1、 Copyright 2010 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 3 Barker Avenue, White Plains, NY 10601 (914) 761-1100 Approved October 20, 2010 Correction to Section 1 Scope made on February 6, 2012 Table of Contents Page Foreword . 2 Intellectual Property 2 1 Scope . 32 Conformance Notat
2、ion . 33 Normative Reference . 34 Definitions 45 Method of Measurement 66 Characteristic Amplitude Responses with Respect to Frequency . 7Annex A Additional Data (Informative) . 10Annex B Bibliography (Informative) . 19Page 1 of 3 pages SMPTE ST 202:2010 Revision of ANSI/SMPTE 202M-1991 SMPTE STANDA
3、RD for Motion-Pictures Dubbing Stages (Mixing Rooms), Screening Rooms and Indoor Theaters B-Chain Electroacoustic Response SMPTE ST 202:2010 Page 2 of 19 pages Foreword SMPTE (the Society of Motion Picture and Television Engineers) is an internationally-recognized standards developing organization.
4、Headquartered and incorporated 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 Committ
5、ees is open to all with 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 ST 202 was pr
6、epared by Technology 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 Standard. However, attention is drawn to the possibility that some of the elements of this document may be the subj
7、ect of patent rights. SMPTE shall not be held responsible for identifying any or all such patent rights. SMPTE ST 202:2010 Page 3 of 19 pages 1 Scope This standard specifies the measurement methods and characteristic electroacoustic frequency response of the B-chain of motion-picture dubbing theater
8、s (mixing rooms), screening rooms, and indoor theaters whose room volume exceeds 125 cu. m. (4414 cu. 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 in
9、stallation to installation, and from position-to-position within an installation. This standard does not cover that part of the motion-picture sound system extending from the transducer to the input source audio selector. 2 Conformance Notation Normative text is text that describes elements of the d
10、esign 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 doe
11、s not contain any conformance keywords. All text in this document is, by default, normative, except: the Introduction, any section explicitly labeled as “Informative“ or individual paragraphs that start with “Note:” The keywords “shall“ and “shall not“ indicate requirements strictly to be followed i
12、n 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 no
13、t 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 defi
14、ned 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 (
15、“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 doc
16、ument shall be as follows: Normative prose shall be the authoritative definition; Tables shall be next; followed by formal languages; then figures; and then any other language forms. 3 Normative Reference Note: All references in this document to other SMPTE documents use the current numbering style
17、(e.g. SMPTE ST 208:1992) although, during a transitional phase, the document as published (printed or PDF) may bear an older designation (such as ANSI/SMPTE 208M-1992). Documents with the same root number (e.g. 208) and publication year (e.g. 1992) are functionally identical. The following standard
18、contains provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of a
19、pplying the most recent edition of the standard indicated below. ANSI/ASA S1.13-2005, Measurement of Sound Pressure Levels in Air SMPTE ST 202:2010 Page 4 of 19 pages 4 Definitions 4.1 complete sound reproduction system: Represented diagrammatically in Figures 1 and 2 and used in indoor theaters and
20、 screening rooms and in motion-picture sound post-production facilities such as dubbing theaters, mix rooms and ADR control rooms. The complete system in an indoor theater or review room is generally considered to consist of an A-chain and a B-chain. 4.2 pre-emphasized audio track: An audio record,
21、either magnetic or photographic, containing high-frequency boost equalization, which is intended for playback over de-emphasized theater playback systems. 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
22、 versions of this standard. (See Section 4.10 and Annex A.10.) 4.3 wide-range audio track: An audio record, either magnetic, analog photographic or digital, which is intended for playback over theater playback systems aligned to this standard, This characteristic was previously referred to as Curve-
23、X (see Section 4.9). Such tracks are recorded without fixed pre- and de-emphasis. Analog wide-range sound-tracks invariably use noise reduction companding technology. 4.4 A-chain (transducer system): That part of a motion-picture audio system extending as far as the input source selector, as shown i
24、n Figures 1 and 2. 4.5 B-chain (final chain): That part of a motion-picture sound reproduction system, as shown in Figures 1 and 2, commencing at the input sourceaudio selector and terminating in the listening area. Figure 1 Complete theatrical audio reproducing chain Traditional Film Formats SMPTE
25、ST 202:2010 Page 5 of 19 pages Figure 2 Complete theatrical audio reproducing chain Digital Cinema 4.6 pink noise: A stochastic signal having a continuous spectrum with equal energy per equal logarithmic interval of frequency, and with a Gaussian probability distribution of instantaneous amplitude (
