# US 11,451,918 B2 · Method for and apparatus for decoding/rendering an Ambisonics audio soundfield representation for audio playback using 2D setups

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- Number: US 11,451,918 B2
- Document ID: US11451918B2
- Status: Granted
- Kind: B2
- Application number: 17/231,291
- Filed: 2021-04-15
- Published: 2021-09-30
- Granted: 2022-09-20
- Earliest claimed: 2013-10-23
- Assignees: Dolby Laboratories Licensing Corporation
- Applicants: Dolby Laboratories Licensing Corporation
- Inventors: Florian Keiler; Johannes Boehm
- Web page: https://patentgrep.com/patent/US11451918B2

## CPC

- 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 7/308: {Electronic adaptation dependent on speaker or headphone connection}
- H04S 2400/11: Positioning of individual sound objects, e.g. moving airplane, within a sound field (H04S2420/13 takes precedence)
- H04S 2420/07: Synergistic effects of band splitting and sub-band processing
- H04S 2420/11: Application of ambisonics in stereophonic audio systems
- H04S: STEREOPHONIC SYSTEMS

## Abstract

Improved methods and/or apparatus for decoding an encoded audio signal in soundfield format for L loudspeakers. The method and/or apparatus can render an Ambisonics format audio signal to 2D loudspeaker setup(s) based on a rendering matrix. The rendering matrix has elements based on loudspeaker positions and wherein the rendering matrix is determined based on weighting at least an element of a first matrix with a weighting factor g = 1 L . The first matrix is determined based on positions of the L loudspeakers and at least a virtual position of at least a virtual loudspeaker that is added to the positions of the L loudspeakers.

## Claims

### Claim 1

A method of determining a decode matrix ({tilde over (D)}) for decoding an encoded audio signal, the encoded audio signal being in Ambisonics format for L loudspeakers, the method comprising:
determining a set of loudspeaker positions comprising at least one virtual loudspeaker position ({circumflex over (Ω)}′L+1) and the positions ({circumflex over (Ω)}1, . . . , {circumflex over (Ω)}L) of the L loudspeakers;
determining a first matrix (D′) having coefficients for the positions of the set of loudspeaker positions; and
determining the decode matrix ({tilde over (D)}) from the first matrix (D′), at least by weighting and distributing the coefficient(s) for the at least one virtual loudspeaker position of the first matrix (D′) to coefficients relating to the positions ({circumflex over (Ω)}1, . . . , {circumflex over (Ω)}L) of the L loudspeakers, whereby the decode matrix ({tilde over (D)}) has coefficients for the positions ({circumflex over (Ω)}1, . . . , {circumflex over (Ω)}L) of the L loudspeakers,
wherein said weighting and distributing the coefficient(s) for the at least one virtual loudspeaker position of the first matrix (D′) comprises weighting said coefficient(s) with a
weighting
⁢
⁢
factor
⁢
=
1
L
.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
separating the encoded audio signal into a plurality of frequency bands using band pass filters; and
determining respective first matrices (Db′) for the plurality of frequency bands; and
determining respective decode matrices from a plurality of first matrices, for separately decoding each frequency band of the plurality of frequency bands of the encoded audio signal.

### Claim 3 (depends on 1)

The method of claim 1, wherein an L loudspeaker positions are substantially within one 2D plane, with elevations of not more than 10°.

### Claim 4 (depends on 1)

An apparatus for determining a decode matrix ({tilde over (D)}) for decoding an encoded audio signal, the encoded audio signal being in Ambisonics format for L loudspeakers, the apparatus comprising at least one processor and at least one memory, the memory having stored instructions that when executed on the at least one processor cause the apparatus to perform the method of claim 1.

### Claim 5 (depends on 1)

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