# US 8,543,389 B2 · Coding/decoding of digital audio signals

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,543,389 B2
- Document ID: US8543389B2
- Status: Granted
- Kind: B2
- Application number: 12/524,774
- Filed: 2008-01-30
- Published: 2010-05-13
- Granted: 2013-09-24
- Earliest claimed: 2007-02-02
- Assignees: France Telecom
- Applicants: Stéphane Ragot; Cyril Guillaume
- Inventors: Stéphane Ragot; Cyril Guillaume
- Web page: https://patentgrep.com/patent/US8543389B2

## CPC

- G10L 19/0204: {using subband decomposition}
- G10L 19/002: Dynamic bit allocation (for perceptual audio coders G10L19/032)
- G10L 19/0212: {using orthogonal transformation}
- G10L 19/038: Vector quantisation, e.g. TwinVQ audio
- G10L 19/24: Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

The invention relates to the coding/decoding of a signal into several sub-bands, in which at least a first and a second sub-bands which are adjacent are transform coded (601, 602). In particular, in order to apply a perceptual weighting, in the transformed domain, to at least the second sub-band, the method comprises:—determining at least one frequency masking threshold (606) to be applied on the second sub-band; and normalizing said masking threshold in order to provide a spectral continuity between the above-mentioned first and second sub-bands. An advantageous application of the invention involves a perceptual weighting of the high-frequency band in the TDAC transform coding of a hierarchical encoder according to standard G.729.1.

## Claims

### Claim 1

A method of coding an audio signal in several sub-bands, in which at least one first and one second sub-bands which are adjacent are transform coded, wherein, in order to apply a perceptual weighting, in the transformed domain, at least to the second sub-band, the method comprises:
determining at least one frequency masking threshold to be applied on the second sub-band, the same threshold not being applied on the first sub-band, and
normalizing said masking threshold in order to ensure a spectral continuity between said first and second sub-bands,
to produce a coded audio signal.

### Claim 2 (depends on 1)

A method according to claim 1, in which a number of bits to be allocated to each sub-band is determined on the basis of a spectral envelope, wherein the bit allocation for the second sub-band at least is determined moreover as a function of a normalized masking curve computation, applied at least to the second sub-band.

### Claim 3 (depends on 2)

A method according to claim 2, in which the coding is carried out on more than two sub-bands, the first sub-band being included in a first spectral band and the second sub-band being included in a second spectral band, wherein the number of bits per sub-band nbit(j) is given, for each sub-band of index j, according to a perceptual importance ip(j) computed on the basis of a relationship of the type:
ip
⁡
(
j
)
=
1
2
⁢
rms_index
⁢
(
j
)
,
if j is a sub-band index in the first band, and
ip
⁡
(
j
)
=
1
2
⁡
[
rms_index
⁢
(
j
)
-
log_mask
⁢
(
j
)
]
,
if j is a sub-band index in the second band, with log_mask(j)=log2(M(j))-normfac, where:
rms13 index(j) are quantized values originating from the coding of the envelope, for the sub-band j,
M(j) is the masking threshold for said sub-band of index j, and
normfac is a normalization factor determined to ensure spectral continuity between said first and second sub-bands.

### Claim 4 (depends on 1)

A method according to claim 1, wherein the transformed signal, in the second sub-band, is weighted by a factor proportional to the square root of the normalized masking threshold for the second sub-band.

### Claim 5 (depends on 4)

A method according to claim 4, in which the coding is carried out on more than two sub-bands, the first sub-band being included in a first spectral band and the second sub-band being included in a second spectral band, wherein weighting values of √{square root over (M(j))} are coded, where M(j) is the normalized masking threshold for a sub-band of index j, included in the second spectral band.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the transform coding takes place in an upper layer of a hierarchical coder,
the first sub-band comprising a signal originating from a core coding of the hierarchical coder,
and the second sub-band comprising an original signal.

### Claim 7 (depends on 6)

A method according to claim 6, wherein the signal originating from the core coding is perceptually weighted.

### Claim 8 (depends on 6)

A method according to claim 6, wherein the signal originating from the core coding is a signal representing a difference between an original signal and a synthesis of this original signal.

### Claim 9 (depends on 6)

A method according to claim 6, wherein the transform coding is of the TDAC type in an overall coder according to standard G.729.1, and the first sub-band is included in a low-frequency band, while the second sub-band is included in a high-frequency band.

### Claim 10 (depends on 9)

A method according to claim 9, wherein the high-frequency band extends up to 7000 Hz, at least.

### Claim 11 (depends on 1)

A method according to claim 1, in which a spectral envelope is computed, wherein the masking threshold, for a sub-band, is defined by a convolution between:
an expression of the spectral envelope, and
a spread function involving a central frequency of said sub-band.

### Claim 12 (depends on 1)

A method according to claim 1, in which information is obtained according to which the signal to be coded is tonal or not tonal, wherein the perceptual weighting of the second sub-band, with determination of the masking threshold and the normalization, are only carried on if the signal is not tonal.

### Claim 13

A method of decoding an audio signal in several sub-bands, in which at least one first and one second sub-bands which are adjacent are transform decoded, wherein, in order to apply a perceptual weighting, in the transformed domain, at least to the second sub-band, the method comprises:
a determination of at least one frequency masking threshold to apply on the second sub-band, on the basis of a decoded spectral envelope, the same threshold not being applied on the first sub-band, and
a normalization of said masking threshold in order to ensure a spectral continuity between said first and second sub-bands,
to produce a decoded audio signal.

### Claim 14 (depends on 13)

A method according to claim 13, in which a number of bits to be allocated to each sub-band is determined on the basis of a decoding of spectral envelope, wherein the bit allocation for the second sub-band at least is determined moreover according to a normalized masking curve computation, applied at least to the second sub-band.

### Claim 15 (depends on 13)

A method according to claim 13, wherein the transformed signal, in the second sub-band, is weighted by a factor proportional to the square root of the normalized masking threshold for the second sub-band.

### Claim 16 (depends on 1)

A non-transitory storage medium, comprising a memory of a coder of a telecommunications terminal and/or a storage medium intended to cooperate with a reader of said coder, storing a software program comprising instructions for the implementation of the coding method according to claim 1 when said instructions are executed by a processor of the coder.

### Claim 17

A coder for coding a signal in several sub-bands, at least one first and one second sub-bands which are adjacent being transform coded, wherein, in order to apply a perceptual weighting, in the transformed domain, at least to the second sub-band, the coder comprises means for:
determining at least one frequency masking threshold to be applied on the second sub-band, the same threshold not being applied on the first sub-band, and
normalizing said masking threshold in order to ensure a spectral continuity between said first and second sub-bands.

### Claim 18 (depends on 13)

A non-transitory storage medium, comprising a memory of a decoder of a telecommunications terminal and/or a storage medium intended to cooperate with a reader of said decoder, storing a software program comprising instructions for the implementation of the decoding method according to claim 13 when said instructions are executed by a processor of the decoder.

### Claim 19

A decoder for decoding a signal in several sub-bands, at least one first and one second sub-bands which are adjacent being transform decoded, wherein, in order to apply a perceptual weighting, in the transformed domain, at least to the second sub-band, the decoder comprises means for:
determining at least one frequency masking threshold to apply on the second sub-band, on the basis of a decoded spectral envelope, the same threshold not being applied on the first sub-band, and
normalizing said masking threshold in order to ensure a spectral continuity between said first and second sub-bands.