1、STD-SMPTE 2Lb-ENGL 194h 8357401 0003438 008 SMPTE STANDARD SMPTE 21 6-1 998 Revision of ANSIISMPTE 216-1985 for Motion-Picture Film (35-mm) - Four-Track Striped Release Prints - Recorded Characteristic of Magnetic Audio Records 1 Scope This standard specifies the recorded characteristic of magnetic
2、audio records on 35-mm four-track striped motion-picture release prints, when reproduced at 24 frames per second or approximately 90 ft (27 m) per minute. 2 Recorder characteristic With a constant-amplitude sine-wave signal applied to the input of the recording system, the relative characteristic in
3、 effective values of the short circuit magnetric flux versus frequency shall decrease with increasing frequency proportionately to the imped- ance of a parallel combination of a capacitance and a resistance having time constants of 35 and 3180 ps (see note 1). The characteristic defined above is obt
4、ained by the following equation: I 1 +(27LCh)2f2 1+ 1/(27czi)2f2 Lp=co-1ologlo where Lq, is the recorded relative short circuit magnetic flux level in decibels, f is the frequency in hertz for which L is computed, 21 is the low- frequency time constant of 3180 ps, zh is the high- frequency time cons
5、tant of 35 ps, and Co is a constant with a value of 0.19424 calculated to make L = O at the reference frequency of 1 O00 Hz. The approximate numerical values are given in the table (see note 2). Frequency, Hz f 31.5 40 50 80 1 O0 160 400 1 O00 2500 4000 6300 8000 10 O00 12 500 16 O00 3 Tolerances Pa
6、ge 1 of 2 pages Relative level Lh + 5.66 + 4.29 + 3.21 + 1.63 + 1.16 + 0.59 + 0.23 0.00 - 0.95 - 2.29 - 4.46 - 5.93 - 7.47 - 9.13 -1 1 .O7 Magnetic audio records on the film shall be recorded to the characteristic specified in clause 2 within the tolerances given in figure 1. NOTES 1 A time constant
7、 is a shorthand notation, such as illus- trated by a frequency response curve, having a shape which results from a time constant of one or more microseconds. This is a convenient way of defining a response curve and is not intended as a recommended electrical circuit. 2 The corresponding reproducing
8、 characteristic is that which gives a flat response. 3 It has been shown that a straight 35-ps curve should be used for optimal use of the magnetic medium. It is recog- nized, however, that it is necessary for the immediate future to continue to add 3180 ps because some theater equip- ment is unable
9、 to compensate for the low end. CopyngMQ 1998 by THE SOCIEPI OF MOTION PICTURE ANDTELEVISION ENGINEERS 595 W. Harisdale Ave., While Plains, NY 10607 (914) 761-1100 Approved September 24,1998 SMPTE 216-1998 - m -0 W o z U W J O I- Y a +2 +I O -1 -2 -3 -4 -5 40 50 100 500 Ik FREQUENCY (HZ) 5k 6.3k IOk 16k Figure 1 - Tolerances on recorded levels Page 2 of 2 pages
