocation function, and assembles the quantized subband signals into an encoded signal. The allocation function establishes allocation values in accordance with psychoacoustic principles with allowance for decoding synthesis filter bank spectral distortions.
In one embodiment, an allocation function establishes allocation values using a psychoacoustic masking threshold generated by estimating the power spectral density (PSD) of the input signal, generating an excitation pattern by applying a basilar-membrane spreading function to the PSD, adjusting the excitation pattern by an amount equal to a sensitivity function which specifies a signal-to-noise ratio (SNR) sufficient to achieve psychoacoustic masking, comparing the level of the adjusted pattern to the threshold of hearing and generating the psychoacoustic masking threshold which is equal to the larger of the two. An allocation function may allow for decoder synthesis filter bank spectral distortions in any of a number of ways such as by adapting the sensitivity function.
132 Citations
24 Claims
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1. An encoding method for constructing an encoded representation of an input signal for decoding by a decoding method that comprises applying a plurality of synthesis filters, said encoding method comprising
generating subband signals by applying a plurality of analysis filters to said input signal; -
producing, in response to said subband signals, encoded information having lower informational requirements than said subband signals, wherein said lower information requirements are achieved using a masking threshold established according to psycho-perceptual principles and by allowing for spectral distortions introduced by said decoding method, said allowing for spectral distortions being responsive to rate of rolloff of said masking threshold and rate of rolloff of frequency response of said plurality of synthesis filters; and assembling said encoded information into said encoded representation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for constructing an encoded representation of an input signal for decoding by a decoder that comprises applying a plurality of synthesis filters, said apparatus comprising
means for generating subband signals by applying a plurality of analysis filters to said input signal; -
means for producing, in response to said subband signals, encoded information having lower informational requirements than said subband signals, said means for producing encoded information comprising means for achieving said lower information requirements using a masking threshold established according to psycho-perceptual principles; and means, responsive to rate of rolloff of said masking threshold and rate of rolloff of frequency response of said plurality of synthesis filters, for allowing for spectral distortions introduced by said decoder; and means for assembling said encoded information into said encoded representation. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
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19. An apparatus for decoding an encoded representation of an input signal, said decoder comprising
means for extracting quantized subband information from said encoded representation; -
allocation means for establishing allocation values by using a masking threshold established according to psycho-perceptual principles and by allowing for spectral distortions introduced by a plurality of synthesis filters, said allowing for spectral distortions being responsive to rate of rolloff of said masking threshold and rate of rolloff of frequency response of said plurality of synthesis filters; means for generating dequantized subband information by dequantizing said quantized subband information in accordance with said allocation values; and means for generating an output signal by applying said plurality of synthesis filters to said dequantized subband information. - View Dependent Claims (20, 21, 22, 23, 24)
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Specification