AUDIO DECODER WITH CORE DECODER AND SURROUND DECODER

• US 20170148450A1
• Filed: 02/07/2017
• Published: 05/25/2017
• Est. Priority Date: 04/16/2004
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: PURNHAGEN, Heiko, KJOERLING, Kristofer, VILLEMOES, Lars, ENGDEGARD, Jonas, ROEDEN, Jonas
• Granted Patent: US 10,271,142 B2
• Time in Patent Office: Days
• CPC Class Codes: G10L 19/008 Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/167 Audio streaming, i.e. formatting and decoding of an encoded audio signal representation into a data stream for transmission or storage purposes
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: H04R 5/00 Stereophonic arrangements stereophonic pick-ups H04R9/16, H04R11/12, H04R17/08, H04R19/10
• CPC Class Codes: H04S 2400/01 Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved
• CPC Class Codes: H04S 2400/03 Aspects of down-mixing multi-channel audio to configurations with lower numbers of playback channels, e.g. 7.1 -> 5.1 H04S2400/01 takes precedence
• CPC Class Codes: H04S 2420/03 Application of parametric coding in stereophonic audio systems
• CPC Class Codes: H04S 3/02 of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other
• CPC Class Codes: H04S 5/00 Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation

Abstract

A method performed by an audio decoder for reconstructing N audio channels from an audio signal containing M audio channels is disclosed. The method includes receiving a bitstream containing an encoded audio signal having M audio channels and a set of spatial parameters, the set of spatial parameters including an inter-channel intensity difference parameter and an inter-channel coherence parameter. The encoded audio bitstream is then decoded to obtain a decoded frequency domain representation of the M audio channels, and at least a portion of the frequency domain representation is decorrelated with an all-pass filter having a fractional delay. The all-pass filter is attenuated at locations of a transient. A matrixed version of the decorrelated signals are summed with a matrixed version of the decoded frequency domain representation to obtain N audio signals that collectively having N audio channels where M is less than N.

Claims

1. A method performed in an audio decoder for reconstructing N audio channels from M audio channels, the method comprising:

receiving an encoded audio bitstream, the encoded audio bitstream including a downmixed audio signal and surround data, the downmixed audio signal having M audio channels and the surround data including a set of spatial parameters, the set of spatial parameters including at least one inter-channel intensity difference parameter and at least one inter-channel coherence parameter;

decoding, in a surround data decoder, the surround data to produce decoded surround data;

decoding, in a core decoder, the downmixed audio signal having M audio channels to obtain a decoded frequency domain representation of the M audio channels, wherein the decoded frequency domain representation of the M audio channels includes a plurality of frequency bands, and each frequency band includes one or more spectral components;

reconstructing, in a surround decoder, a frequency domain representation of the N audio channels from the decoded frequency domain representation of the M audio channels, mode information used to select one of a plurality of different mixing schemes, and the decoded surround data; and

synthesizing, with one or more synthesis filterbanks, the frequency domain representation of the N audio channels to create a time domain representation of the N audio channels;

wherein M is one or more, M is less than N, the audio decoder is implemented at least in part with hardware, and the reconstructing includes generating a decorrelated signal using an all-pass filter.

2. The method of claim 1 wherein one or more synthesis filterbanks is a QMF synthesis filterbank.

3. The method of claim 1 further comprising extracting a control parameter from the encoded audio bitstream, the control parameter representing a time resolution or a frequency resolution of inter-channel intensity difference parameter or the inter-channel coherence parameter.

4. The method of claim 3 wherein the time resolution or the frequency resolution varies over time.

5. The method of claim 1 wherein the set of spatial parameters further includes an inter-channel time or phase difference parameter.

6. The method of claim 1 wherein the reconstructing is performed in a frequency domain.

7. The method of claim 1 wherein the inter-channel intensity difference parameter is a ratio between the energy or level of a first channel and a second channel.

8. The method of claim 5 wherein the first channel is a left channel, the second channel is a right channel, M=1 and N=2.

9. The method of claim 1 wherein the M audio channels are a linear down mix of the N audio channels.

10. The method of claim 1 wherein the inter-channel intensity difference parameter and the inter-channel coherence parameter are difference coded over time and the surround data decoder is configured to convert difference coded values to non-difference coded values.

11. The method of claim 1 wherein the inter-channel intensity difference parameter and the inter-channel coherence parameter are difference coded over frequency and the surround data decoder is configured to convert difference coded values to non-difference coded values.

12. The method of claim 1 wherein the core decoder is an MPEG-4 High Efficiency AAC decoder.

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

14. An audio decoder for reconstructing N audio channels from M audio channels, the audio decoder comprising:

an input interface for receiving an encoded audio bitstream, the encoded audio bitstream including a downmixed audio signal and surround data, the downmixed audio signal having M audio channels and the surround data including a set of spatial parameters, the set of spatial parameters including at least one inter-channel intensity difference parameter and at least one inter-channel coherence parameter;

a surround data decoder for decoding the surround data to produce decoded surround data;

a core decoder for decoding the downmixed audio signal having M audio channels to obtain a decoded frequency domain representation of the M audio channels, wherein the decoded frequency domain representation of the M audio channels includes a plurality of frequency bands, and each frequency band includes one or more spectral components;

a surround decoder for reconstructing a frequency domain representation of the N audio channels from the decoded frequency domain representation of the M audio channels, mode information used to select one of a plurality of different mixing schemes, and the decoded surround data; and

one or more synthesis filterbanks for synthesizing the frequency domain representation of the N audio channels to create a time domain representation of the N audio channels, wherein M is one or more and M is less than N and the surround decoder includes an all-pass filter for generating a decorrelated signal.