1、 Table of Contents Page Foreword . 2 Intellectual Property 2 Introduction 2 1 Scope 3 2 Conformance Notation 3 3 Normative References 3 4 Definitions . 4 5 Method of Measurement . 7 6 Reference Level 9 Annex A General Information (Informative) 10 Page 1 of 11 pages Relative and Absolute Sound Pressu
2、re Levels for Motion-Picture Multichannel Sound Systems Applicable for Analog Photographic Film Audio, Digital Photographic Film Audio and D-Cinema Copyright 2007 by THE SOCIETY OF SMPTE RECOMMENDED PRACTICE SMPTE RP 200:2012 Revision of RP 200-2002 Copyright 2012 by THE SOCIETY OF MOTION PICTURE AN
3、D TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved April 18, 2012 SMPTE RP 200:2012 Page 2 of 11 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an internationally-recognized standards developing organization. Headquartered and inc
4、orporated in the United States of America, SMPTE has members in over 80 countries on six continents. SMPTEs Engineering Documents, including Standards, Recommended Practices, and Engineering Guidelines, are prepared by SMPTEs Technology Committees. Participation in these Committees is open to all wi
5、th a bona fide interest in their work. SMPTE cooperates closely with other standards-developing organizations, including ISO, IEC and ITU. SMPTE Engineering Documents are drafted in accordance with the rules given in Part XIII of its Administrative Practices. SMPTE RP 200 was prepared by Technology
6、Committee 20F. Intellectual Property At the time of publication no notice had been received by SMPTE claiming patent rights essential to the implementation of this Recommended Practice. However, attention is drawn to the possibility that some of the elements of this document may be the subject of pa
7、tent rights. SMPTE shall not be held responsible for identifying any or all such patent rights. Introduction This section is informative and does not form an integral part of this Engineering Document. The motion picture industry is unique in having the target and capability of ensuring that the aud
8、io heard in the playback theatre matches that heard in the mixroom/dubbing theatre when the content was created. The two main criteria defining the audio environment are frequency response and level. B-chain electroacoustic frequency response is defined in SMPTE ST 202. This companion document cover
9、s a method for measuring and defining the absolute and relative audio level using steady state wideband pink noise. Note that the procedures defined in this document do not apply in the home, with or without picture, as the consumer normally has an uncalibrated and arbitrarily adjusted playback leve
10、l. SMPTE RP 200:2012 Page 3 of 11 pages 1 Scope This practice specifies a measurement method and wideband sound pressure levels for motion-picture dubbing theatres, review rooms, and indoor theatres using steady state wideband pink noise methodology. Together with SMPTE ST 202, it is intended to ass
11、ist in standardization of reproduction of motion-picture sound in such rooms. 2 Conformance Notation 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 potent
12、ially 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 la
13、beled 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 severa
14、l 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
15、“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 th
16、at 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 provis
17、ions (“may“) and need not implement them as described. Unless otherwise specified, the order of precedence of the types of normative information in this document shall be as follows. Normative prose shall be the authoritative definition. Tables shall be next, followed by formal languages, then figur
18、es, and then any other language forms. 3 Normative References The following standards contain provisions which, through reference in this text, constitute provisions of this practice. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to
19、 agreements based on this practice are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. SMPTE ST 202:2010, Motion-Pictures Dubbing Stages (Mixing Rooms), Screening Rooms and Indoor Theatres B-Chain Electroacoustic Response IEC 60268-17 (
20、1990-10), Sound System Equipment Part 17: Standard Volume Indicators SMPTE RP 200:2012 Page 4 of 11 pages 4 Definitions 4.1 absolute sound pressure level the spatially averaged sound pressure level of a single channel of a theatrical sound system measured with broadband pink noise at the reference e
21、lectrical level as a stimulus. The reference level for sound pressure is 20N/m2. 4.2 average responding meter a meter which provides a voltage indication proportional to the average value of the rectified signal, with ballistics as described in IEC 60268-17. 4.3 bass extension the technique of creat
22、ing low-frequency information where there is no dedicated LFE channel, i.e. from an analog film photographic sound-track. The audio is taken from the sound-track, low-pass filtered, processed, and sent to the subwoofer (see Annex A.3). 4.4 B-chain (final chain) that part of a motion-picture sound re
23、production system, as shown in Figures 1 and 2, commencing at the audio input source selector and terminating in the listening area defined in Figure 3 (see Annex A.5 and Annex A.7). Figure 1 Complete theatrical sound reproduction chain (Traditional Film Formats see Annex A.7) SMPTE RP 200:2012 Page
24、 5 of 11 pages Figure 2 Complete theatrical sound reproducing chain (Digital Cinema see Annex A.7) SMPTE RP 200:2012 Page 6 of 11 pages Figure 3 Placement of Sound-Level Meter (See Section 5.4) 4.5 electroacoustic response the electroacoustic response of the B-chain is the spatially averaged frequen
25、cy response measured in 1/3-octave bands expressed in decibels, as described in SMPTE ST 202. 4.6 LFE channel a discrete low-frequency effects channel, having a recommended upper -3 dB band limit of 125 Hz. 4.7 pink noise a stochastic signal having a continuous spectrum with equal energy per equal l
26、ogarithmic interval of frequency, and with a gaussian probability distribution of instantaneous amplitude. 4.8 reference electrical level the voltage measured by an average-responding voltmeter of wideband pink noise using a measurement bandpass filter of 22 Hz to 22 kHz bandwidth when the test sign
27、al is at reference recorded level, and when the main fader is at its normal/calibration setting (see Annex A.5 and Annex A.7). In practice today the reference electrical level is 20 dB below 100% modulation. Measuring microphones within this area. See section 5.4 SMPTE RP 200:2012 Page 7 of 11 pages
28、 4.9 reference recorded level originally defined as the level of pink noise equivalent to 50% modulation on an analog photographic sound-track. Today, the equivalent level on a digital photographic sound-track or a digital cinema (D-Cinema) sound-track (typically in each digital case 20 dB below 100
29、% modulation). 4.10 relative sound pressure level in this context, the sound pressure level of one channel when compared with another during reproduction of the wideband test signal of 4.1, as opposed to the sound pressure level in one frequency range when compared with another. 4.11 wideband pink n
30、oise pink noise having a bandwidth exceeding the normal acoustic frequency range. A suitable wideband pink noise test signal should have a frequency response flat to within + 0.5 dB when measured in 1/3-octave bands with center frequencies from 25 Hz to 20 kHz with an integrating averaging technique
31、. 5 Method of Measurement 5.1 Electroacoustic response confirmation The electroacoustic response of each channel should be measured and confirmed to conform to SMPTE ST 202 before measurement of relative and absolute sound pressure levels. 5.2 Measuring equipment 5.2.1 Screen and Surround channels.
