ISO 21727:2016

INTERNATIONAL ISO
STANDARD 21727
Second edition
2016-05-01
Cinematography — Method of
measurement of perceived loudness of
short duration motion-picture audio
material
Cinématographie — Méthode de mesure de l’intensité sonore percue
pour les films cinématographiques de courte durée
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – 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 . 3
4.1 General . 3
4.2 Procedure . 3
4.2.1 Input calibration and M-type frequency weighting . 3
4.2.2 Scalar channel summation . 3
4.2.3 Loudness-equivalent level . 3
4.2.4 Calculation . 4
Annex A (informative) Typical recording and replay levels . 5
Bibliography . 6
Foreword
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The committee responsible for this document is ISO/TC 36, Cinematography.
This second edition cancels and replaces the first edition (ISO 21727:2004), of which it constitutes a
minor revision.
iv © ISO 2016 – All rights reserved

Introduction
This International Standard is intended to be used in conjunction with the International Standards
that cover the reproduction of motion-picture sound, A-chain and B-chain, including ISO 2969 and
ISO 22234.
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 ISO 2969 and ISO 22234. 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 International 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 21727:2016(E)
Cinematography — Method of measu
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