ISO 2969:2015

INTERNATIONAL ISO
STANDARD 2969
Third edition
2015-06-01
Cinematography — B-chain electro-
acoustic reponse of motion-picture
control rooms and indoor theatres —
Specifications and measurements
Réponse électro-acoustique de la chaîne B des salles de contrôle et
d’exploitation cinématographique — Spécifications et mesurages
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Method of measurement . 3
4 Characteristic amplitude responses with respect to frequency . 5
Annex A (informative) Factors outside the scope of this International Standard .8
Bibliography .17
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.
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 meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 36, Cinematography.
This third edition cancels and replaces the second edition (ISO 2969:1987), which has been
technically revised.
iv © ISO 2015 – All rights reserved

Introduction
This International Standard is to be used in conjunction with the relevant standards which cover that
part of the motion picture sound system from the transducer to the input terminals of the main fader.
In this International Standard, normative text is text that describes elements of the design that are
indispensable or contains the conformance language keywords: “shall”, “should”, or “may”. Informative text
is text that is potentially helpful to the user, but not indispensable, and can be removed, changed, or added
editorially without affecting interoperability. Informative text does not contain any conformance keywords.
All text in this document is, by default, normative, except: the Introduction, any section explicitly labelled
as “Informative” or individual paragraphs that start with “Note”.
The keywords “shall” and “shall not” indicate requirements strictly to be followed in order to conform
to the document and from which no deviation is permitted.
The keywords, “should” and “should not” indicate that, among several possibilities, one is recommended
as particularly suitable, without mentioning or excluding others; or that a certain course of action is
preferred but not necessarily required; or that (in the negative form) a certain possibility or course of
action is deprecated but not prohibited.
The keywords “may” and “need not” indicate courses of action permissible within the limits of the document.
The keyword “reserved” indicates a provision that is not defined at this time, shall not be used, and may
be defined in the future. The keyword “forbidden” indicates “reserved” and in addition indicates that the
provision will never be defined in the future.
A conformant implementation according to this document is one that includes all mandatory provisions
(“shall”) and, if implemented, all recommended provisions (“should”) as described. A conformant
implementation need not implement optional provisions (“may”) and need not implement them as described.
Unless otherwise specified, the order of precedence of the types of normative information in this
document are as follows: Normative prose is the authoritative definition; Tables are next; followed by
formal languages; then figures; and then any other language forms.
INTERNATIONAL STANDARD ISO 2969:2015(E)
Cinematography — B-chain electro-acoustic reponse of
motion-picture control rooms and indoor theatres —
Specifications and measurements
1 Scope
This International Standard specifies the measurement methods and characteristic electroacoustic
frequency response of the B-chain of motion-picture dubbing theatres (mixing rooms), screening
3 3
rooms, and indoor theatres whose room volume exceeds 125 m (4,414 ft ). It is intended to assist in
standardization of monitoring and reproduction of motion-picture sound in such rooms. The goal is to
have constant perceived loudness and frequency response from installation to installation, and from
position-to-position within an installation. This International Standard does not cover that part of the
motion-picture sound system extending from the transducer to the input source audio selector.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
complete sound reproduction system
system used in indoor theatres and screening rooms and in motion-picture sound post-production
facilities such as dubbing theatres, mix rooms and ADR control rooms
Note 1 to entry: The complete system in an indoor theatre or review room is generally considered to consist of an
A-chain and a B-chain.
Note 2 to entry: Represented diagrammatically in Figures 1 and 2.
2.2
pre-emphasized audio track
audio record, either magnetic or photographic, containing high-frequency boost equalization, which is
intended for playback over de-emphasized theatre playback systems
Note 1 to entry: Now very rarely used, but found on all films prior to the mid-1970s. Part of the playback de-
emphasis was generated by use of Curve-N in previous versions of this standard (see 2.10 and A.10).
2.3
wide-range audio track
audio record, either magnetic, analogue photographic or digital, which is intended for playback over
theatre playback systems aligned to this International Standard
Note 1 to entry: This characteristic was previously referred as Curve-X (see 2.9). Such tracks are recorded without fixed
pre- and de-emphasis. Analogue wide-range soundtracks invariably use noise reduction companding technology.
2.4
A-chain (transducer system)
part of a motion-picture audio system extending as far as the input source selector, as shown in
Figures 1 and 2
2.5
B-chain (final chain)
part of a motion-picture sound reproduction system, as shown in Figures 1 and 2, commencing at the
input source audio selector and terminating in the listening area
Figure 1 — Complete theatrical audio reproducing chain — Traditional Film Formats
Figure 2 — Complete theatrical audio reproducing chain — Digital Cinema
2 © ISO 2015 – All rights reserved

