1、 ISO 2016 Cinematography Method of measurement of perceived loudness of short duration motion-picture audio material Cinmatographie Mthode de mesure de lintensit sonore percue pour les films cinmatographiques de courte dure INTERNATIONAL STANDARD ISO 21727 Second edition 2016-05-01 Reference number
2、ISO 21727:2016(E) ISO 21727:2016(E)ii ISO 2016 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2016, 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 mechanica
3、l, 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 ISOs member body in the country of the requester. ISO copyright office Ch. de Blandonnet 8 CP 401 CH-1214 Vernier, Geneva, Switz
4、erland Tel. +41 22 749 01 11 Fax +41 22 749 09 47 copyrightiso.org www.iso.org ISO 21727:2016(E)Foreword iv Introduction v 1 Scope . 1 2 Normative references 1 3 T erms 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 weightin
5、g . 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 ISO 2016 All rights reserved iii Contents Page ISO 21727:2016(E) Foreword ISO (the International Organization for Standardizat
6、ion) 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 r
7、epresented 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
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10、ing 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 m
11、eaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs 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
12、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 ISO 21727:2016(E) Introduction This International Standard is intended to be used in conjunction with the International Standards
13、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
14、 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. P
15、erhaps 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 un
16、certainty 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 mat
17、ch 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 2016 All rights reserved v Cinematography Method of measurement of perceived loudness of short duration motion-picture a
18、udio material 1 Scope This International Standard specifies a method of measurement of short duration 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
19、 ISO 2969. The specified method of measurement assesses the entire duration of the sound recording, typically commercials and trailers that do not exceed 3 min in length, with suitable channel summation, frequency weighting and time integration. It does not specify a maximum recommended level for su
20、ch material and is solely aimed at describing a measurement method. NOTE Typical recording and replay levels are discussed in Annex A. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For the d
21、ated reference, only the edition cited applies. For the undated reference, the latest edition of the referenced document (including any amendments) applies. ISO 22234, Cinematography Relative and absolute sound pressure levels for motion-picture multi- channel sound systems Measurement methods and l
22、evels applicable to analog photographic film audio, digital photographic film audio and D-cinema audio 3 T erms a nd definiti ons For the purposes of this document, the following terms and definitions apply. 3.1 reference level modulation level equivalent to 50 % modulation of optical variable-area
23、soundtrack, 20 dB (level relative to digital full-scale) in the digital domain and 185 nW/m in the magnetic domain, measured using an average responding meter and a steady-state tone Note 1 to entry: 100 % modulation of a single track of a two-track variable-area soundtrack has a dimensional modulat
24、ion of 838,2 m (0,033 in). 3.2 reference pink noise pink noise, band-limited to 20 Hz to 20 kHz, set at the reference level, using an average responding meter 3.3 pink noise stochastic signal having a continuous spectrum from at least 20 Hz to 20 kHz with equal energy 0,5 dB per one-third octave of
25、frequency and a Gaussian probability distribution of instantaneous amplitude INTERNATIONAL ST ANDARD ISO 21727:2016(E) ISO 2016 All rights reserved 1 ISO 21727:2016(E) 3.4 recommended replay level sound-pressure level (C-weighted with slow response) that the sound system should produce in the main s
26、eating area of the room with reference pink noise Note 1 to entry: For example, a sound system set to a recommended replay level of 85 dB (C-frequency-weighted sound-pressure level relative to 20 Pa) will produce a sound-pressure level of 85 dB (C-weighted) in the main seating area of the room with
