ISO/IEC 23003-4:2020
(Main)Information technology — MPEG audio technologies — Part 4: Dynamic range control
Information technology — MPEG audio technologies — Part 4: Dynamic range control
This document specifies technology for loudness and dynamic range control. It is applicable to most MPEG audio technologies. It offers flexible solutions to efficiently support the widespread demand for technologies such as loudness normalization and dynamic range compression for various playback scenarios.
Technologies de l'information — Technologies audio MPEG — Partie 4: Contrôle de gamme dynamique
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INTERNATIONAL ISO/IEC
STANDARD 23003-4
Second edition
2020-06
Information technology — MPEG
audio technologies —
Part 4:
Dynamic range control
Technologies de l'information — Technologies audio MPEG —
Partie 4: Contrôle de gamme dynamique
Reference number
ISO/IEC 23003-4:2020(E)
©
ISO/IEC 2020
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ISO/IEC 23003-4:2020(E)
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ISO/IEC 23003-4:2020(E)
Contents Page
Foreword . vi
Introduction . vii
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and mnemonics. 1
3.1 Terms and definitions . 1
3.2 Mnemonics . 3
4 Symbols (and abbreviated terms) . 3
5 Technical overview . 4
6 DRC decoder . 6
6.1 DRC decoder configuration . 6
6.1.1 Overview . 6
6.1.2 Description of logical blocks . 7
6.1.3 Derivation of peak and loudness values. 12
6.2 Dynamic DRC gain payload . 16
6.3 DRC set selection . 16
6.3.1 Overview . 16
6.3.2 Pre-selection based on Signal Properties and Decoder Configuration . 17
6.3.3 Selection based on requests . 20
6.3.4 Final selection . 22
6.3.5 Applying multiple DRC sets . 23
6.3.6 Album mode . 23
6.3.7 Ducking. 23
6.3.8 Precedence . 24
6.4 Time domain DRC application . 24
6.4.1 Overview . 24
6.4.2 Framing . 24
6.4.3 Time resolution . 25
6.4.4 Time alignment . 25
6.4.5 Decoding . 26
6.4.6 Gain modifications and interpolation . 29
6.4.7 Spline interpolation . 35
6.4.8 Look-ahead in decoder . 36
6.4.9 Node reservoir . 37
6.4.10 Applying the compression . 38
6.4.11 Dynamic equalization . 41
6.4.12 Multi-band DRC filter bank . 43
6.5 Sub-band domain DRC . 47
6.6 Generation of DRC gain values at the decoder . 51
6.6.1 Overview . 51
6.6.2 Description of logical blocks . 52
6.6.3 Algorithmic details . 53
6.6.4 Combining parametric and non-parametric DRCs . 60
6.7 Loudness equalization support . 61
6.8 Equalization tool . 62
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ISO/IEC 23003-4:2020(E)
6.8.1 Overview . 62
6.8.2 EQ payloads . 62
6.8.3 EQ filter elements . 63
6.8.4 EQ set selection . 64
6.8.5 Application of EQ set . 64
6.9 Complexity management . 72
6.9.1 General . 72
6.9.2 DRC and downmixing complexity estimation . 72
6.9.3 EQ complexity estimation . 74
6.10 Loudness normalization . 75
6.10.1 Overview . 75
6.10.2 Loudness normalization based on target loudness . 76
6.11 DRC in streaming scenarios . 79
6.11.1 DRC configuration . 79
6.11.2 Error handling . 79
6.12 DRC configuration changes during active processing . 79
7 Syntax . 81
7.1 Syntax of DRC payload . 81
7.2 Syntax of DRC gain payload . 81
7.3 Syntax of static DRC payload . 82
7.4 Syntax of DRC gain sequence. 109
7.5 Syntax of parametric DRC tool. 110
7.6 Syntax of equalization tools . 117
8 Reference software . 131
8.1 Reference software structure . 131
8.1.1 General . 131
8.2 Bitstream decoding software . 131
8.2.1 General . 131
8.2.2 MPEG-D DRC decoding software . 132
9 Conformance . 132
9.1 General . 132
9.2 Conformance testing . 132
9.2.1 Conformance test data and test procedure . 132
9.2.2 Naming conventions . 134
9.2.3 File format definitions . 136
9.3 Encoder Conformance for MPEG-D DRC bitstreams . 138
9.3.1 Characteristics and test procedure . 138
9.3.2 Configuration payload . 139
9.3.3 Interface payload . 153
9.3.4 Frame Payload . 156
9.3.5 Requirements depending on profiles and levels . 157
9.4 Decoder conformance test categories and conditions . 158
9.4.1 General . 158
9.4.2 Conformance test categories . 158
9.4.3 Conformance test conditions . 158
Annex A (normative) Tables . 167
Annex B (normative) External Interface to DRC tool . 207
Annex C (informative) Audio codec specific information . 220
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ISO/IEC 23003-4:2020(E)
Annex D (informative) DRC gain generation and encoding . 225
Annex E (informative) DRC set selection and adjustment at decoder . 236
Annex F (informative) Loudness normalization . 243
Annex G (informative) Peak limiter . 244
Annex H (informative) Equalization . 249
Annex I (normative) Profiles and levels. 251
Annex J (informative) Reference software disclaimer . 260
Annex K (informative) Reference software . 261
Bibliography . 262
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ISO/IEC 23003-4:2020(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) or the
IEC list of patent declarations received (see http://patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT)
see www.iso.org/iso/foreword.html.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information Technology,
Subcommittee SC 29, Coding of audio, picture, multimedia, and hypermedia.