2.6
pink noise
stochastic signal having a continuous spectrum with equal energy per equal logarithmic interval of
frequency, and with a Gaussian probability distribution of instantaneous amplitude (see 3.4)
2.7
wide-band pink noise
pink noise having a bandwidth exceeding the normal acoustic frequency range
Note 1 to entry: A suitable test signal should have a frequency response flat to within ±0,5 dB when measured in
1/3-octave bands with centre frequencies from 25 Hz to 20 kHz with an integrating averaging technique.
2.8
electroacoustic response
spatially and temporally averaged sound pressure level measured in 1/3-octave bands
expressed in decibels with respect to reference level (see A.9) when wide-band pink noise is applied to
the input source selector (see Figures 1 and 2)
Note 1 to entry: The electroacoustic response is computed as a spatial and temporal average over the listening
area using one of the methods given in A.4.
2.9
Curve-X
X-Curve
B-chain characteristic referred to as Curve-X for wide-range sound tracks, also known as X-Curve
Note 1 to entry: This characteristic typically required some high-frequency equalization boost when older
loudspeakers were in use, but is now easily achievable with contemporary loudspeakers. All contemporary
practice is targeted to the X-Curve.
2.10
Curve-N
B-chain characteristic referred to as Curve-N for use with loudspeakers with much poorer high-
frequency response than those typically now in use (see A.10)
3 Method of measurement
3.1 The electroacoustic response shall be measured with the equipment arranged in accordance with
Figures 3 and 4 (see Annex A).
Figure 3 — Method of measurement of B-chain
Figure 4 — Range of microphone placements
3.2 Sound pressure level (SPL) vs. Frequency measurements (see Annex A) shall be made as follows:
a) On dubbing stages (in mixing rooms), at each of the principal listening positions, such as at the
position of each of the mixing personnel, and at the producer’s location. In rooms with a single
primary listening position, care should be taken that this is not an aberrant location;
b) In screening rooms, at a sufficient number of positions to cover the listening area and to reduce the
standard deviation of measured position-to-position response to less than 3 dB. This will typically
be achieved with four positions;
c) In indoor theatres, at a minimum with the position S as shown in Figure 4, and normally at a sufficient
number of additional other positions to reduce the standard deviation of measured position-to-
position response to less than 3 dB. This will typically be achieved with four positions (see A.3.5).
An extra series of measurement positions will have to be added if the theatre has a balcony.
3.3 Measurements shall be made at a normal seated ear height between 1,0 m and 1,2 m (3.3 ft and
4.0 ft), but not closer than 150 mm (6 in) from the top of a seat, and not closer than 1,5 m (4.9 ft) to any
wall and not closer than 5,0 m (16.4 ft) from the screen loudspeaker(s).
3.4 A suitable single loudspeaker auditorium sound pressure level with wide-band pink noise is 85 dB
SPL C-weighted and slow reading (see A.9).
4 © ISO 2015 – All rights reserved

3.5 The measured level in any 1/3-octave band can be used directly if it exceeds the background noise
in the band by at least 10 dB. If the background noise is between 4 dB and 10 dB below the test signal, the
measurement may be corrected using the techniques described in ANSI/ASA S1.13 (see Table 4).
3.6 A system for playing contemporary stereo films will generally employ a minimum of four wide-
range channels: screen left, centre, and right loudspeaker systems, and a surround channel loudspeaker
system employing a number of individual loudspeakers spaced around the left wall, rear wall and right
wall of the room in such a way as to achieve uniform coverage. Most rooms where digital soundtracks are
played have the surround channel separated into two or three separate channels, left rear and right rear,
or left rear, centre rear and right rear. Such systems are frequently built up out of left wall, left rear, right
rear and right wall banks of speakers. Most of these rooms also have a dedicated low-frequency channel
using one or more sub-woofers. Some rooms may be equipped with two intermediate screen channels,
one between left and centre, and one between centre and right. Regardless of the number of channels,
each channel or bank shall be measured separately in turn and the equalization adjusted if necessary.
4 Characteristic amplitude responses with respect to frequency
4.1 The electroacoustic response of the B-chain for screen and surround channels shall be listed in
Table 1 and shown in Figure 5 within the tolerances given. Note that this characteristic is for a medium-
sized theatre (with between, say 200 and 500 seats) with average reverberation behaviour. See A.5 for a
discussion of modifications required to this characteristic for larger and smaller spaces and for surround
loudspeaker arrays.
4.2 It is recognized that there are a few older sound systems still in use in theatres which cannot meet
the centreline of the standard over the fully extended frequency range. The response standard has been
updated over the years to account for the changes in technology which permit a wider frequency range,
but note the precaution on excessive equalization of older systems in A.6.
Table 1 — B-chain screen and surround channel characteristics for medium-sized theatre
(see A.5 e) and A.5 f) for modification factors and surround characteristics A.6)
Centre frequencies Level Tolerances
of 1/3-octave bands
dB
HZ
+ -
dB
31,5 -2 3 7
40 -1 3 6
50 0 3 3
63 0 3 3
80 0 3 3
100 0 3 3
125 0 3 3
160 0 3 3
200 0 3 3
250 0 3 3
315 0 3 3
400 0 3 3
500 0 3 3
630 0 3 3
800 0 3 3
1 000 0 3 3
1 250 0 3 3
1 600 0 3 3
2 000 0 3 3
2 500 −1 3 3
3 150 −2 3 3
4 000 −3 3 3
5 000 −4 3 3
6 300 −5 3 3
8 000 −6 3 3
10 000 −7 3 3
12 500 −9 3 3
16 000 −11 3 3
6 © ISO 2015 – All rights reserved

