# US 2019/0320280 A1 · Method and device for applying dynamic range compression to a higher order ambisonics signal

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- Number: US 2019/0320280 A1
- Document ID: US20190320280A1
- Status: Published application
- Kind: A1
- Application number: 16/457,135
- Filed: 2019-06-28
- Published: 2019-10-17
- Earliest claimed: 2014-03-24
- Assignees: Dolby Laboratories Licensing Corporation
- Applicants: Dolby Laboratories Licensing Corporation
- Inventors: Johannes BOEHM; Florian KEILER
- Web page: https://patentgrep.com/patent/US20190320280A1

## CPC

- 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 19/008: Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
- 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
- H04S 2420/01: Enhancing the perception of the sound image or of the spatial distribution using head related transfer functions [HRTF's] or equivalents thereof, e.g. interaural time difference [ITD] or interaural level difference [ILD]
- H04S 2420/11: Application of ambisonics in stereophonic audio systems
- H04S: STEREOPHONIC SYSTEMS
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

A method for performing DRC on a HOA signal comprises transforming the HOA signal to the spatial domain, analyzing the transformed HOA signal, and obtaining, from results of said analyzing, gain factors that are usable for dynamic compression. The gain factors can be transmitted together with the HOA signal. When applying the DRC, the HOA signal is transformed to the spatial domain, the gain factors are extracted and multiplied with the transformed HOA signal in the spatial domain, wherein a gain compensated transformed HOA signal is obtained. The gain compensated transformed HOA signal is transformed back into the HOA domain, wherein a gain compensated HOA signal is obtained. The DRC may be applied in the QMF-filter bank domain.

## Claims

### Claim 1

A method for dynamic range compression (DRC), the method comprising:
receiving a reconstructed Higher Order Ambisonics (HOA) audio signal representation;
transforming the reconstructed HOA audio signal into a spatial domain based on:
WDSHT=DDSHTC, wherein DDSHT is an inverse Discrete Spherical Harmonics Transform (DSHT) matrix, wherein C is a block of τ HOA samples, and
wherein W is a block of spatial samples matching an input time granularity of a Quadrature Mirror Filter (QMF) bank;
applying a DRC gain value g(n, m) corresponding to a time frequency tile (n, m) based on:
{hacek over (w)}DRC(n,m)=diag(g(n,m))ŵDSHT(n,m),
wherein ŵDSHT(n, m) is a vector of spatial channels for the time frequency tile (n, m); and
rendering to loudspeaker channels based on:
w(n, m)=D DDSHT−1 {hacek over (w)}DRC(n, m), wherein DDSHT−1 matrix is an inverse of the DDSHT matrix and D is a HOA rendering matrix,
wherein the DDSHT−1 the DDSHT matrices are optimized for DRC purposes.

### Claim 2

An apparatus for dynamic range compression (DRC), the apparatus comprising:
a receiver for receiving a reconstructed Higher Order Ambisonics (HOA) audio signal representation;
an audio decoder configured to:
transform the reconstructed HOA audio signal into a spatial domain based on:
WDSHT=DDSHTC, wherein DDSHT is an inverse Discrete Spherical Harmonics Transform (DSHT) matrix, wherein C is a block of τ HOA samples, and wherein W is a block of spatial samples matching an input time granularity of a Quadrature Mirror Filter (QMF) bank;
apply a DRC gain value g(n, m) corresponding to a time frequency tile (n, m) based on:
{hacek over (w)}DRC(n, m)=diag(g(n, m)) ŵDSHT (n, m), wherein ŵDSHT(n, m) is a vector of spatial channels for the time frequency tile (n, m); and
rendering to loudspeaker channels based on w(n, m)=D DDSHT−1 {hacek over (w)}DRC(n, m), wherein DDSHT−1 matrix is an inverse of the DDSHT matrix and D is a HOA rendering matrix,
wherein the DDSHT−1 and the DDSHT matrices are optimized for DRC purposes.

### Claim 3 (depends on 1)

A non-transitory computer readable storage medium having computer executable instructions that when executed on a computer cause the computer to perform the method of claim 1.