# US 10,872,612 B2 · Method and apparatus for determining for the compression of an HOA data frame representation a lowest integer number of bits required for representing non-differential gain values

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- Number: US 10,872,612 B2
- Document ID: US10872612B2
- Status: Granted
- Kind: B2
- Application number: 16/255,358
- Filed: 2019-01-23
- Published: 2019-07-11
- Granted: 2020-12-22
- Earliest claimed: 2014-06-27
- Assignees: Dolby Laboratories Licensing Corporation
- Applicants: Dolby Laboratories Licensing Corporation
- Inventors: Sven Kordon; Alexander Krueger
- Web page: https://patentgrep.com/patent/US10872612B2

## CPC

- G10L 19/008: Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
- H04S 7/30: {Control circuits for electronic adaptation of the sound field}
- H04S 2400/11: Positioning of individual sound objects, e.g. moving airplane, within a sound field (H04S2420/13 takes precedence)
- H04S 2420/11: Application of ambisonics in stereophonic audio systems
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- H04S: STEREOPHONIC SYSTEMS

## Abstract

When compressing an HOA data frame representation, a gain control (15, 151) is applied for each channel signal before it is perceptually encoded (16). The gain values are transferred in a differential manner as side information. However, for starting decoding of such streamed compressed HOA data frame representation absolute gain values are required, which should be coded with a minimum number of bits. For determining such lowest integer number (βe) of bits the HOA data frame representation (C(k)) is rendered in spatial domain to virtual loudspeaker signals lying on a unit sphere, followed by normalisation of the HOA data frame representation (C(k)). Then the lowest integer number of bits is set to βe=┌log2(┌log2(√{square root over (KMAX)}·O)┐+1)┐.

## Claims

### Claim 1

A method of decoding a compressed Higher Order Ambisonics (HOA) sound representation of a sound or sound field, the method comprising:
receiving a bit stream containing the compressed HOA representation, wherein the bitstream includes a number of HOA coefficients corresponding to the compressed HOA representation, and
decoding the compressed HOA representation based on a lowest integer number βe, wherein the lowest integer number βe is determined based on βe=┌log2(┌log2(√{square root over (KMAX)}·O)┐+1)┐,
wherein
KMAX=max1≤N≤NMAXK(N,Ω1(N), . . . ,ΩO(N)),
N is the order, NMAX is a maximum order of interest, Ω1(N), . . . , ΩO(N) are directions of said virtual loudspeakers, O=(N+1) is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥22 of said mode matrix and O,
wherein √{square root over (KMAX)}=1.5.

### Claim 2

An apparatus for decoding a compressed Higher Order Ambisonics (HOA) sound representation of a sound or sound field, the apparatus comprising:
a processor configured to receive a bit stream containing the compressed HOA representation, wherein the bitstream includes a number of HOA coefficients corresponding to the compressed HOA representation, and the processor further configured to decode the compressed HOA representation based on a lowest integer number βe, wherein the lowest integer number βe is determined based on βe=┌log2(┌log2(√{square root over (KMAX)}·O)┐+1)┐,
wherein
KMAX=max1≤N≤NMAXK(N,Ω1(N), . . . , ΩO(N)),
N is the order, NMAX is a maximum order of interest, Ω1(N), . . . , ΩO(N) are directions of said virtual loudspeakers, O=(N+1)2 is the number of HOA coefficient sequences, and K is a ratio between the squared Euclidean norm ∥Ψ∥22 of said mode matrix and O,
wherein √{square root over (KMAX)}=1.5.

### Claim 3 (depends on 1)

A non-transitory computer readable storage medium containing instructions that when executed by a processor perform a method according to claim 1.