Figure 5 — B-chain screen and surround characteristics for medium-sized theatre (see A.5 e)
and A.5 f) for modification factors and surround characteristics)
4.3 The bandwidth of the low-frequency effects channel on a modern soundtrack extends from 5 Hz
to 120 Hz. A linear sub-woofer acoustic response is desirable from approximately 25 Hz to 120 Hz. The
120 Hz soundtrack cut-off is extremely steep, so a suitable sub-woofer need have little response above
125 Hz. For information on subwoofer adjustment refer to ISO 22234:2005.
Many rooms have one or more dominant resonant frequencies within the low-frequency effects channel
bandwidth. If not damped this can lead to a characteristic low-frequency “ringing” every time the
soundtrack contains low-frequency information. Most cinema B-chain processors have at least one
parametric equalizer for use within the sub-woofer bandpass. After adjustment, the response between
25 Hz and 120 Hz shall be flat to within ±3 dB.
Annex A
(informative)
Factors outside the scope of this International Standard
A.1 General
This International Standard was prepared in the belief that an extended and uniform frequency response
is a fundamental component of good sound quality in review rooms and theatres.
However, compliance with this International Standard is a necessary but not sufficient condition for the
complete achievement of high-quality sound reproduction. Subjective judgments of sound quality are
influenced not only by the frequency response of the B-chain (which is the subject of this International
Standard), but also by such factors including but not limited to
a) A-chain performance. For analogue soundtracks, it is important that the A-chain be correctly aligned
within the tolerances of existing standards by the use of the appropriate photographic or magnetic
test film and that relevant electrical de-emphasis be applied where applicable (see Bibliography).
Appropriate alignment includes such parameters as frequency response, signal-to-noise ratio,
wow and flutter, track-to-track crosstalk, and the like. While it may be assumed that an A-chain
for playback of digital film soundtracks or for digital cinema files has an inherently flat frequency
response, quality can still be limited by digital to analogue converters, etc.;
b) electrical performance of the sound system, including available headroom before clipping, hum and
noise, and the like;
c) room acoustics, including reverberation time vs. frequency, echoes (both specular and flutter
types), behind-screen reflections, background noise, and intrusive noise;
d) placement of loudspeaker sources vs. picture; and
e) loudspeaker distortion, and many others.
A.2 Preliminary checks
It is important that preliminary checks for gross acoustic errors be made prior to measuring the electroacoustic
response as described in this International Standard. Typical checks include verification that the loudspeaker
being measured is close enough to the screen to avoid any behind-screen echoes, and verification of speaker
polarity. A wide-band pink noise test signal can be sent to combinations of loudspeakers (for example, L and
C, L and R, C and R) as a simple verification of consistent loudspeaker polarity. The correct polarity (in-phase)
condition is the one producing the greatest bass response from the sum.
Evaluation of uniformity of loudspeaker distribution patterns can be crudely evaluated by ear using a
wide-band pink noise test signal. A more exhaustive numerical analysis of uniformity can be derived by
analysing the point-to-point response as measured in A.3.5.
A.3 Qualifying the accuracy of measurements
A.3.1 Type of Measurement
Measurements of sound fields from loudspeakers in rooms can take many forms. Tone burst, fast Fourier
transform, time-delay spectroscopy, and maximum length sequence analysis may all prove useful,
especially during the design phase of a loudspeaker system. Much of the analysis conducted with these
methods has the object of reducing the effect of room acoustics on the measurements. Analysis using
8 © ISO 2015 – All rights reserved

pink noise with a constant-percentage bandwidth real-time spectrum analyser, such as a 1/3-octave
real-time analyser, on the other hand, includes the influence of room acoustics and has been found to
be most useful and convenient in day-to-day alignment of sound systems. Traditional real-time analysis
has been improved in reliability by the method outlined in this International Standard through the use
of spatial and time averaging, which can yield typical differences as small as ±1 dB from one setup of the
equipment to another.
A.3.2 Background noise
See 3.5.
A.3.3 Maximum sound pressure level caution
Excessive sound pressure levels may risk damage to loudspeakers.
A.3.4 Microphone response, directivity, and mounting
The microphones used for theatre measurements are subjected to three sound fields, all of which will be
taken account of in the measuring process. They are the direct sound field from the loudspeaker, early
reflections, and the reverberant sound field. Substantial errors can be introduced by using microphones
which have large diaphragms, or which have cavities in front of the diaphragm, primarily because their
response to direct sound fields and diffuse sound fields is different. Therefore, small diameter calibrated
microphones are strongly preferred for accuracy over large diameter types
...