# US 12,112,765 B2 · Audio encoder, audio decoder, method for encoding an audio signal and method for decoding an encoded audio signal

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- Number: US 12,112,765 B2
- Document ID: US12112765B2
- Status: Granted
- Kind: B2
- Application number: 16/802,397
- Filed: 2020-02-26
- Published: 2020-07-16
- Granted: 2024-10-08
- Earliest claimed: 2015-03-09
- Assignees: Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.
- Applicants: Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.
- Inventors: Bernd Edler; Christian Helmrich; Max Neuendorf; Benjamin Schubert
- Web page: https://patentgrep.com/patent/US12112765B2

## CPC

- G10L 19/032: Quantisation or dequantisation of spectral components
- G10L 19/02: using spectral analysis, e.g. transform vocoders or subband vocoders
- H04N 19/547: Motion estimation performed in a transform domain
- H04N 19/635: characterised by filter definition or implementation details
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

An encoder for encoding an audio signal is configured to encode the audio signal in a transform domain or filter-bank domain, is configured to determine spectral coefficients of the audio signal for a current frame and at least one previous frame, and is configured to selectively apply predictive encoding to a plurality of individual spectral coefficients or groups of spectral coefficients which are separated by at least one spectral coefficient.

## Claims

### Claim 1

An encoder for encoding an audio signal, wherein the encoder comprises a processor operable to execute computer program instructions and a memory operable to store computer program instructions executable by the processor, for performing the steps of
encoding the audio signal in a transform domain or filter-bank domain,
determining spectral coefficients of the audio signal for a current frame and at least one previous frame,
determining a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics,
selectively applying predictive encoding to a plurality of individual spectral coefficients or groups of spectral coefficients based on the spacing value,
selecting the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied based on the spacing value,
wherein the spacing value indicates those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal.

### Claim 2 (depends on 1)

The encoder according to claim 1, wherein the plurality of individual spectral coefficients or groups of spectral coefficients are separated by at least one spectral coefficient.

### Claim 3 (depends on 2)

The encoder according to claim 2, wherein the predictive encoding is not applied to the at least one spectral coefficient by which the individual spectral coefficients or the groups of spectral coefficients are separated.

### Claim 4 (depends on 1)

The encoder according to claim 1, comprising the processor and the memory for performing the step of
encoding the plurality of individual spectral coefficients or the groups of spectral coefficients of the current frame, by coding prediction errors between a plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients of the current frame and the plurality of individual spectral coefficients or groups of spectral coefficients of the current frame.

### Claim 5 (depends on 4)

The encoder according to claim 4, comprising the processor and the memory for performing the steps of
deriving prediction coefficients from the spacing value, and
calculating the plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients for the current frame using a corresponding plurality of individual spectral coefficients or corresponding groups of spectral coefficients of at least two previous frames and using the derived prediction coefficients.

### Claim 6 (depends on 5)

The encoder according to claim 5, comprising the processor and the memory for performing the step of
providing an encoded audio signal, the encoded audio signal not comprising the prediction coefficients or encoded versions thereof.

### Claim 7 (depends on 4)

The encoder according to claim 4, comprising the processor and the memory for performing the step of
determining the plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients for the current frame using corresponding quantized versions of the plurality of individual spectral coefficients or the groups of spectral coefficients of the previous frame.

### Claim 8 (depends on 7)

The encoder according to claim 7, comprising the processor and the memory for performing the steps of
deriving prediction coefficients from the spacing value, and
calculating the plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients for the current frame using corresponding quantized versions of the plurality of individual spectral coefficients or the groups of spectral coefficients of at least two previous frames and using the derived prediction coefficients.

### Claim 9 (depends on 4)

The encoder according to claim 4, comprising the processor and the memory for performing the step of
providing an encoded audio signal, the encoded audio signal comprising quantized versions of the prediction errors instead of quantized versions of the plurality of individual spectral coefficients or of the groups of spectral coefficients for the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied.

### Claim 10 (depends on 9)

The encoder according to claim 9, wherein the encoded audio signal comprises quantized versions of the spectral coefficients to which predictive encoding is not applied, such that there is an alternation of spectral coefficients or groups of spectral coefficients for which quantized versions of the prediction errors are comprised in the encoded audio signal and spectral coefficients or groups of spectral coefficients for which quantized versions are provided without using predictive encoding.

