1、BRITISH STANDARD BS 5550-7.4.2: 2000 Incorporating Amendment No.1 Cinematography Part 7: Production and presentation Section 7.4: Sound Subsection 7.4.2: Specification for maximum recording levels for commercials and trailers ICS 37.060.99 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COP
2、YRIGHT LAWBS 5550-7.4.2:2000 This British Standard, having been prepared under the direction of the Consumer Products and Services Sector Committee, was published under the authority of the Standards Committee and comes into effect on 15 September 2000 BSI 5 July 2002 The following BSI references re
3、late to the work on this standard: Committee reference CPW/36 Draft for comment 99/703287 DC ISBN 0 580 33209 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee CPW/36, Cinematography, upon which the following bodies were
4、represented: Association of Motion Picture Sound British Kinematograph, Sound and Television Society Broadcasting Entertainment Cinematograph and Theatre Union The following bodies were also represented in the drafting of the standard, through subcommittees and panels: Cinema Exhibitions Association
5、 Society of Film Distributors Co-opted members Amendments issued since publication Amd. No. Date Comments 13695 5 July 2002 Change to sound recording level measurement in 3.2BS 5550-7.4.2:2000 BSI 5 July 2002 i Contents Page Committees responsible Inside front cover Foreword ii 1S c o p e 1 2T e r m
6、 s a n d d e f i n i t i o n s 1 3R e c o r d i n g l e v e l 1 4 Method of measurement 2 Annex A (informative) Typical recording and replay levels 4 Bibliography 5 Figure 1 Method of measurement 2 Table 1 M-type frequency weighting 2 Table 2 Typical six-channel calibration 3BS 5550-7.4.2:2000 ii BS
7、I 5 July 2002 Foreword This British Standard has been prepared by Technical Committee CPW/36. This British Standard should be used in conjunction with the standards that cover the reproduction of motion-picture sound, A-chain and B-chain, including BS 5550-7.4.1:1990 (ISO 2969:1987). A recommended r
8、eplay 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 ar
9、e 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. Owing to their competitive nature, many motion-picture commercials and trailers make sustained use of the highest recording level pos
10、sible 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 exp
11、ected from the average cinema. This standard is intended to promote sensible control and limitation of the sound recording level of commercials and trailers, so that a better match between the sound levels of commercials, trailers, and main features is maintained, and so that confidence in the valid
12、ity of the recommended replay level is re-established. The standard specifies separate recording levels for commercials and trailers. Both specifications may be subsequently amended in response to changing practice within the industry. This publication does not purport to include all the necessary p
13、rovisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 5 and a back cover. The
14、BSI copyright notice displayed in this document indicates when the document was last issued.BS 5550-7.4.2:2000 BSI 5 July 2002 1 1 Scope This British Standard specifies maximum sound recording levels for cinema commercials and trailers. The specified method of measurement is suited to the motion-pic
15、ture environment where the sound recording is measured over its duration, with suitable frequency weighting and integration. NOTE 1 The method of measurement specified allows assessment of the subjective loudness and annoyance of the sound recording when replayed at the recommended replay level in r
16、ooms calibrated in accordance with BS 5550-7.4.1:1990. NOTE 2 Typical recording and replay levels are discussed in annex A. 2 Terms and definitions For the purposes of this British Standard, the following definitions apply. 2.1 pink noise noise whose power spectral density is inversely proportional
17、to frequency 2.2 reference level modulation level equivalent to 50 % modulation of optical variable-area soundtrack, 20 dBFS (digital domain) and 185 nW/m (magnetic domain), measured using an average responding meter and a steady-state tone NOTE 100 % modulation of optical variable-area soundtrack i
18、s equivalent to a dimensional modulation width of 838.2 m. 2.3 reference pink noise pink noise, band-limited to 20 Hz to 20 kHz, set at the reference level, using an average responding meter 2.4 recommended replay level sound pressure level (C-weighted with slow response) that the sound system shoul
19、d produce at the main seating area of the room with reference pink noise NOTE For example, a sound system set to a recommended replay level of 85 dBC will produce a sound pressure level of 85 dBC at the main seating area of the room with reference pink noise. 2.5 M-type filter function as defined in
20、 Table 1 NOTE 1 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 This filter function has also been found to be useful for the purpose of assessing the human response to the loudness
21、 and annoyance of motion-picture soundtracks in calibrated rooms. 3 Recording level 3.1 Commercials When measured in accordance with clause 4, the sound recording level of commercials shall not exceed 82 dBL eq(M) . 3.2 Trailers When measured in accordance with clause 4, the sound recording level of
22、 trailers shall not exceed 85 dBL eq(M) .BS 5550-7.4.2:2000 2 BSI 5 July 2002 Table 1 M-type frequency weighting 4 Method of measurement 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 met
23、hod of measurement would be a costly procedure requiring a number of calibrated microphones with placement-averaging techniques in a room calibrated in accordance with BS 5550-7.4.1. The results would be of low accuracy and low repeatability. Frequency Gain Tolerance Hz dB dB 31 35.5 2.0 63 29.5 1.4
24、 100 25.4 1.0 200 19.4 0.85 400 13.4 0.7 800 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 +2.8, Figure 1 Method of meas
25、urementBS 5550-7.4.2:2000 BSI 5 July 2002 3 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 which represents that channels recommended replay level, and then
26、implement M-type frequency weighting. NOTE 1 Absolute sound pressure levels can be electrically represented by reference to a known level which represents 20 Pa (0 dBSPL). NOTE 2 A typical six-channel calibration is shown in Table 2. Table 2 Typical six-channel calibration 4.2.2 Scalar channel summa
27、tion Rectify and square the scaled M-type weighted signals of each audio channel, and then sum the signals together. NOTE This procedure ensures that the channel summation is scalar (ignoring phase) rather than vector. It therefore simulates multi-sourced, broad-band, reverberant-field, acoustical s
28、ummation. 4.2.3 Loudness equivalent level circuit Measure the mean of the scalar sum over the duration of the sound recording and take its square root. NOTE This will give a true, long-term, root-mean-square (r.m.s.) value representative of an absolute sound pressure level with M-type frequency weig
29、hting. 4.2.4 Result Determine the sound recording level, x, in decibels (loudness equivalent with M-type frequency weighting) dBL eq(M) , using the following equation: Channel Sound pressure level dBC Left 85 Centre 85 Right 85 Left surround 82 Right surround 82 Subwoofer 85 where p is the sound pre
30、ssure level determined in 4.2.3; p 0 is the known level which represents 20 Pa (0 dBSPL). x 20log 10 p p 0 - =BS 5550-7.4.2:2000 4 BSI 5 July 2002 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
31、than the recommended replay level when playing main features, but 8 dB to 12 dB lower than 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 o
32、f dialogue. It is thought that the difference of 2 dB to 3 dB for main features is due to 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. A number
33、of motion-picture sound recordings have been measured using the method specified in clause 4 of this standard. The mean sound recording level of the main features was found to be 82 dBL eq(M) , whereas the mean sound recording level of the unlimited commercials was found to be 88 dBL eq(M) , with so
34、me at 95 dBL eq(M) .BS 5550-7.4.2:2000 BSI 5 July 2002 5 Bibliography Standards publications BS 5550-7.4.1:1990, Cinematography Part 7: Production and presentation Section 7.4: Sound Subsection 7.4.1: Specifications and measurements for the B-chain electro-acoustic response of motion-picture control
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