This second edition cancels and replaces the first edition (ISO 23003-4:2015), which has been
technically revised. It also incorporates the Amendments ISO 23003-4:2015/Amd.1:2017 and
ISO 23003-4:2015/Amd.2:2017. The main changes compared to the previous edition are as follows:
— Amendments to the previous edition that include enhancements, definitions of profiles and levels,
reference software, and conformance are integrated.
A list of all parts in the ISO/IEC 23003 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body.
A complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/IEC 23003-4:2020(E)
Introduction
Consumer audio systems and devices are used in a large variety of configurations and acoustical
environments. For many of these scenarios, the audio reproduction quality can be improved by
appropriate control of content dynamics and loudness.
This document provides a universal dynamic range control tool that supports loudness normalization.
The DRC tool offers a bitrate efficient representation of dynamically compressed versions of an audio
signal. This is achieved by adding a low-bitrate DRC metadata stream to the audio signal. The DRC tool
includes dedicated sections for clipping prevention, ducking, and for generating a fade-in and fade-out
to supplement the main dynamic range compression functionality. The DRC effects available at the DRC
decoder are generated at the DRC encoder side. At the DRC decoder side, the audio signal may be played
back without applying the DRC tool, or an appropriate DRC tool effect is selected and applied based on
the given playback scenario.
Loudness normalization is fully integrated with DRC and peak control to avoid clipping. A metadata-
controlled equalization tool is provided to compensate for playback scenarios that impact the spectral
balance, such as downmix or DRC. Furthermore, the DRC tool supports metadata-based loudness
equalization to compensate the effect of playback level changes on the spectral balance.
The International Organization for Standardization (ISO) and International Electrotechnical
Commission (IEC) draw attention to the fact that it is claimed that compliance with this document may
involve the use of a patent.
ISO and IEC take no position concerning the evidence, validity and scope of these patent rights
The holders of these patent rights have assured ISO and IEC that they are willing to negotiate licences
under reasonable and non-discriminatory terms and conditions with applicants throughout the world.
In this respect, the statements of the holders of these patent rights are registered with ISO and IEC.
Information may be obtained from the patent database available at www.iso.org/patents.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights other than those in the patent database. ISO and IEC shall not be held responsible for
identifying any or all such patent rights.
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INTERNATIONAL STANDARD ISO/IEC 23003-4:2020(E)
Information technology — MPEG audio technologies —
Part 4:
Dynamic range control
1 Scope
This document specifies technology for loudness and dynamic range control. It is applicable to most
MPEG audio technologies. It offers flexible solutions to efficiently support the widespread demand for
technologies such as loudness normalization and dynamic range compression for various playback
scenarios.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 14496-12, Information technology — Coding of audio-visual objects — Part 12: ISO base media
file format
ISO/IEC 14496-26:2010, Information technology — Coding of audio-visual objects — Part 26: Audio
Conformance
ISO/IEC 23008-3:2019, Information technology — High efficiency coding and media delivery in
heterogeneous environments — Part 3: 3D audio
ISO/IEC 23091-3, Information technology — Coding-independent code points — Part 3: Audio
3 Terms, definitions and mnemonics
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 14496-12 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1.1
DRC sequence
series of DRC gain values that can be applied to one or more audio channels
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ISO/IEC 23003-4:2020(E)
3.1.2
DRC set
defined set of DRC sequences that produce a desired effect if applied to the audio signal
3.1.3
album
collection of audio recordings that are mastered in a consistent way
Note 1 to entry: Traditionally, a collection of songs released on a Compact Disk belongs into this category, for
example.