### Claim 11 (depends on 1)

The encoder according to claim 1, comprising the processor and the memory for performing the steps of
determining an instantaneous fundamental frequency of the audio signal and deriving the spacing value from the instantaneous fundamental frequency or a fraction or a multiple thereof.

### Claim 12 (depends on 1)

The encoder according to claim 1, comprising the processor and the memory for performing the step of
selecting individual spectral coefficients or groups of spectral coefficients spectrally arranged according to a harmonic grid defined by the spacing value for a predictive encoding.

### Claim 13 (depends on 1)

The encoder according to claim 1, comprising the processor and the memory for performing the step of
selecting spectral coefficients, spectral indices of which are equal to or lie within a range around a plurality of spectral indices derived on the basis of the spacing value, for a predictive encoding.

### Claim 14 (depends on 13)

The encoder according to claim 13, comprising the processor and the memory for performing the step of
setting a width of the range in dependence on the spacing value.

### Claim 15 (depends on 1)

The encoder according to claim 1, comprising the processor and the memory for performing the step of
selecting the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied such that there is a periodic alternation, periodic with a tolerance of +/−1 spectral coefficient, between the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied and the spectral coefficients or groups of spectral coefficients to which predictive encoding is not applied.

### Claim 16 (depends on 1)

The encoder according to claim 1, wherein the audio signal comprises at least two harmonic signal components, the encoder comprising the processor and the memory for performing the step of
selectively applying predictive encoding to those plurality of individual spectral coefficients or groups of spectral coefficients which represent the at least two harmonic signal components or spectral environments around the at least two harmonic signal components of the audio signal.

### Claim 17 (depends on 16)

The encoder according to claim 16, comprising the processor and the memory for performing the step of
not applying predictive encoding to those plurality of individual spectral coefficients or groups of spectral coefficients which do not represent the at least two harmonic signal components or spectral environments of the at least two harmonic signal components of the audio signal.

### Claim 18 (depends on 16)

The encoder according to claim 16, comprising the processor and the memory for performing the step of
not applying predictive encoding to those plurality of individual spectral coefficients or groups of spectral coefficients which belong to a non-tonal background noise between signal harmonics.

### Claim 19 (depends on 16)

The encoder according to claim 16, wherein the spacing value is a harmonic spacing value indicating a spectral spacing between the at least two harmonic signal components of the audio signal, the harmonic spacing value indicating those plurality of individual spectral coefficients or groups of spectral coefficients which represent the at least two harmonic signal components of the audio signal.

### Claim 20 (depends on 1)

The encoder according to claim 1, comprising the processor and the memory for performing the step of
providing an encoded audio signal,
including in the encoded audio signal the spacing value or an encoded version thereof.

### Claim 21 (depends on 1)

The encoder according to claim 1, wherein the spectral coefficients are spectral bins.

### Claim 22

A decoder for decoding an encoded audio signal to produce a decoded audio signal, wherein the decoder comprises a processor operable to execute computer program instructions and a memory operable to store computer program instructions executable by the processor, for performing the steps of:
decoding the encoded audio signal in a transform domain or filter-bank domain,
acquiring a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics,
parsing the encoded audio signal to acquire encoded spectral coefficients of the audio signal for a current frame and at least one previous frame, and wherein the decoder is configured to selectively apply predictive decoding to a plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients based on the spacing value,
selecting the plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients to which predictive decoding is applied based on the spacing value,
wherein the spacing value indicates those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal.

### Claim 23 (depends on 22)

The decoder according to claim 22, wherein the plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients are separated by at least one encoded spectral coefficient.

### Claim 24 (depends on 23)

The decoder according to claim 23, wherein the predictive decoding is not applied to the at least one spectral coefficient by which the individual spectral coefficients or the group of spectral coefficients are separated.

### Claim 25 (depends on 22)

The decoder according to claim 22, comprising the processor and the memory for performing the steps of
entropy decoding the encoded spectral coefficients, to acquire quantized prediction errors for the spectral coefficients to which predictive decoding is to be applied and quantized spectral coefficients for spectral coefficients to which predictive decoding is not to be applied; and
applying the quantized prediction errors to a plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients, to acquire, for the current frame, decoded spectral coefficients associated with the encoded spectral coefficients to which predictive decoding is applied.

