ISO/IEC 23091-3:2018

INTERNATIONAL ISO/IEC
STANDARD 23091-3
First edition
2018-04
Information technology — Coding-
independent code points —
Part 3:
Audio
Technologies de l'information — Points de code indépendants du
codage —
Partie 3: Audio
Reference number
©
ISO/IEC 2018
© ISO/IEC 2018
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ii © ISO/IEC 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Code points and usage . 2
4.1 General . 2
4.2 Applicability . 3
5 Principles for definition and referencing of code points . 3
5.1 Code point encoding and defaults . 3
5.2 Externally defined values . 3
5.3 Reference format . 3
5.4 Uniform Resource Name format . 4
6 Audio code point definitions . 4
6.1 Loudspeaker index and speaker channel position . 4
6.2 Loudspeaker layout index and channel configuration. 7
6.3 Loudspeaker positioning.12
6.4 Program loudness level .17
6.5 Anchor loudness level .17
6.6 Range of loudness .18
6.7 Top of loudness range .18
6.8 Maximum of momentary loudness level .18
6.9 Maximum of short-term loudness level .18
6.10 Short-term loudness level .18
6.11 Peak level .18
6.12 Compressor characteristic .19
Bibliography .22
© ISO/IEC 2018 – All rights reserved iii

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. In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1.
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 ISO documents 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 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).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on 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 the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/IEC JTC1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
1)
Together with ISO/IEC 23091-1 and ISO/IEC 23091-2 , this first edition of ISO/IEC 23091-3 cancels and
replaces ISO/IEC 23001-8:2016, which has been technically revised.
A list of all parts in the ISO/IEC 23091 series can be found on the ISO website.
1) Under preparation. Stage at time of publication: ISO/IEC DIS 23091-2:2017.
iv © ISO/IEC 2018 – All rights reserved

Introduction
There is a need to identify some characteristics of media that are logically independent of the
compression format (for example, aspects that relate to the sourcing or presentation or the role of the
media component). These media characteristics have typically been documented by fields that take an
encoded value or item selected from an enumerated list, herein called code points.
Prior to the existence of the parts of this standard, the specification of these fields was copied into
every document that needed them, sometimes with new values being added.
This past practice has raised a number of issues, including the following.
a) A lack of a formal way to avoid conflicting assignments being made.
b) Having additional values defined in later documents that may be practically used with older
compression formats, without clear formal applicability of these new values.
c) Any update or correction of code point semantics can incur significant effort to update all places in
which the code point is specified, instead of enabling a single central specification to apply.
d) The choice of reference for other specifications (such as container or delivery formats) not being
obvious; wherein a formal reference to a compression format specification appears to favour that
one format over others, and also appears to preclude definitions defined in other compression
format specifications.
e) Burdensome maintenance needs to ensure that a reference to material defined in a compression
format specification is maintained appropriately over different revisions of the referenced format
specification, as the content of a compression format specification may change over time and is
ordinarily not intended as a point of reference for defining such code points.
The parts of this series provide a central definition of such code points to address these issues. In
this document, code points that are used for audio are specified. ISO/IEC 23091-1 specifies a Uniform
Resource Name (URN) format that can be used with the code points defined in all parts of the series,
including this one.
© ISO/IEC 2018 – All rights reserved v

INTERNATIONAL STANDARD ISO/IEC 23091-3:2018(E)
Information technology — Coding-independent code
points —
Part 3:
Audio
1 Scope
This document defines various code points and fields that establish properties of an audio stream
that are independent of the compression encoding and bit rate. These properties could describe the
appropriate interpretation of decoded audio data or could, similarly, describe the characteristics of
such signals before the signal is compressed by an encoder that is suitable for compressing such an
input signal.
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 23091-1, Information technology — Coding independent code points — Part 1: Systems
Rec. ITU-R BS.1771-1, Requirements for loudness and true-peak indicating meters
EBU R 128, Loudness normalization and permitted maximum level of audio signals
EBU Tech 3341, Loudness Metering: ‘EBU mode’ metering to supplement Loudness normalization in
accordance with EBU R 128
EBU Tech 3342, Loudness Range: A measure to supplement Loudness normalisation in accordance with
EBU R 128
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
channel
Ch
conceptual representation of an audio signal for coding or transmission as it may be used within the
digital signal processing chain of an audio codec
3.2
dynamic range compressor
DRC
process that modifies the amplitude of an audio signal
© ISO/IEC 2018 – All rights reserved 1

3.3
K-weighted
frequency weighting by means of a two-stage filter
Note 1 to entry: As defined in Reference [3].
3.4
LKFS
loudness, K-weighted, relative to nominal full scale
Note 1 to entry: As defined in Reference [3].
3.5
loudspeaker
LS
physical loudspeaker with a given geometric position relative to the listener and, if applicable, a
label or name
Note 1 to entry: Even though the loudspeaker names used in this document each describe one discrete
loudspeaker position, some loudspeaker signals may, in practice, be rendered on a loudspeaker array consisting
of multiple loudspeakers which are all driven with the same audio signal, for example, in a theatrical setting.
3.6
loudspeaker index
association of a loudspeaker geometric position to a given index
3.7
loudspeaker layout
set of loudspeakers with a specific constellation of geometric positions meant for authoring or play-
back of audio content
3.8
lousdspeaker layout index
association of a loudspeaker layout to a given index
4 Code points and usage
4.1 General
This Clause identifies the code points defined in this document, as listed in Table 1 with cross-references
to the subclause in which each is specified.
Table 1 — List of code points
Name Abstract Subclause
OutputChannelPosition Audio channel assignment 6.1
ChannelConfiguration Audio channel configuration 6.2
LoudspeakerGeometry Audio loudspeaker geometry 6.3
LoudspeakerElevation Audio loudspeaker elevation 6.3
LoudspeakerAzimuth Audio loudspeaker azimuth
...