# US 10,770,081 B2 · Stereo audio signal encoder

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- Number: US 10,770,081 B2
- Document ID: US10770081B2
- Status: Granted
- Kind: B2
- Application number: 16/479,916
- Filed: 2018-01-03
- Published: 2019-12-26
- Granted: 2020-09-08
- Earliest claimed: 2017-01-31
- Assignees: Nokia Technologies Oy
- Applicants: Nokia Technologies Oy
- Inventors: Adriana Vasilache
- Web page: https://patentgrep.com/patent/US10770081B2

## CPC

- G10L 19/008: Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
- G10L 19/035: Scalar quantisation
- G10L 19/24: Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
- H03M 7/4075: {Golomb codes}
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- H03M: CODING; DECODING; CODE CONVERSION IN GENERAL (using fluidic means F15C4/00; optical analogue/digital converters G02F7/00; coding, decoding or code conversion, specially adapted for particular applications, see the relevant subclasses, e.g. G01D, G01R, G06F, G06T, G09G, G10L, G11B, G11C, H04B, H04L, H04M, H04N; ciphering or deciphering for cryptography or other purposes involving the need for secrecy G09C)

## Abstract

A method comprising: receiving at least two audio channel signals; determining, for a first frame, at least two parameters representing a difference between the at least two channel audio signals; scalar quantising the at least two parameters to generate at least two index values; adaptively encoding an initial scalar quantized parameter of the at least two parameters; determining whether the initial scalar quantized parameter has a value different from a predetermined value; adaptively encoding any unencoded scalar quantized parameters where the initial scalar quantized parameter has a value different from the predetermined value; determining whether all of the at least two scalar quantized parameters have values equal to the predetermined value where the initial scalar quantized parameter has a value equal to the predetermined value; adaptively encoding any unencoded scalar quantized parameters and generating an indicator that an output is one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and at least one of the at least two scalar quantized parameters have values different from the predetermined value; generating an indicator that the output is the other of the one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and all of the at least two scalar quantized parameters have values equal to the predetermined value; generating a single channel representation of the at least two audio channel signals dependent on the at least two parameters; and encoding the single channel representation.

## Claims

### Claim 1

A method comprising:
receiving at least two audio channel signals;
determining, for a first frame, at least two parameters representing a difference between the at least two channel audio signals;
scalar quantising the at least two parameters to generate at least two index values;
adaptively encoding an initial scalar quantized parameter of the at least two parameters;
determining whether the initial scalar quantized parameter has a value different from a predetermined value;
adaptively encoding any unencoded scalar quantized parameters where the initial scalar quantized parameter has a value different from the predetermined value;
determining whether the at least two scalar quantized parameters have values equal to the predetermined value where the initial scalar quantized parameter has a value equal to the predetermined value;
adaptively encoding any unencoded scalar quantized parameters and generating an indicator that an output is one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and at least one of the at least two scalar quantized parameters have values different from the predetermined value;
generating an indicator that the output is the other of the one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and the at least two scalar quantized parameters have values equal to the predetermined value;
generating a single channel representation of the at least two audio channel signals dependent on the at least two parameters; and
encoding the single channel representation.

### Claim 2 (depends on 1)

The method as claimed in claim 1, wherein adaptively encoding the initial scalar quantized parameter and adaptively encoding the any unencoded scalar quantized parameters comprises:
determining an initial index map for reordering an index value associated with the scalar quantized parameter, and determining at least one further index map for reordering at least one further index value associated with the any unencoded scalar quantized parameters, wherein the at least one further index map is determined based on the index value associated with the scalar quantized parameter;
reordering the index value associated with the scalar quantized parameter based on the initial index map;
reordering the at least one further index value associated with the any unencoded scalar quantized parameters based on the at least one further index map;
encoding the reordered index value associated with the scalar quantized parameter dependent on an order position of the reordered index value associated with the scalar quantized parameter; and
encoding the at least one further index value associated with the any unencoded scalar quantized parameters based on an order position of the reordered at least one further index value associated with the any unencoded scalar quantized parameters.