26、see Section 5.4). 4.7 wide-band pink noise: Pink noise having a bandwidth exceeding the normal acoustic frequency range. A suitable 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 av
27、eraging technique. 4.8 electroacoustic response: The electroacoustic response of the B-chain is the spatially and temporally averaged sound pressure level measured in 1/3-octave bands expressed in decibels with respect to reference level (see Annex A.9) when wide-band pink noise is applied to the in
28、put source selector (see Figures 1 and 2). The electroacoustic response is computed as a spatial and temporal average over the listening area using one of the methods given in Annex A.4. 4.9 Curve-X and X-Curve: Previous versions of this standard defined a B-chain characteristic referred to as Curve
29、-X for wide-range sound-tracks, also known as the X-Curve. 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. 4.10 Curve-
30、N: Previous versions of this standard defined a 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 Annex A.10). SMPTE ST 202:2010 Page 6 of 19 pages 5 Method of Measurement 5.1 The electroacoustic resp
31、onse 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 SMPTE ST 202:2010 Page 7 of 19 pages 5.2 Sound pressure level (SPL) vs. frequency measurements (see Annex A) shall be
32、 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 producers location. In rooms with a single primary listening position, care should be taken that this is not an aberrant locatio
33、n. 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 theaters, at a minimum with the position S as
34、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 Annex A.3.5). An extra series of measurement positions will have
35、 to be added if the theater has a balcony. 5.3 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 s
36、creen loudspeaker(s). 5.4 A suitable single loudspeaker auditorium sound pressure level with wide-band pink noise is 85 dB SPL C-weighted and slow reading (see Annex A.9). 5.5 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
37、 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, Table 4. 5.6 A system for playing contemporary stereo films will generally employ a minimum of four wide-range channels: screen left, cente
38、r, 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 sound-tracks are played have the surround
39、 channel separated into two or three separate channels, left rear and right rear, or left rear, center 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 u
40、sing one or more sub-woofers. Some rooms may be equipped with two intermediate screen channels, one between left and center, and one between center and right. Regardless of the number of channels, each channel or bank shall be measured separately in turn and the equalization adjusted if necessary. 6
41、 Characteristic Amplitude Responses with Respect to Frequency 6.1 The electroacoustic response of the B-chain for screen and surround channels shall be as listed in Table 1 and shown in Figure 5 within the tolerances given. Note that this characteristic is for a medium sized theater (with between, s
42、ay, 200 and 500 seats) with average reverberation behavior. See Annex A.5 for a discussion of modifications required to this characteristic for larger and smaller spaces and for surround loudspeaker arrays. 6.2 It is recognized that there are a few older sound systems still in use in theaters which
43、cannot meet the centerline 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 Annex A.6. SM
44、PTE ST 202:2010 Page 8 of 19 pages Table 1 B-chain screen and surround channel characteristic for medium sized theater (see Annex A.5e and A.5f for modification factors and surround characteristic A.6) Center frequencies of 1/3-octave bands Hz Level dB Tolerances dB + 31.5 -2 3 7 40 -1 3 6 50 0 3 5
45、63 0 3 4 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 1000 0 3 3 1250 0 3 3 1600 0 3 3 2000 0 3 3 2500 -1 3 3 3150 -2 3 3 4000 -3 3 3 5000 -4 3 3 6300 -5 3 3 8000 -6 3 3 10000 -7 3 4 12500 -9 3 5 16000 -11 3 6 SMPTE ST 202:2010 Page 9 o
46、f 19 pages Figure 5 B-chain screen and surround characteristic for medium sized theater (see Annex A.5e and A.5f for modification factors and surround characteristic) 6.3 Low-frequency effects channel intended for sub-woofer playback The bandwidth of the low-frequency effects channel on a modern sou
47、nd-track 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 sound-track cut-off is extremely steep, so a suitable sub-woofer need have little response above 125 Hz. Many rooms have one or more dominant resonant frequencies
48、within the low-frequency effects channel bandwidth. If not damped, this can lead to a characteristic low-frequency “ringing” every time the sound-track contains low-frequency information. Most cinema B-chain processors have at least one parametric equalizer for use within the sub-woofer bandpass. Af
49、ter adjustment, the response between 25 Hz and 120 Hz shall be flat to within + 3 dB. SMPTE ST 202:2010 Page 10 of 19 pages Annex A Additional Data (Informative) A.1 Factors outside the scope of this standard This 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 theaters. However, compliance with this standard is a necessary but not sufficient condition for the complete achievement of high-quality sound reproducti
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