# US 9,520,135 B2 · Reconstructing audio signals with multiple decorrelation techniques

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- Number: US 9,520,135 B2
- Document ID: US9520135B2
- Status: Granted
- Kind: B2
- Application number: 15/060,425
- Filed: 2016-03-03
- Published: 2016-06-30
- Granted: 2016-12-13
- Earliest claimed: 2004-03-01
- Assignees: Dolby Laboratories Licensing Corporation
- Applicants: Dolby Laboratories Licensing Corporation
- Inventors: Mark F. Davis
- Web page: https://patentgrep.com/patent/US9520135B2

## CPC

- G10L 19/06: Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
- G10L 19/005: Correction of errors induced by the transmission channel, if related to the coding algorithm
- G10L 19/008: Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
- G10L 19/018: Audio watermarking, i.e. embedding inaudible data in the audio signal
- G10L 19/02: using spectral analysis, e.g. transform vocoders or subband vocoders
- G10L 19/0204: {using subband decomposition}
- G10L 19/025: Detection of transients or attacks for time/frequency resolution switching
- G10L 19/26: Pre-filtering or post-filtering
- H04S 3/00: Systems employing more than two channels, e.g. quadraphonic (H04S5/00, H04S7/00 take precedence)
- H04S 3/008: {in which the audio signals are in digital form, i.e. employing more than two discrete digital channels (data reduction aspects thereof based on psychoacoustics G10L19/02)}
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- H04S: STEREOPHONIC SYSTEMS

## 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.

## Claims

### Claim 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;
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;
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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 1)

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.

### Claim 5 (depends on 1)

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

### Claim 6 (depends on 1)

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.

### Claim 7 (depends on 6)

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

### Claim 8 (depends on 1)

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

### Claim 9 (depends on 1)

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.

### Claim 10 (depends on 1)

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

### Claim 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;
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 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.