1、 1 Scope 1.1 This practice specifies a type U audio frequency test film to be used for adjusting the mechanical and electrical parameters of 16-mm motion-picture magnetic audio reproducers operating at 24 frames per second. NOTE The film velocity of 16-mm film is also commonly stated as 7.2 inches p
2、er second or 183 millimeters per second, and historically stated as 36 feet or 11 meters per minute. 1.2 The International Organization for Standardization recognizes two reference levels for test films type U with a reference level of 185 nWb/m and type E with a reference level of 320 nWb/m in orde
3、r to account for differing meter types in common use in the United States and Europe. 2 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 st
4、andards are subject to revision, and parties to agreements based on this practice are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. ANSI S4.3-1982 (R1992), Method for Measurement of Weighted Peak Flutter of Sound Recording and Reprodu
5、cing Equipment ANSI S4.6-1982 (R1992), Method of Measuring Recorded Flux of Magnetic Sound Records at Medium Wavelengths ANSI/IEEE 152-1992, Audio Program Level Measurement SMPTE 97-1999, Motion-Picture Film (16-mm) 200-Mil Edge Position Magnetic Audio Record SMPTE 109-2003, Motion-Picture Film (16-
6、mm) Perforated 1R and 2R SMPTE 223M-2001, Motion-Picture Film Safety Film 3 Manufacturing 3.1 Film stock 3.1.1 The film stock shall be polyester-base, full-coat, splice-free and in compliance with SMPTE 223M. 3.1.2 Test films shall be made on a base cut and perforated in accordance with SMPTE 109. 3
7、.1.3 The film stock shall be conditioned for 10 days at 20C 3C (68F 5.4F) at a relative humidity of (50 10)% prior to recording. Page 1 of 5 pagesRP 90-2004 Revision of RP 90-1999 Copyright 2004 by THE SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (
8、914) 761-1100 Approved November 8, 2004 SMPTE RECOMMENDED PRACTICE Specifications for Type U Audio Level and Multifrequency Test Film for 16-mm Audio Reproducers, Magnetic Type RP 90-2004 Page 2 of 5 pages 3.2 Magnetic coating 3.2.1 Full-coat film The coating shall extend from edge to edge of the fi
9、lm. 3.2.2 Magnetic particle orientation Because of orientation of the magnetic particles within the coating during manufacture, the film may show a preferred direction for recording. The preferred direction is the direction which shows the greatest high-frequency sensitivity. If there is such a pref
10、erred direction, it shall be marked by means of an arrow faced in the preferred direction on the head and tail of the film. 4 Primary characteristics of test film records 4.1 Test film content This general-purpose, diagnostic, and verification test film consists of the following sections: 1) Referen
11、ce level 2) Azimuth check 3) Pink noise 4) Frequency response 5) Reference level 4.2 Audio record 4.2.1 Track width The audio record shall be recorded so that it extends from one edge of the film to the other. 4.2.2 Azimuth The azimuth of the audio records shall be 90 3 to the reference edge of the
12、film. 4.2.3 Distortion The total harmonic distortion of the recorded reference level tone (5.1) and the frequency response tones (5.4) shall not exceed 0.5%. 4.2.4 Flutter The weighted peak flutter of the audio record shall not exceed 0.1%. Verification of this section shall be made with the film st
13、ock to be used for making these test films, and measured in accordance with ANSI S4.3. 4.2.5 Signal identification Each test section and segment shall be preceded by voice announcements identifying the content at a level whose peak value does not exceed peak level of the frequency series. 4.2.6 Refe
14、rence level A 400-Hz sine-wave tone recorded at the type U reference level of 185 nWb/m is provided at the beginning of the test film, and again at the end, as a check for system linearity and freedom from overload. RP 90-2004 Page 3 of 5 pages 4.2.7 Frequency response section 4.2.7.1 Frequencies Th
15、e audio record on the film shall be a recording which will reproduce at the frequencies specified in 5.4.2 when the linear speed of the film is 24 perforations per second or approximately 36 ft per minute (7.2 in per second or 18.3 cm per second). 4.2.7.2 Selection of frequencies For measurements an
16、d adjustments of frequency response, it has been observed that the mid-frequencies are seldom a problem, but that careful attention is needed at both the low end and the high end to ensure that specified system response is achieved. Accordingly the test film includes the third-octave preferred frequ
17、encies for these two end portions of the spectrum. Through the mid-spectrum the selected frequencies have a wider spacing. Additional frequencies of 14 000 and 16 000 have been added as a convenience in providing more points to define the high end. 4.2.7.3 Duration The duration of frequency response
18、 test segments shall be approximately 10 seconds, except for the 16-kHz tone which shall be approximately 30 seconds for additional azimuth alignment as well as high-frequency equalization adjustment. 5 Test section specifications 5.1 Reference level A 400-Hz 2% sine-wave tone shall be recorded at a