32、The sound pressure level of screen and surround channels is most commonly measured using a wideband sound-level meter set to C-weighting and slow response. In some circumstances, for example an auditorium with aberrant electroacoustic responses at frequency extremes, it can be beneficial to use a ca
33、librated 1/3 octave analyzer to set the primary channels. Using a limited section of the analyzer display and averaging the level within that section can avoid any aberrations at frequency extremes. A wideband pink noise signal has a level 15 dB above that in a single 1/3 octave band. For example, a
34、n 85 dBC wideband pink noise signal equates to 70 dB in each individual 1/3 octave band. A typical window will be 500 Hz to 2 kHz. 5.2.2 Subwoofer. The sound pressure level of the subwoofer channel should be measured using a 1/3-octave real-time analyzer, or a sound-level meter with a built-in 1/3-o
35、ctave filter set. 5.3 Test signal The test signal should be wideband 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, typically at a position at or equivalent to the input source selector. The fader should be set
36、to its normal setting (see Annex A.7) 5.4 Sound pressure level measurement locations 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 shou
37、ld be position S as shown in Figure 3. All sound pressure level measurement locations should be within the seating area as shown in Figure 3. The subwoofer sound pressure level should be measured in at least four positions and averaged over time intervals of not less than 30 seconds. SMPTE RP 200:20
38、12 Page 8 of 11 pages 5.5 Screen channels The relative sound pressure level of each screen channel should be within 0.5dB of the absolute sound pressure level. 5.6 Surround channel(s) If there is one single surround channel, then the sound pressure level when playing the test signal should equal tha
39、t of the absolute sound pressure level. If there are two independent surround channels, left 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. This means that typ
40、ically the sound pressure level for each surround channel array will be 3 dB below the absolute sound pressure level (see Annex 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 ch
41、annels, the individual channel reproduction levels should be set up to be equal to one channel of a two channel surround system. 5.7 Subwoofer LFE channel, playback of discrete digital photographic sound-track or D-Cinema sound-track The subwoofer LFE channel, when compared with a wideband screen ch
42、annel, should show +10 dB of in-band gain when viewed on a real-time analyzer. Therefore, the subwoofer will have the same level in its passband as the level in the passband of a screen channel (see Figure 4 and Annex A.1). Figure 4 Measurement of subwoofer sound-pressure level, digital LFE sound-tr
43、ack, using real-time analyzer 5.8 Subwoofer bass extension channel, for playback of analog photographic sound-track with bass extension playback processing The bass extension subwoofer channel, when compared with a wideband screen channel, should show the same in-band level; i.e. should show no in-b
44、and gain when viewed on a real-time analyzer (see Figure 5, Annex A.2 and Annex A.3). If the test signal is applied to both the center screen channel and the subwoofer channel simultaneously, the analyzer should show 3 dB of in-band gain in the frequency area common to both loudspeakers. RTA display
45、 - Single screen channel - wide-band pink noise 10 dB RTA display - Sub-woofer - wide-band pink noise SMPTE RP 200:2012 Page 9 of 11 pages Figure 5 Measurement of subwoofer sound-pressure level, analog photographic Sound-track with bass extension playback processing, using real-time analyzer 6 Refer
46、ence Level The recommended reference level, as defined in Section 4.1 and measured as specified in this practice, should be 85 dBC for normal theatrical operation. RTA display - Single screen channel - wide-band pink noise RTA display - Sub-woofer - wide-band pink noise SMPTE RP 200:2012 Page 10 of
47、11 pages Annex A General Information (Informative) A.1 Subwoofers and sound-level meters While a wideband sound-level meter is suitable for measuring sound pressure levels of screen and surround channels, it is not suitable for measurement of subwoofer levels. The first reason for this is the differ
48、ing low-pass cut-off of different subwoofers. For example, if pink noise and a sound-level meter were used to set equal levels between one loudspeaker extending to 80 Hz and another extending to 125 Hz, the sound pressure levels in the passband of each loudspeaker would be significantly different, a
49、s shown in Figure A.1. Figure A.1 Setting sound-pressure levels of subwoofers with sound-level meters can create level ambiguity A second reason to avoid use of wideband sound-level meters for subwoofer measurement is the loose tolerance at low-frequencies associated with the inexpensive meters typically used. A sound-level meter incorporating a 1/3-octave filter set may provide acceptable results. A.2 In-band gain Using a real-time analyzer is the only accurate method of measuring band-limited signal levels. In-band gain is the r
