ISO 22234-2005 Cinematography - Relative and absolute sound pressure levels for motion-picture multi-channel sound systems - Measurement methods and levels appl.pdf

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1、 Reference number ISO 22234:2005(E) ISO 2005INTERNATIONAL STANDARD ISO 22234 First edition 2005-11-15 Cinematography Relative and absolute sound pressure levels for motion-picture multi-channel sound systems Measurement methods and levels applicable to analog photographic film audio, digital photogr

2、aphic film audio and D-cinema audio Cinmatographie Niveaux de pression sonore relatifs et absolus pour les systmes de films cinmatographiques sonores multicanaux Mthodes de mesure et niveaux applicables aux films sonores photographiques analogiques, aux films sonores photographiques numriques et lau

3、dio de D-cinma ISO 22234:2005(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the ed

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6、t the address given below. ISO 2005 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address bel

7、ow or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2005 All rights reservedISO 22234:2005(E) ISO 2005 All rights reserved i

8、ii 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

9、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 matt

10、ers 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 circul

11、ated 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 responsib

12、le for identifying any or all such patent rights. ISO 22234 was prepared by Technical Committee ISO/TC 36, Cinematography. INTERNATIONAL STANDARD ISO 22234:2005(E) ISO 2005 All rights reserved 1 Cinematography Relative and absolute sound pressure levels for motion-picture multi-channel sound systems

13、 Measurement methods and levels applicable to analog photographic film audio, digital photographic film audio and D-cinema audio 1 Scope This International Standard specifies the measurement methods and wide-band sound pressure levels for motion-picture control rooms, review rooms, and indoor theatr

14、es. Together with ISO 2969, it is intended to assist in standardization of reproduction of motion-picture sound in such rooms. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For u

15、ndated references, the latest edition of the referenced document (including any amendments) applies. ISO 2969:1987, Cinematography B-chain electro-acoustic response of motion-picture control rooms and indoor theatres Specifications and measurements IEC 60268-17:1990, Sound system equipment Part 17:

16、Standard volume indicators IEC 61672-1:2002, Electroacoustics Sound level meters Part 1: Specifications 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 absolute sound pressure spatially averaged sound pressure level of a single channel of a t

17、heatrical sound system measured with broadband pink noise at the reference electrical level as a stimulus NOTE The 0 dB (reference) level for sound pressure is 20 N/m 2 . 3.2 average responding meter meter which provides a voltage indication proportional to the average value of the rectified signal,

18、 with ballistics as described in IEC 60268-17 3.3 bass extension technique of taking low-frequency information from a film sound-track, processing it, and sending it to a sub-woofer, as opposed to an LFE channel NOTE See A.3. ISO 22234:2005(E) 2 ISO 2005 All rights reserved3.4 B-chain final chain th

19、at part of a motion-picture sound reproduction system, as shown in Figure 1 for a typical film system, commencing at the input terminals of the main fader and terminating in the listening area defined in Figure 2 in which sound pressure level measurements are taken NOTE See A.7. 3.5 electroacoustic

20、response B-chain spatially averaged frequency response measured in one-third octave bands as described in ISO 2969 NOTE The electroacoustic response is expressed in decibels. 3.6 LFE channel discrete low-frequency effects channel, normally having an upper bandwidth between 80 Hz and 125 Hz 3.7 pink

21、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 3.8 reference electrical level voltage measured by an average responding voltmeter of wide-band pink noise using

22、 a measurement band pass filter of 22 Hz to 22 kHz bandwidth when the test signal is at reference recorded level, and when the fader is at its normal setting NOTE See A.5 and A.7. 3.9 reference recorded level level of pink noise equivalent to 50 % modulation on an analog photographic sound-track, or

23、 the equivalent level on a digital photographic sound-track or a digital cinema (D-cinema) sound-track (typically in each case 20 dB below 100 % modulation) 3.10 relative sound pressure level sound pressure level of one channel when compared with another during reproduction of the wide-band test sig

24、nal of 3.1, as opposed to the sound pressure level in one frequency range when compared with another 3.11 wide-band pink noise pink noise having a bandwidth exceeding the normal acoustic frequency range NOTE A suitable test signal should have a frequency response flat to within 0,5 dB when measured

25、in one-third octave bands with centre frequencies from 25 Hz to 20 kHz with an integrating averaging technique. 3.12 wide-band sound level meter meter which conforms to IEC 61672-1 ISO 22234:2005(E) ISO 2005 All rights reserved 3Key 1 A-chain 8 insertion point for test signals 2 B-chain 9 B-chain eq

26、ualizer 3 non-sync 10 power amplifier 4 magnetic 11 crossover network 5 photographic 12 loudspeakers 6 preamplifiers and equalizers 13 screen 7 main fader 14 auditorium acoustics Figure 1 Complete film-based theatrical sound reproduction system Key 1 screen 2 limits of seating area Figure 2 Plan vie

27、w, theatre auditorium ISO 22234:2005(E) 4 ISO 2005 All rights reserved4 Test methods 4.1 Electroacoustic response The electroacoustic response of each channel should be measured and confirmed to comply with ISO 2969 before measurement of relative and absolute sound pressure levels. 4.2 Measuring equ

28、ipment The sound pressure level of screen and surround channels should be made using a wide-band sound level meter set to C-weighting and slow response. The sound pressure level of the sub-woofer channel should be made using a one-third octave real-time analyser, or a sound level meter with a one-th