19、 flux level of 185 nWb/m 10 nWb/m ( 0.5 dB) for a duration of approximately 30 seconds. 5.2 Azimuth A sine-wave frequency of 12.5 kHz 2% shall be recorded ahead of the pink noise section, having an absolute short-circuit flux level of 10.63 nWb/m, for a duration of approximately 30 seconds. 5.3 Pink
20、 noise Pink noise shall be recorded for a duration of approximately 30 seconds. The pink noise test signal shall be recorded at such a level that upon playback there is a low statistical probability of peaks exceeding the peak-to-peak amplitude of the reference level. This condition can be verified
21、by observing the reproduction of the pink noise signal on an oscilloscope connected to the playback preamplifier, and comparing it with the peak-to-peak signal indicated by the reference level. The pink noise shall be so recorded that the short-circuit flux level vs frequency conforms to 5.4.2, as m
22、easured in third-octave bands. 5.4 Frequency response 5.4.1 Objectives The mathematical expression specifying the short circuit flux as a function of frequency has been chosen to maximize the capabilities of the magnetic recording system and to provide a known input to reproducing systems. RP 90-200
23、4 Page 4 of 5 pages With a constant amplitude vs frequency sine-wave signal applied to the input of the recording system, the recorded flux vs frequency shall decrease with increasing frequency along a curve which describes the impedance of the parallel combination of a capacitance and a resistance
24、having a time constant of 70 s. The curve is the locus of the following equation: L(f) re 58.50 nWb/m = 0.132 10 log10 1 + ( 2 )2f2 dB where Lis the recorded relative short circuit flux in decibels (referred to the operating level of 58.50 nWb/m), f is the frequency in hertz for which Lis computed,
25、is a time constant of 70 s, and 0.132 is a constant calculated to make L= 0 at the reference frequency of 400 Hz. (A time constant is a shorthand notation, such as illustrated by a frequency response curve, having a shape which results from a time constant of one or more microseconds. This is a conv
26、enient way of defining a response curve and is not intended as a recommended electrical circuit.) Approximate numerical values for the frequencies employed in the test film are given in table 1. Table 1 Flux levels and relative levels vs frequency Frequency (Hz) Short circuit flux (nWb/m) Relative l
27、evel (dB) 400 31.5 40 50 80 100 160 400 1000 2500 4000 6300 8000 10000 12500 14000 16000 400 58.50 59.39 59.39 59.38 59.36 59.34 59.25 58.50 54.37 39.96 29.35 20.16 16.24 13.17 10.63 9.52 8.36 185.00 0.00 + 0.13 + 0.13 + 0.13 + 0.13 + 0.12 + 0.11 0.00 0.64 3.31 5.99 9.25 11.13 12.95 14.81 15.77 16.9
28、0 + 10.00 5.4. 2 Operating level The frequency response section is referenced to the operating level (i.e., 10 dB below reference level) to avoid possible saturation of the higher frequency signals. 5.4.3 Frequencies The 400-Hz sine-wave tones for this section shall be recorded at the operating leve
29、l of 10 dB below the 185 nWb/m reference level (i.e., at 58.50 nWb/m). The other sine-wave tones in the frequency response sequence shall be recorded at the frequencies and short-circuit flux levels specified in table 1 and defined in 5.4.1. 5.5 Reference level A 400-Hz 2% sine-wave tone shall be re
30、corded at a flux level of 185 nWb/m 10 nWb/m ( 0.5 dB) for a duration of approximately 30 seconds. RP 90-2004 Page 5 of 5 pages 6 Calibration 6.1 Flux levels 6.1.1 400-Hz reference level The reference level shall be determined by means of the calibrated short-gap ferromagnetic core reproducer techni
31、que described in ANSI S4.6. 6.1.2 Frequency response flux levels Inasmuch as the calibrated gap method of measuring short-circuit flux can only be applied to the longer wavelengths, the flux levels of other signals in the series are determined by comparing the reproduced outputs from a flat amplifie
32、r, on an ac voltmeter certified to be true-rms, or average responding rms-calibrated, and having a frequency response of 0.1 dB over a minimum frequency range of 31.5 Hz to 16 kHz. 6.2 Corrections for wide tracks When a magnetic recording is reproduced by a head that is narrower than the recorded tr
33、ack, the head collects flux in the longer wavelengths, from outside its immediate path. Thus, if in applying 6.1.2 the reproducing head is not full-width, the corrections detailed in ANSI S4.6 must be applied in order not to overestimate the flux levels for the lower frequencies. 6.3 Tolerances 6.3.
34、1 Short circuit flux levels The flux level at each frequency from 31.5 Hz through 10 kHz shall be within 0.50 dB of the value in table 1. The flux level at each frequency from 10 kHz through 16 kHz shall be within 1.0 dB of the value in table 1. Measurements shall be made as specified in 6.1.2. 6.3.
35、2 Full-width uniformity of short-circuit flux The recording shall be monitored and checked for accuracy over a 200-mil area as designated by SMPTE 97. 6.3.3 Tolerances The frequencies shall be within 2% of the values in table 1. 6.3.4 Uniformity within single-frequency test segments The reproduced level for any test segment shall not vary over the length of that segment by more than 0.5 dB, when measured with a standard volume indicator conforming to ANSI/IEEE 152.