### Claim 26 (depends on 25)

The decoder according to claim 25, comprising the processor and the memory for performing the step of
determining the plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients for the current frame based on a corresponding plurality of the individual encoded spectral coefficients or groups of encoded spectral coefficients of the previous frame.

### Claim 27 (depends on 26)

The decoder according to claim 26, comprising the processor and the memory for performing the steps of
deriving prediction coefficients from the spacing value,
calculating the plurality of predicted individual spectral coefficients or groups of predicted spectral coefficients for the current frame using a corresponding plurality of previously decoded individual spectral coefficients or groups of previously decoded spectral coefficients of at least two previous frames and using the derived prediction coefficients.

### Claim 28 (depends on 23)

The decoder according to claim 23, comprising the processor and the memory for performing the step of
decoding the encoded audio signal in order to acquire quantized prediction errors instead of a plurality of individual quantized spectral coefficients or groups of quantized spectral coefficients for the plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients to which predictive decoding is applied.

### Claim 29 (depends on 28)

The decoder according to claim 28, comprising the processor and the memory for performing the step of
decoding the encoded audio signal in order to acquire quantized spectral coefficients for encoded spectral coefficients to which predictive decoding is not applied, such that there is an alternation of encoded spectral coefficients or groups of encoded spectral coefficients for which quantized prediction errors are acquired and encoded spectral coefficients or groups of encoded spectral coefficients for which quantized spectral coefficients are acquired.

### Claim 30 (depends on 22)

The decoder according to claim 22, comprising the processor and the memory for performing the step of
selecting individual spectral coefficients or groups of spectral coefficients spectrally arranged according to a harmonic grid defined by the spacing value for a predictive decoding.

### Claim 31 (depends on 22)

The decoder according to claim 22, comprising the processor and the memory for performing the step of
selecting spectral coefficients, spectral indices of which are equal to or lie within a range around a plurality of spectral indices derived on the basis of the spacing value, for a predictive decoding.

### Claim 32 (depends on 31)

The decoder according to claim 31, comprising the processor and the memory for performing the step of
setting a width of the range in dependence on the spacing value.

### Claim 33 (depends on 22)

The decoder according to claim 22, wherein the encoded audio signal comprises the spacing value or an encoded version thereof, the decoder comprising the processor and the memory for performing the step of
extracting the spacing value or the encoded version thereof from the encoded audio signal to acquire the spacing value.

### Claim 34 (depends on 22)

The decoder according to claim 22, comprising the processor and the memory for performing the step of
determining the spacing value.

### Claim 35 (depends on 34)

The decoder according to claim 34, comprising the processor and the memory for performing the steps of
determining an instantaneous fundamental frequency and deriving the spacing value from the instantaneous fundamental frequency or a fraction or a multiple thereof.

### Claim 36 (depends on 22)

The decoder according to claim 22, comprising the processor and the memory for performing the step of
selecting the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive decoding is applied such that there is a periodic alternation, periodic with a tolerance of +/−1 spectral coefficients, between the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive decoding is applied and the spectral coefficients to which predictive decoding is not applied.

### Claim 37 (depends on 23)

The decoder according to claim 23, wherein the audio signal represented by the encoded audio signal comprises at least two harmonic signal components, the decoder comprising the processor and the memory for performing the step of
applying predictive decoding to those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent the at least two harmonic signal components or spectral environments around the at least two harmonic signal components of the audio signal.

### Claim 38 (depends on 37)

The decoder according to claim 37, comprising the processor and the memory for performing the steps of
identifying the at least two harmonic signal components, and selectively applying predictive decoding to those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which are associated with the identified harmonic signal components.

### Claim 39 (depends on 37)

The decoder according to claim 37, wherein the encoded audio signal comprises the spacing value or an encoded version thereof, wherein the spacing value identifies the at least two harmonic signal components, the decoder comprising the processor and the memory for performing the step of
applying predictive decoding to those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which are associated with the identified harmonic signal components.

### Claim 40 (depends on 37)

The decoder according to claim 37, comprising the processor and the memory for performing the step of
not applying predictive decoding to those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which do not represent the at least two harmonic signal components or spectral environments of the at least two harmonic signal components of the audio signal.

