US 6,205,430 B1Granted

Audio decoder with an adaptive frequency domain downmixer

AssigneeSTMicroelectronics Asia Pacific Pte Ltd

InventorYau Wai Lucas Hui

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Abstract

A method and apparatus for decoding a multi-channel audio bitstream in which adaptive frequency domain downmixer (3) is used to downmix, according to long and shorter transform block length information (17), the decoded frequency coefficients of the multi-channel audio (12,13,14,15) such that the long and shorter transform block information is maintained separately within the mixed down left and right channels. In this way, the long and shorter transform block coefficients of the mixed down let and right channels can be inverse transformed adaptively (4,5,6,7) according to the long and shorter transform block information, and the results of the inverse transform of the long and short block of each the left and right channel added together (8,9) to form the total mixed down output of the left and right channel.

Claims6

Dependent claims

A method of decoding a multi-channel audio bitstream comprising the steps of subjecting said multi-channel audio bitstream to a block decoding process to obtain frequency coefficients for each audio channel within each block in the said multi-channel audio bitstream, unpacking long and shorter transform block information for each audio channel within said block from said multi-channel audio bitstream, and determining downmixing coefficients for each audio channel within said multi-channel audio bitstream, the method including the steps of:

(a) downmixing said frequency coefficients of each audio channel within said block which are identified as long transform block by said long and shorter transform block information to form a left mixed down for long transform block and a right mixed down for long transform block;
(b) downmixing said frequency coefficients of each audio channels within the said block which are identified as shorter transform block by said long and shorter transform block information to form a left mixed down for shorter transform block and a right mixed down for shorter transform block;
(c) inverse transforming each of said left mixed down for long transform block, said right mixed down for long transform block, said left mixed down for shorter transform block, and said right mixed down for shorter transform block to produce a left mixed down long inverse transformed block, a right mixed down long inverse transformed block, a left mixed down shorter inverse transformed block, and a right mixed down shorter inverse transformed block respectively;
(d) adding said left mixed down long inverse transformed block and said left mixed down shorter inverse transformed block to form a left total mixed down;
and
(e) adding said right mixed down long inverse transformed block and said right mixed down shorter inverse transformed block to form a right total mixed down.

3 more elements

An apparatus for decoding a multi-channel audio bitstream comprising means for block decoding said multi-channel audio bitstream to obtain frequency coefficients of each audio channel with each block, means for unpacking long and shorter transform block information for each audio channel within said block, and means for determining downmixing coefficients for each audio channel within said multi-channel audio bitstream, the apparatus including:

(a) means for downmixing said frequency coefficients of each audio channel identified as long transform block by said long and shorter transform block information to form a left mixed down for long transform block and a right mixed down for long transform block;
(b) means for downmixing said frequency coefficients of each audio channel identified as shorter transform block by said long and shorter transform block information to form a left mixed down for shorter transform block and a right mixed down for shorter transform block;
(c) means for inverse transforming each of said left mixed down for long transform block, said right mixed down for long transform block, said left mixed down for shorter transform block, and said right mixed down for shorter transform block to produce a left mixed down long inverse transformed block, a right mixed down long inverse transformed block, a left mixed down shorter inverse transformed block, and a right mixed down shorter inverse transformed block respectively;
(d) means for adding said left mixed down long inverse transformed block and said left mixed down shorter inverse transformed block to form a left total mixed down;
(e) means for adding of said right mixed down long inverse transformed block and said right mixed down shorter inverse transformed block to form a right total mixed down.

2 more elements

Dependencies are inferred from the claim text.