27、reference pink noise. 3.5 M-type frequency weighting filter function as defined in Table 1 Note 1 to entry: This filter function is based on a filter recommended by the International Telecommunications Union for the assessment of background noise in audio programmes. Note 2 to entry: This filter fun
28、ction has also been found to be useful for the purpose of assessing the human response to the loudness and annoyance of motion-picture soundtracks in calibrated rooms. Table 1 M-type frequency weighting Frequency Gain Tolerance Hz dB dB 31 35,5 2,0 63 29,5 1,4 100 25,4 1,0 200 19,4 0,85 400 13,4 0,7
29、 800 7, 5 0,55 1 000 5,6 0,5 2 000 0,0 0,5 3 150 3,4 0,5 4 000 4,9 0,5 5 000 6,1 0,5 6 300 6,6 0,0 7 100 6,4 0,2 8 000 5,8 0,4 9 000 4,5 0,6 10 000 2,5 0,8 12 500 5,6 1,2 14 000 10,9 1,4 16 000 17, 3 1,65 20 000 27, 8 2,0 31 500 48,3 2,82 ISO 2016 All rights reserved ISO 21727:2016(E) 4 Method of me
30、asurement 4.1 General The measurement shall be carried out in the electrical domain in accordance with 4.2, which follows the steps shown in Figure 1. NOTE An acoustical method of measurement would be impractical and provide results of low accuracy and low repeatability. Figure 1 Method of measureme
31、nt 4.2 Procedure 4.2.1 Input calibration and M-type frequency weighting Scale each input channel independently to normalize the reference level of the recording (recorded test tone) to a level that represents that channels recommended replay level as provided by ISO 22234, and then implement M-type
32、frequency weighting. NOTE 1 Absolute sound-pressure levels can be electrically represented by reference to a known level which represents 20 Pa. NOTE 2 A typical six-channel calibration is shown in Table 2. Table 2 Typical six-channel calibration Channel Sound-pressure level a dB Left 85 Centre 85 R
33、ight 85 Left surround 82 Right surround 82 Subwoofer (LFE) 95 aC-frequency-weighted sound-pressure level relative to 20 Pa. 4.2.2 Scalar channel summation Rectify and square the scaled M-type weighted signals of each audio channel, and then sum the signals together. NOTE This procedure ensures that
34、the channel summation is scalar (ignoring phase) rather than vector. It therefore simulates multi-sourced, broad-band, reverberant-field, acoustical summation. 4.2.3 Loudness-equivalent level Measure the mean of the scalar sum over the duration of the sound recording (typically, first frame of actio
35、n to last frame of action) and take its square root. ISO 2016 All rights reserved 3 ISO 21727:2016(E) 4.2.4 Calculation Determine x, the loudness equivalent level with M-type frequency weighting, using Formula (1): (1) wherep is the level as determined in 4.2.3;p 0 is the known level which represent
36、s 20 Pa.4 ISO 2016 All rights reserved ISO 21727:2016(E) Annex A (informative) Typical recording and replay levels It has been found that exhibitors often prefer a replay level in the region 2 dB to 3 dB lower than the recommended replay level when playing main features, but 8 dB to 12 dB lower than
37、 the recommended replay level when playing commercials and trailers. The reduced replay level used for commercials is sometimes left inadvertently for the main feature, and this can reduce the intelligibility of dialogue. It is thought that the difference of 2 dB to 3 dB for main features is due to
38、the typical tastes of those of the audio industry compared with those of the general public. The 8 dB to 12 dB difference for commercials and trailers is thought to be due to their competitive nature. The loudness equivalent levels of a number of motion-picture sound recordings have been measured us
39、ing the method specified in Clause 4. The mean of the loudness equivalent levels of the main features was found to be 82 dBL eq(M) , whereas the mean of the loudness equivalent levels of the unlimited commercials was found to be 88 dBL eq(M) . ISO 2016 All rights reserved 5 ISO 21727:2016(E) Bibliog
40、raphy 1 ISO 2969, Cinematography B-chain electro-acoustic response of motion-picture control rooms and indoor theatres Specifications and measurements 2 BS 5550-7.4.2:2000, Cinematography Part 7: Production and presentation. Section 7.4: Sound. Subsection 7.4.2: Specification for maximum recording l
41、evels for commercials and trailers 3 IEC 61260, Electroacoustics Octave-band and fractional-octave-band filters 4 IEC 61672-1, Electroacoustics Sound level meters Part 1: Specifications 5 IEC 61672-2, Electroacoustic Sound level meters Part 2: Pattern evaluation tests6 ISO 2016 All rights reserved ISO 21727:2016(E) ISO 2016 All rights reserved IC S 37.060.99 Price based on 6 pages