### Claim 41 (depends on 37)

The decoder according to claim 37, comprising the processor and the memory for performing the step of
not applying predictive decoding to those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which belong to a non-tonal background noise between signal harmonics of the audio signal.

### Claim 42 (depends on 22)

The decoder according to claim 22, wherein the encoded audio signal comprises the spacing value or an encoded version thereof, wherein the spacing value is a harmonic spacing value, the harmonic spacing value indicating those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal.

### Claim 43 (depends on 22)

The decoder according to claim 22, wherein the spectral coefficients are spectral bins.

### Claim 44

Method for encoding an audio signal in a transform domain or filter-bank domain using an encoder comprising a processor operable to execute computer program instructions and a memory operable to store computer program instructions executable by the processor, the method comprising:
determining spectral coefficients of the audio signal for a current frame and at least one previous frame;
determining a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics; and
selectively applying predictive encoding to a plurality of individual spectral coefficients or groups of spectral coefficients based on the spacing value, wherein the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied are selected based on the spacing value,
wherein the spacing value indicates those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal.

### Claim 45

Method for decoding an encoded audio signal in a transform domain or filter-bank domain to produce a decoded audio signal, using a decoder comprising a processor operable to execute computer program instructions and a memory operable to store computer program instructions executable by the processor, the method comprising:
parsing the encoded audio signal to acquire encoded spectral coefficients of the audio signal for a current frame and at least one previous frame;
acquiring a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics; and
selectively applying predictive decoding to a plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients based on the spacing value, wherein the plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients to which predictive decoding is applied are selected based on the spacing value,
wherein the spacing value indicates those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal.

### Claim 46

A non-transitory digital storage medium having a computer program stored thereon to perform the method for encoding an audio signal in a transform domain or filter-bank domain, the method comprising:
determining spectral coefficients of the audio signal for a current frame and at least one previous frame;
determining a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics; and
selectively applying predictive encoding to a plurality of individual spectral coefficients or groups of spectral coefficients based on the spacing value, wherein the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied are selected based on the spacing value,
wherein the spacing value indicates those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal
when said computer program is run by a computer.

### Claim 47

A non-transitory digital storage medium having a computer program stored thereon to perform the method for decoding an encoded audio signal in a transform domain or filter-bank domain to produce a decoded audio signal, the method comprising:
parsing the encoded audio signal to acquire encoded spectral coefficients of the audio signal for a current frame and at least one previous frame;
acquiring a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics; and
selectively applying predictive decoding to a plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients based on the spacing value, wherein the plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients to which predictive decoding is applied are selected based on the spacing value,
wherein the spacing value indicates those plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients which represent at least two harmonic signal components of the audio signal when said computer program is run by a computer.

### Claim 48

An encoder for encoding an audio signal, wherein the encoder comprises a processor operable to execute computer program instructions and a memory operable to store computer program instructions executable by the processor, for performing the steps of
encoding the audio signal in a transform domain or filter-bank domain,
determining spectral coefficients of the audio signal for a current frame and at least one previous frame,
determining a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics,
selectively applying predictive encoding to a plurality of individual spectral coefficients or groups of spectral coefficients based on the spacing value,
selecting the plurality of individual spectral coefficients or groups of spectral coefficients to which predictive encoding is applied based on the spacing value;
selecting individual spectral coefficients or groups of spectral coefficients spectrally arranged according to a harmonic grid defined by the spacing value for a predictive encoding.

### Claim 49

A decoder for decoding an encoded audio signal to produce a decoded audio signal, wherein the decoder comprises a processor operable to execute computer program instructions and a memory operable to store computer program instructions executable by the processor, for performing the steps of:
decoding the encoded audio signal in a transform domain or filter-bank domain;
acquiring a spacing value, wherein the spacing value is a harmonic spacing value describing a spacing between harmonics;
parsing the encoded audio signal to acquire encoded spectral coefficients of the audio signal for a current frame and at least one previous frame;
selectively applying predictive decoding to a plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients based on the spacing value;
selecting the plurality of individual encoded spectral coefficients or groups of encoded spectral coefficients to which predictive decoding is applied based on the spacing value;
selecting individual spectral coefficients or groups of spectral coefficients spectrally arranged according to a harmonic grid defined by the spacing value for a predictive decoding.