Abstract: An audio signal is conveyed more efficiently by transmitting or recording a baseband of the signal with an estimated spectral envelope and a noise-blending parameter derived from a measure of the signal's noise-like quality. The signal is reconstructed by translating spectral components of the baseband signal to frequencies outside the baseband, adjusting phase of the regenerated components to maintain phase coherency, adjusting spectral shape according to the estimated spectral envelope, and adding noise according to the noise-blending parameter. Preferably, the transmitted or recorded signal also includes an estimated temporal envelope that is used to adjust the temporal shape of the reconstructed signal.

Abstract: A receiver in an audio coding system receives a signal conveying frequency subband signals representing an audio signal. The subband signals are examined to assess one or more characteristics of the audio signal including temporal shape. Spectral components are synthesized having the one or more assessed characteristics, integrated with the subband signals and passed through a synthesis filterbank to generate an output signal.

Abstract: A receiver in an audio coding system receives a signal conveying frequency subband signals representing an audio signal. The subband signals are examined to assess one or more characteristics of the audio signal including temporal shape. Spectral components are synthesized having the one or more assessed characteristics, integrated with the subband signals and passed through a synthesis filterbank to generate an output signal.

Abstract: Audio coding processes like quantization can cause spectral components of an encoded audio signal to be set to zero, creating spectral holes in the signal. These spectral holes can degrade the perceived quality of audio signals that are reproduced by audio coding systems. An improved decoder avoids or reduces the degradation by filling the spectral holes with synthesized spectral components. An improved encoder may also be used to realize further improvements in the decoder.

Abstract: A method of modifying the operation of the encoder function and/or the decoder function of a perceptual coding system in accordance with supplemental information, such as a watermark, so that the supplemental information may be detectable in the output of the decoder function. One or more parameters are modulated in the encoder function and/or the decoder function in response to the supplemental information.

Abstract: A receiver in an audio coding system receives a signal conveying frequency subband signals representing an audio signal. The subband signals are examined to assess one or more characteristics of the audio signal. Spectral components are synthesized having the assessed characteristics. The synthesized spectral components are integrated with the subband signals and passed through a synthesis filterbank to generate an output signal. In one implementation, the assessed characteristic is temporal shape and noise-like spectral components are synthesized having the temporal shape of the audio signal.

Abstract: A receiver in an audio coding system receives a signal conveying frequency subband signals representing an audio signal. The subband signals are examined to assess one or more characteristics of the audio signal. Spectral components are synthesized having the assessed characteristics. The synthesized spectral components are integrated with the subband signals and passed through a synthesis filterbank to generate an output signal. In one implementation, the assessed characteristic is temporal shape and noise-like spectral components are synthesized having the temporal shape of the audio signal.

Abstract: In an audio coding system, an encoding transmitter represents encoded spectral components as normalized floating-point numbers. The transmitter provides first and second control parameters that may be used to transcode the encoded spectral parameters. A transcoder uses first control parameters to partially decode the encoded components and uses second control parameters to re-encode the components. The transmitter determines the second control parameters by analyzing the effects of arithmetic operations in the partial-decoding process to identify situations where the floating-point representations lose normalization. Exponents associated with the numbers that lose normalization are modified and the modified exponents are used to calculate the second control parameters.

Abstract: An audio encoder discards spectral components of an input signal and uses channel coupling to reduce the information capacity requirements of an encoded signal. Channel coupling represents selected spectral components of multiple channels of signals in a composite form. An audio decoder synthesizes spectral components to replace the discarded spectral components and generates spectral components for individual channel signals from the coupled-channel signal. The encoder provides scale factors in the encoded signal that improve the efficiency of the decoder to generate output signals that substantially preserve the spectral energy of the original input signals.

Abstract: The perceived quality of an audio signals obtained from very low bit-rate audio coding system is improved by using expanding quantizers and arithmetic coding in a transmitter and using complementary compression and arithmetic decoding in a receiver. An expanding quantizer is used to control the number of signal components that are quantized to zero and arithmetic coding is used to efficiently code the quantized-to-zero coefficients. This allows a wider bandwidth and more accurately quantized baseband signal to be conveyed to the receiver, which regenerates an output signal by synthesizing the missing components.

Abstract: An audio encoder discards spectral components of an input signal and uses channel coupling to reduce the information capacity requirements of an encoded signal. Channel coupling represents selected spectral components of multiple channels of signals in a composite form. An audio decoder synthesizes spectral components to replace the discarded spectral components and generates spectral components for individual channel signals from the coupled-channel signal. The encoder provides scale factors in the encoded signal that improve the efficiency of the decoder to generate output signals that substantially preserve the spectral energy of the original input signals.

