1、SMPTE ENGINEERING GUIDELINE - D. EG 17-2002 Revision of EG 17-1997 I O I B-C ha n Electroacoustical Response for Preparing Magnetic Masters for Transfer to 16-mm or 35/32-mm Monaural Photog rap hic Film Page 1 of 4 pages 1 Scope This guideline specifies the electroacoustical frequency response chara
2、cteristic of the monitor system when making magnetic masters intended for transfer to 16-mm photographic negative tracks. 2 Definitions 2.1 complete sound reproduction system: Represented diagramatically in figure 1 and used in studio dubbing theaters, laboratory review rooms, and indoor theaters, g
3、enerally considered to consist of an A- and B-chain. 2.2 preemphasized audio track An audio rec-ord, either magnetic or photographic, which is intended for playback over normally deemphasized playback systems. 2.3 A-chain (transducer system): That part of a motion-picture audio system shown in figur
4、e 1, ex- tending from the transducer to the input terminals of the main fader. 8 ehrin L A ehrin 1- 4 r I I t 1 1 I Non-svnc Magnetic I I E-1 Il I I I Main I fader Crossover network Photographic I Pre-ampli fiers and equalizers I I Screen Figure 1 - Complete theatrical sound reproducing system I l I
5、 I I I l I I I Copyright O 2002 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartcdaie Ave., White Plains, NY 10607 (914) 761-1100 Approved July 26,2002 EG 17-1997 2.4 B-chain (final chain): That pari of a motion-picture sound reproduction system shown in figure 1, commencing fro
6、m the input terminals of the main fader and terminating at any position in the listening area of the room or auditorium at which sound-pressure measurements are taken. 2.5 electroacoustical response: The electro-acoustical response of the final chain is the sound-pres- sure level expressed in decibe
7、ls with respect to an arbitrary reference pressure over a given frequency range measured at a given position in the listening area when wide-band pink noise is applied to the input terminals of the main fader. 2.6 wide-band pink noise: A continuous spectrum noise having constant energy per constant
8、percent- age bandwidth and gaussian probability distribution of instantaneous values, having a bandwidth exceeding the frequency range of interest (typically extending from 31.5 Hz to 12.5 kHz). 3 Method of measurement 3.1 The electroacoustical response shall be measured by generating wide-band pink
9、 noise on the monitor at a level of 85 dBC, slow reading. Measure the acoustical output with a calibrated microphone intended for use in the diffuse field together with an audio-frequency real-time spectrum analyzer, covering the spectrum in 1M-octave bands. 3.2 The electroacoustical response shall
10、be an average of the response measured according to 3.1 at an adequate number of locations in the room where monitoring occurs. 4 Characteristic 4.1 For record monitoring, where magnetic masters are being prepared with preemphasis for making photographic negatives, both the photographic A-chain and
11、the B-chain deemphasis in the monitoring chain are required as shown in table 1 and figure 2. 4.2 Because of the room gain reverberation component and high-frequency attenuation in air (propor- tional to the signal patch length), the measured frequency response should have a slightly elevated high-f
12、requency response in a small dubbing theater. Table 2 gives approximate correction factors which should be added numerically to the characteristic curve in table 1 and figure 2. Page 2 of 4 pages EG 17-1 997 40 63 125 250 500 I 2 2.5 3.15 4 5 6.3 8 IO Figure 2 - A- + Bchain characteristic Table 1 -
13、A- + B-chain electroacoustical response (dB) P ree mp h asked Tolerance Frequency audio track + dB - 40 - 7.0 5 8 63 - 3.0 5 7 125 O 4 4 250 O 4 4 500 O 4 4 1 O00 O 4 4 2000 - 1.0 4 4 2500 - 3.0 4 4 31 50 - 5.0 4 4 4000 - 7.5 4 4 5000 -1 0.5 4 4 6300 -1 4.0 4 4 71 O0 -16.0 4 4 8000 -1 8.0 4 4 9000 -
14、20.5 4 4 1 O000 -23.0 4 4 Page 3 of 4 pages EG 17-1 997 Table 2 - Approximate correction factors for auditorium size, dB Frequency Number of seats 10 30 150 500 1 O00 1500 2000 2000 O O O O O O O 4000 1.5 1 .o 0.5 O -0.5 -1 .o -1.5 8000 3.0 2.0 1 .o O -1 .o -2.0 -3.0 NOTE - For conversion to room vo
15、lume in cubic feet, a figure of 190 ft3/seat, the average of many U.S. theaters, may be used. Annex A (informative) Additional data This guideline is not intended to provide a standard for the playback characteristics of the photographic track, due to the fact that 16-mm film is used in such varied
16、facilities. Such screenings are in classrooms where the internal speaker of the projector is used and the sound track has to compete with the projector noise; in churches where the acoustics are often a compromise; in television receivers where the speaker in the TV set has its limitations: or in sm
17、all screening theaters. It has been found in practice that when using the standard Academy monitor characteristic (as described in this guideline) for preparing monaural masters for photographic tracks, a good quality track is obtained for virtually all screening situations. Generally, 16-mm project
18、ors have manual tone controls which may be adjusted according to the acoustical conditions of the screening. Under good screening conditions, a center positioning of the tone controls will produce a good-sounding track. It is recommended that a 6- or 7-kHz low-pass filter and a 70-Hz high-pass filte
19、r be inserted during the transfer from magnetic film to 16-mm photographic negative to reduce the effects of cross-modulation distortion. Annex B (informative) Bibliography ANSI S .i 1-1986 (R1998), Octave-Band and Fractional Octave-Band Analog and Digital Filters, Specifications for ANSI S1.13-1995 (R1999), Measurement of Sound Pressure Levels in Air SMPTE 202M-1998, Motion Pictures- B-Chain Electroacoustic Response - Dubbing Theaters, Review Rooms and Indoor Theaters SMPTE 21 4M-1999, Motion-Picture Film (35-mm) -Photographic Audio Reproduction Characteristics Page 4 of 4 pages
