ISO 21727:2004
(Main)Cinematography — Method of measurement of perceived loudness of motion-picture audio material
Cinematography — Method of measurement of perceived loudness of motion-picture audio material
ISO 21727:2004 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.
Cinématographie — Méthode de mesure de l'intensité sonore percue pour les films cinématographiques
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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 21727:2004(E)
©
ISO 2004
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ISO 21727:2004(E)
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ISO 21727:2004(E)
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
© ISO 2004 – All rights reserved iii
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ISO 21727:2004(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 21727 was prepared by Technical Committee ISO/TC 36, Cinematography.
iv © ISO 2004 – All rights reserved
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ISO 21727:2004(E)
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.
© ISO 2004 – All rights reserved v
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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.
...
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