Audio decoder with an adaptive frequency domain downmixer

• US 6,205,430 B1
• Filed: 06/21/1999
• Issued: 03/20/2001
• Est. Priority Date: 10/24/1996
• Status: Expired due to Term

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: Hui, Yau Wai Lucas
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Azad, Abul K.
• Application Number:
  US09/297,112
• Time in Patent Office: 638 Days
• Field of Search: 704/500, 704/501, 704/502, 704/503, 704/504
• US Class Current: 704/500
• CPC Class Codes: H04H 20/88 Stereophonic broadcast systems multiplex system in general H04J

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.

Claims

1. 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.

2. A method according to claim 1, wherein said block decoding process comprises the steps of:

(a) parsing the said multi-channel audio bitstream to obtain bit allocation information on each audio channel within said block;

(b) unpacking quantized frequency coefficients from said block using said bit allocation information; and

(c) de-quantizing said quantized frequency coefficients to obtain said frequency coefficients using said bit allocation information.

3. A method according to claim 2, further including a post-processing step comprising:

(a) subjecting said left total mixed down to a window overlap/add process wherein the samples within said left total mixed down are weighted, de-interleaved, overlapped and added to samples of a previous block;

(b) subjecting said right total mixed down to a window overlap/add process wherein the samples within said right total mixed down are weighted, de-interleaved, overlapped and added to samples of a previous block; and

(c) subjecting the results of the window overlap/add to an output process wherein said results of the window overlay/add process are formatted and outputted.

4. 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.

5. An apparatus according to claim 4, wherein said means for block decoding comprises:

(a) means for parsing said multi-channel audio bitstream to obtain bit allocating information on each audio channel within said block;

(b) means for unpacking quantized frequency coefficients from said block using said bit allocation information; and

(c) means for de-quantizing said quantized frequency coefficients to said frequency coefficients using said cit allocation information.

6. An apparatus according to claim 5, further including means for performing a post-processing process comprising:

(a) means for subjecting said left total mixed down to a window overlap/add process wherein the samples within said left total mixed down are weighted, de-interleaved, overlapped and added to samples of a previous block;

(b) means for subjecting said right total mixed down to a window overlap/add process wherein the samples within said right total mixed down are weighted, de-interleaved, overlapped and added to samples of a previous block; and

(c) means for subjecting the results of said window overlap/add process to an output process where said results of the window overlap/add process are formatted and outputted.