Method and apparatus for converting a channel-based 3D audio signal to an HOA audio signal

Patent metadata

Field	Value
Publication number	US-10600425-B2
Application number	US-201615771084-A
Country	US
Kind code	B2
Filing date	Nov 16, 2016
Priority date	Nov 17, 2015
Publication date	Mar 24, 2020
Grant date	Mar 24, 2020

Abstract

A system for converting a channel-based 3D audio signal to a higher-order Ambisonics HOA audio signal, the channel-based 3D audio signal is transformed from time domain to frequency domain. A primary ambient decomposition is carried out for three-channel triplets of blocks of the domain channel-based 3D audio signal, wherein directional signals and ambient signals are provided for each triplet. From the directional signals directional information of a total directional signal for each triple is derived. That total directional signal is HOA encoded according to the derived directions, and ambient signals are HOA encoded according to channel positions. The HOA coefficients of the HOA encoded directional signal and the HOA coefficients of the HOA encoded ambient signal are superimposed in order to obtain a HOA coefficients signal for the channel-based 3D audio signal, followed by a transformation into time domain.

First claim

The invention claimed is:

1. A method for converting a channel-based 3D audio signal to a higher-order Ambisonics HOA audio signal, said method including:
if said channel-based 3D audio signal is in time domain, transforming said channel-based 3D audio signal from time domain to frequency domain;
carrying out a primary ambient decomposition for three-channel triplets of blocks of said frequency domain channel-based 3D audio signal, wherein related directional signals and ambient signals are provided for each triplet, and wherein said primary ambient decomposition includes a directional and ambient power estimation, a linear spectral estimation based on minimum mean square error principle, and a post-scaling of the estimated spectra such that power maintenance is achieved;
from said directional signals, deriving directional information of a total directional signal for each triplet;
HOA encoding said total directional signal according to said derived directions, and HOA encoding ambient signals according to channel positions;
superimposing HOA coefficients of said HOA encoded directional signal and HOA coefficients of said HOA encoded ambient signal in order to obtain an HOA coefficients signal for said channel-based 3D audio signal;
transforming said HOA coefficients signal to time domain.

2. The method of claim 1 , wherein windowing and overlapping is carried out in connection with said transform from time domain to frequency domain, while windowing and overlap-add is carried out in connection with said transform from frequency, domain to time domain.

3. The method of claim 1 , wherein, in case there are more than three channels, a triangulation is performed in that channels of said channel-based 3D audio signal are divided into non-overlapping triangles or triplets with three-channel positions as vertices.

4. The method of claim 3 , wherein in case the channel positions of said channel-based 3D audio signal are given in 3D space on a unit sphere, said triangulation is accomplished by means of a Delaunay triangulation using the Quickhull algorithm.

5. The method of claim 1 , wherein said primary ambient decomposition for said triplets is carried out successively and the decomposition order is carried out according to triplet powers, such that a triplet with a higher total power is decomposed earlier than a triplet with a lower total power, wherein the total power is the sum of three channel powers belonging to a triplet.

6. The method of claim 1 , wherein based on the decomposition order, said primary ambient decomposition is carried out for individual triplets, thereby delivering directional and ambient signals of three channels, and wherein three directional signals are combined to a total directional signal according to the principle of summing localisation, while the directions are derived by means of panning laws.

7. The method of claim 1 , wherein said primary ambient decomposition includes:
calculating, for a block (X m [i]) of multichannel spectral bins, signal powers P m [i] and inter-channel cross correlations c mn [i] between different channel signals, wherein 1≤m≤3 denotes a specific triplet after triangulation, m,n denote two different channels and i denotes a frequency bin index;
calculating a directional signal power

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if calculated said signal power P m [i] is smaller than directional power P S m [i], post-processing said directional power P S m [i] such that it is less than P m [i] and approaches P S m [i] as far as possible;
calculating a band signal power P m,b , a band-wise inter-channel cross correlation c mn,b , a directional band power P S m ,b and an ambient band power σ m,b 2 =P m,b −P S m ,b , wherein b denotes a band;
calculating a primary-to-ambient ratio PAR m [i]=P S m [i]/σ m 2 [i] for each individual channel and their sum

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or calculating a primary-to-ambient ratio PAR m,b =P S m ,b /σ m,b 2 for each individual band and their sum

Assignees

• Dolby Laboratories Licensing Corp

Inventors

• Boehm Johannes
• Chen Xiaoming

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

• H04S3/008

  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) · CPC title