# US 10,121,486 B2 · Audio signal classification and coding

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- Number: US 10,121,486 B2
- Document ID: US10121486B2
- Status: Granted
- Kind: B2
- Application number: 15/797,725
- Filed: 2017-10-30
- Published: 2018-02-15
- Granted: 2018-11-06
- Earliest claimed: 2014-05-15
- Assignees: Telefonaktiebolaget LM Ericsson
- Applicants: Telefonaktiebolaget LM Ericsson (publ)
- Inventors: Erik Norvell; Stefan Bruhn
- Web page: https://patentgrep.com/patent/US10121486B2

## CPC

- G10L 19/20: using sound class specific coding, hybrid encoders or object based coding
- G10L 25/18: the extracted parameters being spectral information of each sub-band
- 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 a codec and a signal classifier and methods therein for signal classification and selection of a coding mode based on audio signal characteristics. A method embodiment to be performed by a decoder comprises, for a frame m: determining a stability value D(m) based on a difference, in a transform domain, between a range of a spectral envelope of frame m and a corresponding range of a spectral envelope of an adjacent frame m−1. Each such range comprises a set of quantized spectral envelope values related to the energy in spectral bands of a segment of the audio signal. The method further comprises selecting a decoding mode, out of a plurality of decoding modes, based on the stability value D(m); and applying the selected decoding mode.

## Claims

### Claim 1

A method for decoding an audio signal, the method comprising:
determining a stability value D(m) based on a difference, in a transform domain, between a range of a spectral envelope of a frame m and a corresponding range of a spectral envelope of an adjacent frame m−1, each range comprising a set of quantized spectral envelope values related to the energy in spectral bands of a segment of the audio signal;
selecting a decoding mode out of a plurality of decoding modes based on the stability value D(m); and
applying the selected decoding mode.

### Claim 2 (depends on 1)

Method according to claim 1, further comprising:
low pass filtering the stability value D(m), thus achieving a filtered stability value {tilde over (D)}(m);
mapping the filtered stability value {tilde over (D)}(m) to a scalar range of [0,1] by use of a sigmoid function, thus achieving a stability parameter S(m);
and wherein the selecting of a decoding mode is based on the stability parameter S(m).

### Claim 3 (depends on 1)

The method according to claim 1, wherein the selecting of a decoding mode comprises determining whether the segment of the audio signal represented in frame m comprises speech or music.

### Claim 4 (depends on 1)

The method according to claim 1, wherein at least one decoding mode out of the plurality of decoding modes is more suitable for speech than for music, and at least one decoding mode is more suitable for music than for speech.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the selection of a decoding mode out of a plurality of decoding modes is related to error concealment.

### Claim 6 (depends on 1)

The method according to claim 1, wherein the selection of a decoding mode is further based on a Markov model defining state transition probabilities related to transitions between speech and music in the audio signal.

### Claim 7 (depends on 1)

The method according to claim 1, wherein the selection of a decoding mode is further based on a transient measure, indicating the transient structure of the spectral contents of frame m.

### Claim 8 (depends on 1)

A non-transitory computer readable storage medium storing a computer program, comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to claim 1.

### Claim 9

A decoder for decoding an audio signal, the decoder being configured to:
determine a stability value D(m) based on a difference, in a transform domain, between a range of a spectral envelope of a frame m and a corresponding range of a spectral envelope of an adjacent frame m−1, each range comprising a set of quantized spectral envelope values related to the energy in spectral bands of a segment of the audio signal;
select a decoding mode out of a plurality of decoding modes based on the stability value D(m); and to
apply the selected decoding mode.

### Claim 10 (depends on 9)

The decoder according to claim 9, being further configured to:
low pass filter the stability value D(m), thus achieving a filtered stability value {tilde over (D)}(m); and to
map the filtered stability value {tilde over (D)}(m) to a scalar range of [0,1] by use of a sigmoid function, thus achieving a stability parameter S(m);
and wherein the selecting of a decoding mode is based on the stability parameter S(m).

### Claim 11 (depends on 9)

The decoder according to claim 9, wherein the selecting of a decoding mode is configured to comprise determining whether the segment of the audio signal represented in frame m comprises speech or music.

### Claim 12 (depends on 9)

The decoder according to claim 9, wherein the selection of a decoding mode out of a plurality of decoding modes is related to error concealment.

### Claim 13 (depends on 9)

The decoder according to claim 9, wherein the selecting of a decoding mode is configured to be based on a Markov model defining state transition probabilities related to transitions between speech and music in the audio signal.

### Claim 14 (depends on 9)

The decoder according to claim 9, being configured to further base the selection of a decoding mode on a transient measure, indicating the transient structure of the spectral contents of frame m.

### Claim 15 (depends on 9)

Host device comprising a decoder according to claim 9.