Decoding of multichannel audio encoded bit streams using adaptive hybrid transformation

摘要

The processing efficiency of a process used to decode frames of an enhanced AC-3 bit stream is improved by processing each audio block in a frame only once. Audio blocks of encoded data are decoded in block order rather than in channel order. Exemplary decoding processes for enhanced bit stream coding features such as adaptive hybrid transform processing and spectral extension are disclosed.

主权项

1. A method for decoding a frame of an encoded digital audio signal, wherein:
the frame comprises frame metadata, a first audio block and one or more subsequent audio blocks; and each of the first and subsequent audio blocks comprises block metadata and encoded audio data for two or more audio channels, wherein:
the encoded audio data comprises scale factors and scaled values representing spectral content of the two or more audio channels, each scaled value being associated with a respective one of the scale factors; andthe block metadata comprises control information describing coding tools used by an encoding process that produced the encoded audio data, wherein the control information indicates that adaptive hybrid transform processing was used by the encoding process and wherein adaptive hybrid transform processing comprises:
applying an analysis filter bank implemented by a primary transform to the two or more audio channels to generate primary transform coefficients, andapplying a secondary transform to the primary transform coefficients for at least some of the two or more audio channels to generate hybrid transform coefficients;and wherein the method comprises:
(A) receiving the frame of the encoded digital audio signal; and (B) examining the encoded digital audio signal of the frame in a single pass to decode the encoded audio data for each audio block in order by block, wherein the decoding of each respective audio block comprises:
(1) if the respective audio block is the first audio block in the frame:
(a) obtaining all hybrid transform coefficients of a respective channel for the frame from the encoded audio data in the first audio block, and(b) applying an inverse secondary transform to the hybrid transform coefficients to obtain inverse secondary transform coefficients, and(2) obtaining primary transform coefficients from the inverse secondary transform coefficients for the respective channel in the respective audio block; and (C) applying an inverse primary transform to the primary transform coefficients to generate an output signal representing the respective channel in the respective audio block.