ETSI TS 103 634 V1.3.1 (2021-10)

Digital Enhanced Cordless Telecommunications (DECT); Low Complexity Communication Codec plus (LC3plus)

RTS/DECT-00369

General Information

• Status: Not Published
• Technical Committee: DECT - Digital Enhanced Cordless Telecommunications (DECT)
• Current Stage: 12 - Completion
• Due Date: 25-Oct-2021
• Completion Date: 18-Oct-2021

Standards Content (Sample)

ETSI TS 103 634 V1.3.1 (2021-10)






TECHNICAL SPECIFICATION
Digital Enhanced Cordless Telecommunications (DECT);
Low Complexity Communication Codec plus (LC3plus)

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2 ETSI TS 103 634 V1.3.1 (2021-10)

Reference
RTS/DECT-00369
Keywords
audio, codec, DECT, full-band, LC3plus,
superwideband, voice, VoIP

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© ETSI 2021.
All rights reserved.

ETSI

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3 ETSI TS 103 634 V1.3.1 (2021-10)
Contents
Intellectual Property Rights . 9
Foreword . 9
Modal verbs terminology . 9
Executive summary . 10
Introduction . 10
1 Scope . 11
2 References . 11
2.1 Normative references . 11
2.2 Informative references . 12
3 Definition of terms, symbols and abbreviations . 13
3.1 Terms . 13
3.2 Symbols . 14
3.2.1 Mathematical symbols . 14
3.2.2 Operator symbols . 14
3.3 Abbreviations . 14
4 General description. 16
4.1 Overview . 16
4.2 Transcoding functions . 17
4.3 ANSI C-code . 19
4.4 Conformance testing. 19
4.5 RTP payload format . 19
4.6 Performance characterization . 19
5 Codec algorithm description . 20
5.1 General codec description . 20
5.2 General codec parameters. 21
5.2.1 Audio channels . 21
5.2.2 Sampling rates . 21
5.2.3 Bits per sample . 21
5.2.4 Frame size and delay. 21
5.2.5 Bit budget and bitrate . 22
5.2.6 Bandwidth . 22
5.3 Encoding process . 22
5.3.1 Encoder modules . 22
5.3.2 Input signal . 23
5.3.3 Input signal scaling . 23
5.3.4 Low delay MDCT analysis . 23
5.3.4.1 Overview . 23
5.3.4.2 Update time buffer . 24
5.3.4.3 Time-frequency transformation. 24
5.3.4.4 Energy estimation per band . 25
5.3.4a Near Nyquist detector . 25
5.3.5 Bandwidth detector . 26
5.3.5.1 Algorithm . 26
5.3.5.2 Parameters . 27
5.3.6 Time Domain Attack Detector . 27
5.3.6.1 Overview . 27
5.3.6.2 Downsampling and Filtering of Input Signal . 27
5.3.6.3 Energy Calculation . 27
5.3.6.4 Attack Detection . 28
5.3.7 Spectral Noise Shaping . 28
5.3.7.1 Overview . 28
5.3.7.2 SNS analysis . 29
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4 ETSI TS 103 634 V1.3.1 (2021-10)
5.3.7.2.1 Overview . 29
5.3.7.2.2 Padding . 29
5.3.7.2.3 Smoothing . 29
5.3.7.2.4 Pre-emphasis . 29
5.3.7.2.5 Noise floor . 30
5.3.7.2.6 Logarithm . 30
5.3.7.2.7 Band Energy Grouping . 30
5.3.7.2.8 Mean removal and scaling, attack handling. 30
5.3.7.3 SNS quantization . 31
5.3.7.3.1 General . 31
5.3.7.3.2 Stage 1 . 31
5.3.7.3.3 Stage 2 . 32
5.3.7.3.4 Multiplexing of SNS VQ Codewords . 37
5.3.7.3.5 Synthesis of the Quantized SNS scale factor vector . 39
5.3.7.4 SNS scale factors interpolation . 39
5.3.7.5 Spectral shaping . 39
5.3.8 Bandwidth control . 40
5.3.9 Temporal Noise Shaping (TNS) . 40
5.3.9.1 Overview . 40
5.3.9.2 TNS analysis . 41
5.3.9.3 Quantization . 42
5.3.9.4 Filtering . 43
5.3.10 Long term postfilter . 43
5.3.10.1 Overview . 43
5.3.10.2 Time-domain signals . 43
5.3.10.3 Resampling. 44
5.3.10.4 High-pass filtering . 44
5.3.10.5 Pitch detection algorithm . 44
5.3.10.6 LTPF bitstream . 45
5.3.10.7 LTPF pitch-lag parameter . 46
