# US 11,451,920 B2 · Method and device for decoding a higher-order ambisonics (HOA) representation of an audio soundfield

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- Number: US 11,451,920 B2
- Document ID: US11451920B2
- Status: Granted
- Kind: B2
- Application number: 17/189,067
- Filed: 2021-03-01
- Published: 2021-08-19
- Granted: 2022-09-20
- Earliest claimed: 2012-07-16
- Assignees: Dolby Laboratories Licensing Corporation
- Applicants: Dolby Laboratories Licensing Corporation
- Inventors: Johannes Boehm; Florian Keiler
- Web page: https://patentgrep.com/patent/US11451920B2

## CPC

- H04S 7/30: {Control circuits for electronic adaptation of the sound field}
- 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)}
- H04S 2420/11: Application of ambisonics in stereophonic audio systems
- H04S: STEREOPHONIC SYSTEMS

## Abstract

The invention discloses rendering sound field signals, such as Higher-Order Ambisonics (HOA), for arbitrary loudspeaker setups, where the rendering results in highly improved localization properties and is energy preserving. This is obtained by rendering an audio sound field representation for arbitrary spatial loudspeaker setups and/or by a a decoder that decodes based on a decode matrix (D). The decode matrix (D) is based on smoothing and scaling of a first decode matrix {circumflex over (D)} with smoothing coefficients. The first decode matrix {circumflex over (D)} is based on a mix matrix G and a mode matrix {tilde over (ψ)}, where the mix matrix G was determined based on L speakers and positions of a spherical modelling grid related to a HOA order N, and the mode matrix {tilde over (ψ)} was determined based on the spherical modelling grid and the HOA order N.

## Claims

### Claim 1

A method for decoding a Higher-Order Ambisonics (HOA) representation of a sound or sound field, the method comprising:
receiving a smoothed decode matrix {tilde over (D)} that is based on a mix matrix G and a mode matrix {tilde over (ψ)}, wherein the mix matrix G was determined based on L speakers and positions of a spherical modelling grid wherein the mode matrix {tilde over (ψ)} was determined based on the spherical modelling grid and a HOA order N,
wherein the smoothed decode matrix {tilde over (D)} was determined based on smoothing of a first decode matrix {circumflex over (D)} with smoothing coefficients, wherein the first decode matrix {circumflex over (D)} was determined based on {circumflex over (D)}=V Ŝ UH, wherein U,V are based on Unitary matrices, wherein a compact singular value decomposition of a product of the mode matrix with {tilde over (Ψ)} transposed mix matrix is determined based on U S VH={tilde over (ψ)}GT wherein S is based on a diagonal matrix with singular value elements, and wherein Ŝ is a truncated compact singular value decomposition matrix that is either an identity matrix or a modified diagonal matrix, the modified diagonal matrix being determined based on the diagonal matrix with singular value elements by replacing a singular value element that is larger or equal than a threshold by ones, and replacing a singular value element that is smaller than the threshold by zeros,
wherein the smoothing of the smoothed decode matrix {tilde over (D)} is based on a first smoothing method L>O3D, and the smoothing is further based on a second smoothing method L<O3D, wherein O3D=(N+1)2, and rendering coefficients of the HOA representation from a time domain to a spatial domain based on the smoothed decode matrix {tilde over (D)}.

### Claim 2 (depends on 1)

The method of claim 1, further comprising
buffering and serializing a spatial signal W, wherein time samples w(t) for a plurality of channels are obtained; and
delaying time samples w(t) individually for each of the channels in delay lines, wherein corresponding digital signals are obtained,
wherein the delay lines compensate different loudspeaker distances.

### Claim 3 (depends on 1)

A non-transitory computer readable medium having stored thereon executable instructions to cause a computer to perform the method of claim 1.

### Claim 4

An apparatus for decoding a Higher-Order Ambisonics (HOA) representation of a sound or sound field for audio playback, comprising:
a decoder configured to decode coefficients of the HOA sound field representation, the decoder including:
a receiver configured to receive a smoothed decode matrix {tilde over (D)} that is based on a mix matrix G and a mode matrix {tilde over (ψ)}, wherein the mix matrix G was determined based on L speakers and positions of a spherical modelling grid, wherein the mode matrix {tilde over (ψ)} was determined based on the spherical modelling grid and a HOA order N, and
wherein the smoothed decode matrix {tilde over (D)} is determined based on smoothing a first decode matrix {circumflex over (D)} with smoothing coefficients, wherein the first decode matrix {circumflex over (D)} is determined U,V based on {circumflex over (D)}=V Ŝ UH, are based on Unitary matrices,
wherein a compact singular value decomposition of a product of the mode matrix {tilde over (Ψ)} with a transposed mix matrix is determined based on U S VH={tilde over (ψ)}GT, wherein S was determined based on a diagonal matrix with singular value elements, wherein Ŝ is a truncated compact singular value decomposition matrix that is either an identity matrix or a modified diagonal matrix, the modified diagonal matrix being determined based on the diagonal matrix with singular value elements by replacing a singular value element that is larger or equal than a threshold by ones, and replacing a singular value element that is smaller than the threshold by zeros, wherein the smoothing of the decode matrix D is based on a first smoothing method L<O3D, wherein O3D=(N+1)2; and
a renderer configured for rendering coefficients of the HOA representation from a time domain to a spatial domain based on the smoothed decode matrix domain {tilde over (D)}.