### Claim 3 (depends on 1)

The method as claimed in claim 1, wherein adaptively encoding the scalar quantized parameters comprises:
determining an occurrence frequency of index values;
reordering the index value dependent on the occurrence frequency of index values to generate a reordered index value; and
encoding the reordered index value dependent on an order position of the reordered index value.

### Claim 4

A method comprising:
decoding from a first part of a signal at least one parameter index value, wherein the parameter index value represents a difference between at least two channel audio signals, and from a second part of the signal a fixed rate/variable rate indicator and wherein the signal is an encoded multichannel audio signal;
reordering a first of the at least one parameter index value based on a first determined reordering to generate a first reordered index value;
determining whether a parameter value associated with the first reordered index is different from a predetermined value;
adaptively reordering any further of the at least one parameter index values where the parameter value associated with the first reordered index is different to the predetermined value;
determining whether the fixed rate/variable rate indicator is a determined one of a fixed rate/variable rate value;
adaptively reordering any further of the at least one parameter index value where the parameter value associated with the first reordered index is equal to the predetermined value and the fixed rate/variable rate indicator is the determined one of a fixed rate/variable rate value; and
duplicating the at least one parameter index value for a frame where the parameter value associated with the first reordered index is equal to the predetermined value and the fixed rate/variable rate indicator is other than the determined one of a fixed rate/variable rate value.

### Claim 5 (depends on 4)

The method as claimed in claim 4, wherein reordering the first of the at least one parameter index value based on a first determined reordering to generate a first reordered index value comprises reordering a first parameter index value based on a first determined reordering to generate a first reordered index value, and adaptively reordering any further of the at least one parameter index values comprises reordering any further index values based on a second determined reordering to generate a second reordered index value, wherein the second determined reordering is based on the first reordered index value.

### Claim 6

An apparatus comprising:
a parameter determiner configured to determine, for a first frame, at least two parameters representing a difference between the at least two channel audio signals;
a scalar quantiser configured to scalar quantile the at least two parameters to generate at least two index values;
a parameter encoder configured to adaptively encode an initial scalar quantiser parameter of the at least two parameters;
a bitstream indicator configured to generate an indicator that an output bitstream is one or other of fixed or variable rate coding;
a encoder controller configured to determine whether the initial scalar quantiser parameter has a value different from a predetermined value, and configured to control the parameter encoder to adaptively encode any unencoded scalar quantized parameters where the initial scalar quantized parameter has a different from the predetermined value, and wherein
the encoder controller is further configured to determine whether the at least two scalar quantized parameters have values equal to the predetermined value where the initial scalar quantized parameter has a value equal to the predetermined value, the encoder controller further configured to:
control the parameter encoder to adaptively encode any unencoded scalar quantized parameters and control the bitstream indicator to generate the indicator that the output bitstream is one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and at least one of the at least two scalar quantized parameters have values different from the predetermined value;
control the bitstream indicator to generate an indicator that the output is the other of the one of fixed or variable rate coding where the initial scalar quantized parameter has a value equal to the predetermined value and the at least two scalar quantized parameters have values equal to the predetermined value;
a mono channel generator configured to generate a single channel representation of the at least two audio channel signals dependent on the at least two parameters; and
a mono channel encoder configured to encode the single channel representation.

### Claim 7 (depends on 6)

The apparatus as claimed in claim 6, wherein the parameter encoder is configured to:
determine an initial index map for reordering an index value associated with the scalar quantized parameter, and determining at least one further index map for reordering at least one further index value associated with the any unencoded scalar quantized parameters, wherein the at least one further index map is determined based on the index value associated with the scalar quantized parameter;
reorder the index value associated with the scalar quantized parameter based on the initial index map;
reorder the at least one further index value associated with the any unencoded scalar quantized parameters based on the at least one further index map;
encode the reordered index value associated with the scalar quantized parameter dependent on an order position of the reordered index value associated with the scalar quantized parameter; and
encode the at least one further index value associated with the any unencoded scalar quantized parameters based on an order position of the reordered at least one further index value associated with the any unencoded scalar quantized parameters.