29、ird octave filter set. 4.3 Test signal The test signal should be wide-band pink noise, fed into the sound system one channel at a time. The pink noise should be inserted into the system prior to the main fader, or at an equivalent point. The fader should be set to its normal setting (see A.5 and A.7

30、). 4.4 Sound pressure level The sound pressure level should be measured in at least one position for each screen and surround channel and the measurements for each channel then spatially averaged. If a single location only is selected, it should be position S as shown in Figure 2. All measurement lo

31、cations should be within the normal seating area as shown in the hatched area in Figure 2. The sub-woofer sound pressure level should be measured in at least four positions and averaged over time intervals of no less than 30 s. 4.5 Screen channels The relative sound pressure level of each screen cha

32、nnel should be within 0,5 dB of the absolute sound pressure level. 4.6 Surround channel(s) If there is one single surround channel, then the sound pressure level when playing the test signal should equal that of the absolute sound pressure level. If there are two independent surround channels, left

33、and right, then each should display a sound pressure level such that when they are simultaneously fed the same in- phase test signal the sum should equal the absolute sound pressure level. For two surround channel systems, the individual sound pressure level for each channel will usually be 3 dB bel

34、ow the absolute sound pressure level. (See A.8.) This procedure will ensure compatibility for theatres with fewer surround playback channels where the surround information is combined. With three or more surround channels, the individual channel reproduction levels should be set up to be equal to on

35、e channel of a two surround channel system. 4.7 Sub-woofer LFE channel, playback of discrete digital photographic sound-track or D-cinema sound-track The sub-woofer channel, when compared with a wide-band screen channel, should show 10 dB of “in-band” gain when viewed on a real-time analyser, i.e. a

36、 level in its pass band 10 dB higher than the level in the pass band of the screen channel. See Figures 3 and A.1. 4.8 Sub-woofer channel, for playback of matrix-encoded analog photographic sound-track with bass extension playback processing The bass extension sub-woofer channel, when compared with

37、a wide-band screen channel, should show the same level, i.e. should show no “in-band” gain when viewed on a real-time analyser. See Figures 4, A.2 and A.3. If the test signal is applied to both the centre screen channel and the sub-woofer channel simultaneously, the analyser should show 3 dB of “in-

38、band” gain in the frequency area common to both transducers. ISO 22234:2005(E) ISO 2005 All rights reserved 5Key 1 RTA display, single screen channel, wide-band pink noise 2 RTA display, sub-woofer, wide-band pink noise Figure 3 Measurement of subwoofer sound-pressure level, digital LFE sound track,

39、 using real-time analyser Key 1 RTA display, single screen channel, wide-band pink noise 2 RTA display, sub-woofer, wide-band pink noise Figure 4 Measurement of subwoofer sound-pressure level, analog photographic sound track with bass extension playback processing, using real-time analyser 5 Referen

40、ce level The reference level defined as in 3.1 and measured as specified in this International Standard should be 85 dB (C-weighted), for normal theatrical operation. ISO 22234:2005(E) 6 ISO 2005 All rights reservedAnnex A (informative) General information A.1 Subwoofers and sound-level meters While

41、 a wide-band sound level meter is suitable for measuring sound pressure levels of screen and surround channels, it is not suitable for measurement of sub-woofer levels. The first reason for this is the differing low-pass cut-off of different sub-woofers. For example, if pink noise and a sound level

42、meter were used to set equal levels between one loudspeaker extending to 125 Hz and another extending to 250 Hz, the sound pressure levels in the pass band of each loudspeaker would be significantly different, as shown in Figure A.1. Key 1 level error 2 RTA display aComparison of different sub-woofe

43、rs. bSame sound pressure level. Figure A.1 Setting sound pressure levels of sub-woofers with sound level meters can create level ambiguity A second reason to avoid use of wide-band sound level meters for sub-woofer measurement is the loose tolerance at low frequencies associated with the inexpensive

44、 meters typically used. A sound level meter incorporating a one-third-octave filter set may provide acceptable results. ISO 22234:2005(E) ISO 2005 All rights reserved 7 A.2 In-band gain Using a real-time analyser is the only accurate method of measuring band-limited signal levels. In-band gain is th

45、e relative level within the band pass of interest, as seen on a real-time analyser display. A.3 Bass extension With analog photographic sound-tracks, unwanted noises can occur at very low frequencies, below approximately 50 Hz. Two main causes of these noises are ground noise reduction timing errors

46、 causing “thumping”, and low-frequency “streaking” noise caused by bad print washing. For this reason, some analog processors strip out low-frequency information, and process it to remove low-level unwanted components. This processed output is then sent to a dedicated sub-woofer. This technique is k

47、nown as bass extension. A.4 Subwoofer polarity It is frequently very difficult to determine the best polarity of a sub-woofer by conventional methods of checking the speaker cone polarity. The effective phase may change with frequency, especially with a discrete digital sub-woofer channel where filt

48、er slopes may cause changing phase with frequency. For this reason, it is recommended that sub-woofer polarity be evaluated with pink noise sent to centre and sub-woofer channels simultaneously. The best result should be selected of the two polarities by looking at the resultant combination signal m

49、easured with a real-time analyser. In some cases, there may be no apparent signal level change regardless of selected polarity of sub-woofer with respect to centre front with discrete signals, and in this case optimum polarity should be selected from evaluation of a composite signal through the analog photographic B-chain. A.5 Fader setting The vast majority of theatre B-chains have a calibrated fader, which allows the operator to return to a known mark. In many cases, there is a scale ranging from 0 to 1