Reduction of comb filter artifacts in multi-channel downmix with adaptive phase alignment

Patent metadata

Field	Value
Publication number	US-2016133262-A1
Application number	US-201615000508-A
Country	US
Kind code	A1
Filing date	Jan 19, 2016
Priority date	Jul 22, 2013
Publication date	May 12, 2016
Grant date	—

Abstract

An audio signal processing decoder having at least one frequency band and being configured for processing an input audio signal having a plurality of input channels in the at least one frequency band, wherein the decoder is configured to analyze the input audio signal, wherein inter-channel dependencies between the input channels are identified; and to align the phases of the input channels based on the identified inter-channel dependencies, wherein the phases of input channels are the more aligned with respect to each other the higher their inter-channel dependency is; and to downmix the aligned input audio signal to an output audio signal having a lesser number of output channels than the number of the input channels.

First claim

1 . An audio signal processing decoder comprising at least one frequency band and being configured for processing an input audio signal comprising a plurality of input channels in the at least one frequency band, wherein the decoder is configured
to align the phases of the input channels depending on inter-channel dependencies between the input channels, wherein the phases of input channels are the more aligned with respect to each other the higher their inter-channel dependency is; and to downmix the aligned input audio signal to an output audio signal comprising a lesser number of output channels than the number of the input channels.

2 . The decoder according to claim 1 , wherein the decoder is configured to analyze the input audio signal in the frequency band, in order to identify the inter-channel dependencies between the input audio channels or to receive the inter-channel dependencies between the input channels from an external device, such as from an encoder, which provides the input audio signal.

3 . The decoder according to claim 1 , wherein the decoder is configured to normalize the energy of the output audio signal based on a determined energy of the input audio signal, wherein the decoder is configured to determine the signal energy of the input audio signal or to receive the determined energy of the input audio signal from an external device, such as from an encoder, which provides the input audio signal.

4 . The decoder according to claim 1 , wherein the decoder comprises a downmixer for downmixing the input audio signal based on a downmix matrix, wherein the decoder is configured to calculate the downmix matrix, in such way that the phases of the input channels are aligned based on the identified inter-channel dependencies or to receive a downmix matrix calculated in such way that the phases of the input channels are aligned based on the identified inter-channel dependencies from an external device, such as from an encoder, which provides the input audio signal.

5 . The decoder according to claim 4 , wherein the decoder is configured to calculate the downmix matrix in such way that the energy of the output audio signal is normalized based on the determined energy of the input audio signal or to receive the downmix matrix, calculated in such way that the energy of the output audio signal is normalized based on the determined energy of the input audio signal from an external device, such as from an encoder, which provides the input audio signal.

6 . The decoder according to claim 1 , wherein the decoder is configured to analyze time intervals of the input audio signal using a window function, wherein the inter-channel dependencies are determined for each time frame or wherein the decoder is configured to receive an analysis of time intervals of the input audio signal using a window function, wherein the inter-channel dependencies are determined for each time frame, from an external device, such as from an encoder, which provides the input audio signal.

7 . The decoder according to claim 1 , wherein the decoder is configured to calculate a covariance value matrix, wherein the covariance values express the inter-channel dependency of a pair of input audio channels or wherein the decoder is configured to receive a covariance value matrix, wherein the covariance values express the inter-channel dependency of a pair of input audio channels, from an external device, such as from an encoder, which provides the input audio signal.

8 . The decoder according to claim 7 , wherein the decoder is configured to establish an attraction value matrix by applying a mapping function to the covariance value matrix or to a matrix derived from the covariance value matrix or to receive an attraction value matrix established by applying a mapping function to the covariance value matrix or to a matrix derived from the covariance value matrix, wherein the gradient of the mapping function is preferably bigger or equal to zero for all covariance values or values derived from the covariance values and wherein the mapping function preferably reaches values between zero and one for input values between zero and one.

9 . The decoder according to claim 8 , wherein the mapping function is a non-linear function.

10 . The decoder according to claim 8 , wherein the mapping function is equal to zero for covariance values or values derived from the covariance values being smaller than a first mapping threshold and/or wherein the mapping function is equal to one for covariance values or values derived from the covariance values being bigger than a second mapping threshold.

11 . The decoder according to claim 8 , wherein the mapping function is represented by a function forming an S-shaped curve.

12 . The decoder according to claim 7 , wherein the decoder is configured to calculate a phase alignment coefficient matrix, wherein the phase alignment coefficient matrix is based on the covariance value matrix and on a prototype downmix matrix or to receive a phase alignment coefficient matrix, wherein the phase alignment coefficient matrix is based on the covariance value matrix and on a prototype downmix matrix, from an external device, such as from an encoder, which provides the input audio signal.

13 . The decoder according to claim 12 , wherein the phases and/or the amplitudes of the downmix coefficients of the downmix matrix are formulated to be smooth over time, so that temporal artifacts due to signal cancellation between adjacent time frames are avoided.

14 . The decoder according to claim 12 , wherein the phases and/or the amplitudes of the downmix coefficients of the downmix matrix are formulated to be smooth over frequency, so that spectral artifacts due to signal cancellation between adjacent frequency bands are avoided.

15 . The decoder according to claim 12 , wherein the decoder is configured to establish a regularized phase alignment coefficient matrix based on the phase alignment coefficient matrix or to receive a regularized phase alignment coefficient matrix based on the phase alignment coefficient matrix from an external device, such as from an encoder, which provides the input audio signal.

16 . The decoder according to claim 15 , wherein the downmix matrix is based on the regularized phase alignment coefficient matrix.

17 . An audio signal processing encoder comprising at least one frequency band and being configured for processing an input audio signal comprising a plurality of input channels in the at least one frequency band, wherein the encoder is configured
to align the phases of the input channels depending on inter-channel dependencies between the input channels, wherein the phases of input channels are the more aligned with respect to each other the higher their inter-channel dependency is; and to downmix the aligned input audio signal to an output audio signal comprising a lesser number of output channels than the number of the input channels.

18 . An audio signal processing encoder comprising at least one frequency band and being configured for outputting a bitstream, wherein the bitstream comprises an encoded audio signal in the frequency band, wherein the encoded audio signal comprises a plurality of encoded channels in the at least one frequency band, wherein the encoder is configured
to calculate a downmix matrix for a downmixer for downmixing the encoded audio signal based on the downmix matrix in such way that the phases of the encoded channels are aligned based on identified inter-channel dependencies, preferably in such way that the energy of an out

Assignees

• Fraunhofer Ges Forschung

Inventors

• Füg Simone
• Kuntz Achim
• Kratschmer Michael
• Vilkamo Juha

Classifications

• H04S3/02

  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 title

• 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

• G10L19/005

  Correction of errors induced by the transmission channel, if related to the coding algorithm · CPC title

• G10L21/04

  Time compression or expansion · CPC title

• H04S2400/03

  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 title