ISO/IEC 23003-4:2025

International
Standard
ISO/IEC 23003-4
Third edition
Information technology — MPEG
2025-03
audio technologies —
Part 4:
Dynamic range control
Technologies de l'information — Technologies audio MPEG —
Partie 4: Contrôle de gamme dynamique
Reference number
© ISO/IEC 2025
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© ISO/IEC 2025 – All rights reserved
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Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions .1
3.2 Symbols .3
4 Mnemonics. 3
5 Technical overview . 4
6 DRC decoder . 5
6.1 DRC decoder configuration .5
6.1.1 Overview .5
6.1.2 Description of logical blocks .6
6.1.3 Derivation of peak and loudness values .10
6.2 Dynamic DRC gain payload . . 15
6.3 DRC set selection . 15
6.3.1 Overview . 15
6.3.2 Pre-selection based on Signal Properties and Decoder Configuration .16
6.3.3 Selection based on requests .18
6.3.4 Final selection .21
6.3.5 Applying multiple DRC sets.21
6.3.6 Album mode .21
6.3.7 Ducking and Loudness Leveling . 22
6.3.8 Precedence . 22
6.4 Time domain DRC application . 22
6.4.1 Overview . 22
6.4.2 Framing . 23
6.4.3 Time resolution. 23
6.4.4 Time alignment . 23
6.4.5 Decoding .24
6.4.6 Gain modifications and interpolation .27
6.4.7 Spline interpolation . 34
6.4.8 Look-ahead in decoder . 35
6.4.9 Node reservoir . 36
6.4.10 Applying the compression .37
6.4.11 Dynamic equalization . 40
6.4.12 Multi-band DRC filter bank .42
6.5 Sub-band domain DRC .45
6.6 Generation of DRC gain values at the decoder . 49
6.6.1 Overview . 49
6.6.2 Description of logical blocks . 50
6.6.3 Algorithmic details .51
6.6.4 Combining parametric and non-parametric DRCs . 58
6.7 Loudness equalization support . 58
6.8 Equalization tool .59
6.8.1 Overview .59
6.8.2 EQ payloads .59
6.8.3 EQ filter elements . 60
6.8.4 EQ set selection .61
6.8.5 Application of EQ set .61
6.9 Complexity management . 68
6.9.1 General . 68
6.9.2 DRC and downmixing complexity estimation . 68

© ISO/IEC 2025 – All rights reserved
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6.9.3 EQ complexity estimation .70
6.10 Loudness normalization .71
6.10.1 Overview .71
6.10.2 Loudness normalization based on target loudness .71
6.10.3 Loudness Leveling .74
6.11 DRC in streaming scenarios .74
6.11.1 DRC configuration .74
6.11.2 Error handling . 75
6.12 DRC configuration changes during active processing . 75
7 Syntax . 76
7.1 Syntax of DRC payload .76
7.2 Syntax of DRC gain payload .76
7.3 Syntax of static DRC payload . 77
7.4 Syntax of DRC gain sequence . 102
7.5 Syntax of parametric DRC tool . 102
7.6 Syntax of equalization tools . 108
8 Reference software .
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