3.1.4
conformance test bitstream
bitstream used for testing the conformance of MPEG-D DRC compliant audio decoders
3.1.5
conformance test case
conformance test category and a combination of one or more conformance test conditions for which a
conformance test sequence is provided
3.1.6
conformance test condition
condition which applies to properties of a conformance test sequence in order to test a certain
functionality of the MPEG-D DRC decoder
3.1.7
conformance test criteria
one or more conformance test tools and corresponding parameters applied to verify the conformance
for a certain conformance test sequence
3.1.8
conformance test sequence
set of a conformance test bitstream, a decoder setting, an input audio file and a corresponding reference
file
3.1.9
decoder input parameters
input parameters that are supplied to an MPEG-D DRC decoder in addition to a conformance test
bitstream, a decoder interface bitstream and an input audio file
3.1.10
decoder setting
combination of a decoder interface bitstream and decoder input parameters that are supplied to an
MPEG-D DRC decoder
3.1.11
input DRC set selection parameters
input parameter set for testing of a DRC gain decoder instance
Note 1 to entry: This parameter set is solely used for conformance testing in the context of the DRC gain decoder
conformance test category (DrcGainDec).
3.1.12
reference audio file
decoded counterpart of a conformance test bitstream, a decoder setting and an input audio file
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ISO/IEC 23003-4:2020(E)
3.1.13
reference DRC set selection parameters
decoded counterpart of a conformance test bitstream and a decoder setting fed to the DRC set selection
process
Note 1 to entry: This parameter set is an intermediate result of an MPEG-D DRC compliant decoder
implementation solely used for conformance testing in the context of the DRC selection process test category
(DrcSelProc).
3.1.14
reference file
reference audio file or reference DRC set selection parameters
3.2 Mnemonics
bslbf bit string, left bit first, where “left” is the order in which bit strings are written in the
ISO/IEC 14496 series
NOTE Bit strings are written as a string of 1s and 0s within single quote marks, for
example '1000 0001'. Blanks within a bit string are for ease of reading and have no
significance.
byte_align() number of bits to fill for byte alignment at the offset of n bits:
byte_align(n) = 8 ceil (n/8) – n
uimsbf unsigned integer, most significant bit first
vlclbf variable length code, left bit first, where “left” refers to the order in which the
variable length codes are written
bit(n) a bit string with n bits in the same format as bslbf
unsigned int(n) an unsigned integer with n bits in the same format as uimsbf
signed int(n) a signed integer with n bits, most significant bit first
mod modulo operator: (x mod y) = x-y floor (x/y)
sizeof(x) size operator that returns the bit size of a field x
TRUE/FALSE values of Boolean data type, which correspond to numerical 1 and 0, respectively
4 Symbols
a filter coefficient
i
b band index of DRC filter bank (starting at 0)
b filter coefficient
i
deltaTmin smallest permitted DRC gain sample interval in units of the audio sample interval
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ISO/IEC 23003-4:2020(E)
f cross-over frequency in Hz
c
f cross-over frequency expressed as fraction of the audio sample rate
c,norm
f (s) cross-over frequency of audio decoder sub-band s expressed as fraction of
c,norm,SB
the audio sample rate
NOTE The cross-over frequency is the upper band edge frequency of the sub-
band.
f audio sample rate in Hz
s
NOTE If an audio decoder is present, it is the sample rate of the decoded time-
domain audio signal.
M DRC frame size in units of the audio sample interval 1/f
DRC s
N maximum permitted number of DRC samples per DRC frame
DRC
NOTE Identical to the number of intervals with a duration of deltaTmin per DRC
frame.
N codec frame size in units of the audio sample interval 1/f
Codec s
π ratio of a circle’s circumference to its diameter
s audio decoder sub-band index (starting at 0)
z complex variable of the z-transform
5 Technical overview
The technology described in this document is called the “DRC tool”. It provides efficient control of
dynamic range, loudness, and clipping based on metadata generated at the encoder. The decoder can
choose to selectively apply the metadata to the audio signal to achieve a desired result. Metadata for
dynamic range compression consists of encoded time-varying gain values that can be applied to the
audio signal. Hence, the main b
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