ISO 21727:2004

INTERNATIONAL ISO
STANDARD 21727
First edition
2004-10-01
Cinematography — Method of
measurement of perceived loudness
of motion-picture audio material
Cinématographie — Méthode de mesure de l'intensité sonore perçue
pour les films cinématographiques

Reference number
©
ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Method of measurement. 2
4.1 General. 2
4.2 Procedure. 3
Annex A (informative) Typical recording and replay levels . 5
Bibliography . 6

Foreword
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ISO 21727 was prepared by Technical Committee ISO/TC 36, Cinematography.
iv © ISO 2004 – All rights reserved

Introduction
This International Standard should be used in conjunction with the standards that cover the reproduction of
motion-picture sound, A-chain and B-chain, including ISO 2969.
A recommended replay level architecture exists for most current cinema sound formats. This matches a
specific recorded modulation level with a specific sound-pressure level at the main seating position in a room
designed in accordance with BS 5550-7.4.1. The noise and over-modulation points of each sound format are
positioned to allow for a wide range of signal components to be recorded and faithfully reproduced at a valid
absolute level as part of a motion-picture soundtrack.
Perhaps due to their competitive nature, many motion-picture commercials and trailers make sustained use of
the highest recording level possible for the format. Consequently, many exhibitors now find the need to reduce
the replay level to a point much lower than the recommendation. This has caused uncertainty as to the validity
of the recommended replay level, which in turn creates problems in matching dubbing theatre sound to that
expected from the average cinema.
This standard is intended to assist in assessing the subjective loudness of motion-picture sound so that a
better match between the sound levels of commercials, trailers and main features is maintained, and so that
confidence in the validity of the recommended replay level is re-established.

INTERNATIONAL STANDARD ISO 21727:2004(E)

Cinematography — Method of measurement of perceived
loudness of motion-picture audio material
1 Scope
This International Standard specifies a method of measurement of motion-picture sound that allows
assessment of the subjective loudness and annoyance of the sound recording when replayed at the
recommended replay level in rooms aligned with the characteristics of ISO 2969. The specified method of
measurement assesses the entire duration of the sound recording with suitable channel summation,
frequency weighting and time integration.
NOTE Typical recording and replay levels are discussed in Annex A.
...