### Claim 8 (depends on 6)

The apparatus as claimed in claim 6, wherein the parameter encoder is configured to:
determine an occurrence frequency of index values;
reorder the index value dependent on the occurrence frequency of index values to generate a reordered index value; and
encode the reordered index value dependent on an order position of the reordered index value.

### Claim 9 (depends on 7)

The apparatus as claimed in claim 7, wherein the parameter encoder is configured to apply a Golomb-Rice encoding to the reordered index value dependent on an order position of the reordered index value.

### Claim 10 (depends on 6)

The apparatus as claimed in claim 6, wherein the scalar quantiser is configured to order the scalar quantized output according to a predetermined map.

### Claim 11 (depends on 6)

The apparatus as claimed in claim 6, wherein the one of fixed or variable rate coding is the fixed rate coding and the other of fixed or variable rate coding is variable rate coding.

### Claim 12 (depends on 6)

The apparatus as claimed in claim 6, wherein the mono channel encoder is configured to:
determine a number of bits used for encoding the at least two scalar quantized parameters; and
encode the single channel representation based on the determined number of bits.

### Claim 13

An apparatus for decoding comprising:
a parameter decoder configured to decode from a first part of a signal at least one parameter index value, wherein the parameter index value represents a difference between at least two channel audio signals; and wherein the signal is an encoded multichannel audio signal
an indicator decoder configured to decode from a second part of the signal a fixed rate/variable rate indicator;
a parameter reorderer configured to reorder a first of the at least one parameter index value based on a first determined reordering to generate a first reordered index value;
a parameter determiner configured to determine whether a parameter value associated with the first reordered index is different from a predetermined value;
the parameter determiner is further configured to adaptively reordering any further of the at least one parameter index values where the parameter value associated with the first reordered index is different to the predetermined value;
the parameter determiner further configured to determine whether the fixed rate/variable rate indicator is a determined one of a fixed rate/variable rate value;
the parameter reorderer configured to adaptively reorder any further of the at least one parameter index value where the parameter value associated with the first reordered index is equal to the predetermined value and the fixed rate/variable rate indicator is the determined one of a fixed rate/variable rate value, and duplicate the at least one parameter index value for a frame where the parameter value associated with the first reordered index is equal to the predetermined value and the fixed rate/variable rate indicator is other than the determined one of a fixed rate/variable rate value.

### Claim 14 (depends on 13)

The apparatus as claimed in claim 13, wherein the parameter reorderer is configured to reorder the first parameter index value based on a first determined reordering to generate a first reordered index value and reorder any further index values based on a second determined reordering to generate a second reordered index value, wherein the second determined reordering is based on the first reordered index value.

### Claim 15 (depends on 13)

The apparatus as claimed in claim 13, wherein the parameter reorderer configured to adaptively reorder any further of the at least one parameter index values is configured to:
determine an occurrence frequency of index values;
reorder the index value to generate a reordered index value, wherein the reordering is dependent on the occurrence frequency of reordered index values.

### Claim 16 (depends on 13)

The apparatus as claimed in claim 13, wherein the parameter reorderer is further configured to dequantize the reordered index values to generate the parameter.

### Claim 17 (depends on 13)

The apparatus as claimed in claim 13, wherein the parameter decoder is configured to decode the first part of a signal using a Golomb-Rice decoding.

### Claim 18 (depends on 13)

The apparatus as claimed in claim 13, wherein the determined one of a fixed rate/variable rate value is a fixed rate coding indicator value.

### Claim 19 (depends on 13)

The apparatus as claimed in claim 13, further comprising a further decoder configured to:
receive from a further part of a signal an encoded downmix channel signal;
determine a number of bits used in the first part of the signal; and
decode the encoded downmix channel signal based on the number of bits used in the first part of the signal.

### Claim 20 (depends on 13)

The apparatus as claimed in claim 13, wherein the predetermined value is zero.