5.3.10.8 LTPF activation bit . 47
5.3.11 Spectral quantization. 47
5.3.11.1 Overview . 47
5.3.11.2 Bit budget . 48
5.3.11.3 First global gain estimation . 48
5.3.11.4 Quantization . 49
5.3.11.5 Bit consumption . 49
5.3.11.6 Truncation . 51
5.3.11.7 Global gain adjustment . 51
5.3.12 Residual coding . 52
5.3.13 Noise level estimation . 52
5.3.13.1 Overview . 52
5.3.13.2 Relevant spectral lines . 53
5.3.13.3 Noise level calculation . 53
5.3.14 Bitstream encoding . 54
5.3.14.1 Overview . 54
5.3.14.2 Initialization . 54
5.3.14.3 Side information . 54
5.3.14.4 Arithmetic encoding . 55
5.3.14.4.1 Overview . 55
5.3.14.4.2 Pseudo code implementation . 56
5.3.14.5 Residual data and finalization . 57
5.3.14.6 Functions . 57
5.3.15 Encoding of Low-frequency effects . 59
5.4 Decoding process . 60
5.4.1 Decoder modules . 60
5.4.2 Bitstream decoding . 60
5.4.2.1 Overview . 60
5.4.2.2 Initialization . 60
5.4.2.3 Side information . 61
5.4.2.4 Special decoder mode indicators . 61
5.4.2.5 Padding pattern . 62
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5 ETSI TS 103 634 V1.3.1 (2021-10)
5.4.2.6 Bandwidth interpretation . 62
5.4.2.7 Arithmetic decoding . 63
5.4.2.8 Residual data and finalization . 64
5.4.2.9 Functions . 66
5.4.3 Residual decoding . 67
5.4.4 Noise filling . 67
5.4.5 Global gain. 68
5.4.6 TNS decoder . 68
5.4.7 SNS decoder . 69
5.4.7.1 Overview . 69
5.4.7.2 SNS scale factor decoding . 69
5.4.7.2.1 SNS VQ decoding . 69
5.4.7.2.2 Stage 1 SNS VQ decoding. 69
5.4.7.2.3 Stage 2 SNS VQ decoding. 70
5.4.7.2.4 Unit energy normalization of the received shape . 73
5.4.7.2.5 Reconstruction of the Quantized SNS Scalefactors . 73
5.4.7.3 SNS scale factors interpolation . 73
5.4.7.4 Spectral Shaping . 74
5.4.8 Low delay MDCT synthesis . 74
5.4.9 Long term postfilter . 74
5.4.9.1 Overview . 74
5.4.9.2 Transition handling . 75
5.4.9.3 Remaining of the frame . 76
5.4.10 Output signal scaling and rounding . 77
5.5 Frame structure . 78
5.6 Error concealment . 78
5.6.1 General consideration . 78
5.6.2 PLC trigger . 79
5.6.3 PLC method selection and method application . 79
5.6.3.1 Method selection . 79
5.6.3.2 MDCT frame repetition with sign scrambling . 80
5.6.3.3 Time domain concealment . 82
5.6.3.3.1 Overview . 82
5.6.3.3.2 LPC parameter calculation . 82
5.6.3.3.3 Construction of the periodic part of the excitation . 83
5.6.3.3.4 Construction of the random part of the excitation . 85
5.6.3.3.5 Construction of the total excitation, synthesis and post-processing . 86
5.6.3.3.6 Time domain alias cancelation . 86
5.6.3.3.7 Handling of multiple frame losses . 87
5.6.3.4 Frequency domain concealment (Phase ECU) . 87
5.6.3.4.1 Phase ECU overview . 87
5.6.3.4.2 Spectral Shape . 88
5.6.3.4.3 Transient analysis . 89
5.6.3.4.4 Fine Spectral analysis . 90
5.6.3.4.5 Frame reconstruction . 91
5.6.4 PLC operation related to LTPF . 92
5.7 External rate adaptation . 93
5.8 High-resolution audio support . 93
5.8.1 Overview . 93
5.8.2 Changes to the algorithm in high-resolution mode . 93
5.8.3 High-Resolution mode and channel coding . 97
5.9 Tables and constants . 97
5.9.1 Band tables index . 97
5.9.2 Low delay MDCT windows. 98
5.9.2.1 Frame size 2,5 ms . 98
5.9.2.2 Frame size 5 ms . 98
5.9.2.3 Frame size 10 ms . 98
5.9.3 SNS quantization . 99
5.9.4 Temporal noise shaping . 100
5.9.5 Long term postfiltering . 100
5.9.6 Spectral data. 101
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6 ETSI TS 103 634 V1.3.1 (2021-10)
6 Source code description. 101
6.1 Overview .
...