Method and apparatus for generating from a coefficient domain representation of HOA signals a mixed spatial/coefficient domain representation of said HOA signals

Patent metadata

Field	Value
Publication number	US-9668079-B2
Application number	US-201414904406-A
Country	US
Kind code	B2
Filing date	Jun 24, 2014
Priority date	Jul 11, 2013
Publication date	May 30, 2017
Grant date	May 30, 2017

Abstract

There are two representations for Higher Order Ambisonics denoted HOA: spatial domain and coefficient domain. The invention generates from a coefficient domain representation a mixed spatial/coefficient domain representation, wherein the number of said HOA signals can be variable. A vector of coefficient domain signals is separated into a vector of coefficient domain signals having a constant number of HOA coefficients and a vector of coefficient domain signals having a variable number of HOA coefficients. The constant-number HOA coefficients vector is transformed to a corresponding spatial domain signal vector. In order to facilitate high-quality coding, without creating signal discontinuities the variable-number HOA coefficients vector of coefficient domain signals is adaptively normalized and multiplexed with the vector of spatial domain signals.

First claim

The invention claimed is:

1. A method for generating from a coefficient domain representation of HOA signals a mixed spatial/coefficient domain representation of said HOA signals, wherein a number of said HOA signals can be variable over time in successive coefficient frames, said method comprising:
separating a vector of HOA coefficient domain signals into a first vector of coefficient domain signals having a constant number of HOA coefficients and a second vector of coefficient domain signals having over time a variable number of HOA coefficients;
transforming said first vector of coefficient domain signals to a corresponding vector of spatial domain signals by multiplying said vector of coefficient domain signals with an inverse of a transform matrix;
PCM encoding said vector of spatial domain signals to determine a vector of PCM encoded spatial domain signals;
normalizing said second vector of coefficient domain signals by a normalization factor, wherein said normalizing is an adaptive normalization with respect to a current value range of HOA coefficients of said second vector of coefficient domain signals and in said normalizing an available value range for HOA coefficients of the vector is not exceeded, and in which normalization a uniformly continuous transition function is applied to the coefficients of said second vector, which thereafter represents a current second vector, in order to continuously change a first gain within that current second vector from a second gain in a previous second vector to a third gain in a following second vector, and which normalization provides side information for a corresponding decoder-side de-normalization;
PCM encoding said current second vector of normalized coefficient domain signals to determine a vector of PCM encoded and normalized coefficient domain signals;
multiplexing said vector of PCM encoded spatial domain signals and said vector of PCM encoded and normalized coefficient domain signals.

2. The method according to claim 1 , wherein said normalization comprises:
multiplying each coefficient of said current second vector by a gain value that was kept from a previous second vector normalization processing;
determining from the resulting normalized second vector a maximum of the absolute values;
applying a temporal smoothing to said maximum value by using a recursive filter receiving a previous value of said smoothed maximum, resulting in a current temporally smoothed maximum value, wherein said temporal smoothing is only applied if said maximum value lies within a pre-defined value range, otherwise said maximum value is taken as it is;
computing from said current temporally smoothed maximum value a normalization gain as an exponent to the base of ‘2’, thereby obtaining a quantized exponent value;
applying said quantized exponent value to a transition function so as to get a current gain value, wherein said transition function serves for a continuous transition from said previous gain value to said current gain value;
weighting each coefficient of a previous second vector by said transition function so as to get said normalized second vector of coefficient domain signals.

3. The method according to claim 2 , wherein said current temporally smoothed maximum value is calculated by:

x

n
,
max
,
sm

⁡

(

j
-
1

)

=

{

x

n
,
max

for
⁢

⁢

x

n
,
max

≥
1

(

1
-
a

)

⁢

x

n
,
max
,
sm

⁡

(

j
-
1

)

+

a
⁢

⁢

x

n
,
max

otherwise

,

wherein x n,max denotes said maximum value, 0<a≦1 is an attenuation constant, and j is a running index of an input matrix of HOA signal vectors.

4. The method according to claim 1 , further comprising perceptually encoding multiplexed HOA signals resulting from the multiplexing said vector of PCM encoded spatial domain signals and said vector of PCM encoded and normalized coefficient domain signals.

5. An apparatus for generating from a coefficient domain representation of HOA signals a mixed spatial/coefficient domain representation of said HOA signals, wherein a number of said HOA signals can be variable over time in successive coefficient frames, said apparatus comprising:
means adapted for separating a vector of HOA coefficient domain signals to determine so as to into a first vector of coefficient domain signals having a constant number of HOA coefficients and a second vector of coefficient domain

Assignees

• Dolby Laboratories Licensing Corp
• Dobly Laboratories Licensing Corp

Inventors

• Kordon Sven
• Krueger Alexander

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 Primary

  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

• H04S2420/11

  Application of ambisonics in stereophonic audio systems · CPC title

• H04S3/00

  Systems employing more than two channels, e.g. quadraphonic (H04S5/00, H04S7/00 take precedence) · CPC title