Abstract: In an audio coding system, an encoding transmitter represents encoded spectral components as normalized floating-point numbers. The transmitter provides first and second control parameters that may be used to transcode the encoded spectral parameters. A transcoder uses first control parameters to partially decode the encoded components and uses second control parameters to re-encode the components. The transmitter determines the second control parameters by analyzing the effects of arithmetic operations in the partial-decoding process to identify situations where the floating-point representations lose normalization. Exponents associated with the numbers that lose normalization are modified and the modified exponents are used to calculate the second control parameters.

Abstract: An encoded bitstream assembled by an audio or video encoder is encrypted. The assembled encoded bitstream has a syntax. Data is selected in the assembled encoded bitstream, which data is less than all of the data in the bitstream and which, if encrypted, would result in a partly-encrypted bitstream that does not violate the syntax of the assembled encoded bitstream and would render reproduced audio or video resulting from an undecrypted decoding of the partly-encrypted bitstream to be of degraded quality. The selected data in the assembled encoded bitstream is encrypted to provide the partly encrypted bitstream.

Abstract: A method of modifying the operation of the encoder function and/or the decoder function of a perceptual coding system in accordance with supplemental information, such as a watermark, so that the supplemental information may be detectable in the output of the decoder function. One or more parameters are modulated in the encoder function and/or the decoder function in response to the supplemental in formation.

Abstract: The perceived quality of an audio signals obtained from very low bit-rate audio coding system is improved by using expanding quantizers and arithmetic coding in a transmitter and using complementary compression and arithmetic decoding in a receiver. An expanding quantizer is used to control the number of signal components that are quantized to zero and arithmetic coding is used to efficiently code the quantized-to-zero coefficients. This allows a wider bandwidth and more accurately quantized baseband signal to be conveyed to the receiver, which regenerates an output signal by synthesizing the missing components.

Abstract: A receiver in an audio coding system receives a signal conveying frequency subband signals representing an audio signal. The subband signals are examined to assess one or more characteristics of the audio signal. Spectral components are synthesized having the assessed characteristics. The synthesized spectral components are integrated with the subband signals and passed through a synthesis filterbank to generate an output signal. In one implementation, the assessed characteristic is temporal shape and noise-like spectral components are synthesized having the temporal shape of the audio signal.

Abstract: Audio coding processes like quantization can cause spectral components of an encoded audio signal to be set to zero, creating spectral holes in the signal. These spectral holes can degrade the perceived quality of audio signals that are reproduced by audio coding systems. An improved decoder avoids or reduces the degradation by filling the spectral holes with synthesized spectral components. An improved encoder may also be used to realize further improvements in the decoder.

Abstract: An audio signal is conveyed more efficiently by transmitting or recording a baseband of the signal with an estimated spectral envelope and a noise-blending parameter derived from a measure of the signal's noise-like quality. The signal is reconstructed by translating spectral components of the baseband signal to frequencies outside the baseband, adjusting phase of the regenerated components to maintain phase coherency, adjusting spectral shape according to the estimated spectral envelope, and adding noise according to the noise-blending parameter. Preferably, the transmitted or recorded signal also includes an estimated temporal envelope that is used to adjust the temporal shape of the reconstructed signal.

Abstract: Techniques like Huffman coding can be used to represent digital audio signal components more efficiently using non-uniform length symbols than can be represented by other coding techniques using uniform length symbols Unfortunately, the coding efficiency that can be achieved by Huffman coding depends on the probability density function of the information to be coded and the Huffman coding process itself requires considerable processing and memory resources. A coding process that uses gain-adaptive quantization according to the present invention can realize the advantage of using non-uniform length symbols while overcoming the shortcomings of Huffman coding. In gain-adaptive quantization, the magnitudes of signal components to be encoded are compared to one or more thresholds and placed into classes according to the results of the comparison. The magnitudes of the components placed into one of the classes are modified according to a gain factor that is related to the threshold used to classify the components.

Abstract: An audio encoder applies an adaptive block-encoding process to segments of audio information to generate frames of encoded information that are aligned with a reference signal conveying the alignment of a sequence of video information frames. The audio information is analyzed to determine various characteristics of the audio signal such as the occurrence and location of a transient, and a control signal is generated that causes the adaptive block-encoding process to encode segments of varying length. A complementary decoder applies an adaptive block-decoding process to recover the segments of audio information from the frames of encoded information. In embodiments that apply time-domain aliasing cancellation (TDAC) transforms, window functions and transforms are applied according to one of a plurality of segment patterns that define window functions and transform parameters for each segment in a sequence of segments.