Reconstructing audio signals with multiple decorrelation techniques

Patent metadata

Field	Value
Publication number	US-9640188-B2
Application number	US-201615344137-A
Country	US
Kind code	B2
Filing date	Nov 4, 2016
Priority date	Mar 1, 2004
Publication date	May 2, 2017
Grant date	May 2, 2017

Abstract

A method performed in an audio decoder for decoding M encoded audio channels representing N audio channels is disclosed. The method includes receiving a bitstream containing the M encoded audio channels and a set of spatial parameters, decoding the M encoded audio channels, and extracting the set of spatial parameters from the bitstream. The method also includes analyzing the M audio channels to detect a location of a transient, decorrelating the M audio channels, and deriving N audio channels from the M audio channels and the set of spatial parameters. A first decorrelation technique is applied to a first subset of each audio channel and a second decorrelation technique is applied to a second subset of each audio channel. The first decorrelation technique represents a first mode of operation of a decorrelator, and the second decorrelation technique represents a second mode of operation of the decorrelator.

First claim

The invention claimed is:

1. A method performed in an audio decoder for reconstructing N audio channels from an audio signal having M audio channels, the method comprising:
receiving a bitstream containing the M audio channels and a set of spatial parameters, wherein the set of spatial parameters includes an amplitude parameter and a correlation parameter, wherein the amplitude parameter is differentially encoded across time;
decoding the M encoded audio channels, wherein each audio channel is divided into a plurality of frequency bands, and each frequency band includes one or more spectral components;
extracting the set of spatial parameters from the bitstream;
applying a differential decoding process across time to the differentially encoded amplitude parameter to obtain a differentially decoded amplitude parameter;
analyzing the M audio channels to detect a location of a transient;
decorrelating the M audio channels to obtain a decorrelated version of the M audio channels, wherein a first decorrelation technique is applied to a first subset of the plurality of frequency bands of each audio channel and a second decorrelation technique is applied to a second subset of the plurality of frequency bands of each audio channel;
deriving N audio channels from the M audio channels, the decorrelated version of the M audio channels, and the set of spatial parameters, wherein N is two or more, M is one or more, and M is less than N; and
synthesizing, by an audio reproduction device, the N audio channels as an output audio signal,
wherein both the analyzing and the decorrelating are performed in a frequency domain, the first decorrelation technique represents a first mode of operation of a decorrelator, the second decorrelation technique represents a second mode of operation of the decorrelator, and the audio decoder is implemented at least in part in hardware.

2. The method of claim 1 wherein the first mode of operation uses an all-pass filter and the second mode of operation uses a fixed delay.

3. The method of claim 1 wherein the analyzing occurs after the extracting and the deriving occurs after the decorrelating.

4. The method of claim 1 wherein the first subset of the plurality of frequency bands is at a higher frequency than the second subset of the plurality of frequency bands.

5. The method of claim 1 wherein the M audio channels are a sum of the N audio channels.

6. The method of claim 1 wherein the location of the transient is used in the decorrelating to process bands with a transient differently than bands without a transient.

7. The method of claim 6 wherein the N audio channels represent a stereo audio signal where N is two and M is one.

8. The method of claim 1 wherein the N audio channels represent a stereo audio signal where N is two and M is one.

9. The method of claim 1 wherein the first subset of the plurality of frequency bands is non-overlapping but contiguous with the second subset of the plurality of frequency bands.

10. A non-transitory computer readable medium containing instructions that when executed by a processor perform the method of claim 1 .

11. An audio decoder for decoding M encoded audio channels representing N audio channels, the audio decoder comprising:
an input interface for receiving a bitstream containing the M encoded audio channels and a set of spatial parameters, wherein the set of spatial parameters includes an amplitude parameter and a correlation parameter, wherein the amplitude parameter is differentially encoded across time;
an audio decoder for decoding the M encoded audio channels, wherein each audio channel is divided into a plurality of frequency bands, and each frequency band includes one or more spectral components;
a demultiplexer for extracting the set of spatial parameters from the bitstream;
a processor for applying a differential decoding process across time to the differentially encoded amplitude parameter to obtain a differentially decoded amplitude parameter, and analyzing the M audio channels to detect a location of a transient;
a decorrelator for decorrelating the M audio channels, wherein a first decorrelation technique is applied to a first subset of the plurality of frequency bands of each audio channel and a second decorrelation technique is applied to a second subset of the plurality of frequency bands of each audio channel;
a reconstructor for deriving N audio channels from the M audio channels and the set of spatial parameters, wherein N is two or more, M is one or more, and M is less than N; and
an audio reproduction device that synthesizes the N audio channels as an output audio signal,
wherein both the analyzing and the decorrelating are performed in a frequency domain, the first decorrelation technique represents a first mode of operation of a decorrelator, and the second decorrelation technique represents a second mode of operation of the decorrelator.

Assignees

• Dolby Laboratories Licensing Corp

Inventors

• Davis Mark F

Classifications

• G10L19/008 Primary

  Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing · CPC title

• G10L19/0204

  using subband decomposition · CPC title

• G10L19/018

  Audio watermarking, i.e. embedding inaudible data in the audio signal · CPC title

• H04S3/00

  Systems employing more than two channels, e.g. quadraphonic (H04S5/00, H04S7/00 take precedence) · CPC title

• G10L19/02

  using spectral analysis, e.g. transform vocoders or subband vocoders · CPC title