1、SHPTE RECOMMENDED PRACTICE RP 45-1972 Use am! Gre of Sound TUL Films 1. Scope 1.1 This recommended practice describes the proper method for use of sound test films, the reliability of the conclusions to be drawn from their output, the precautions necessary for reasonable accuracy, and the proper sto
2、rage for preservation of Cali- bration. 1.2 Thia recommended practice is intended to apply to ali sound test films, some of which bear a pho- tographic recording and some a magnetic record- ing. 2. Preparation for Reproduction 2.1 Prior to running a test lm, it is desirable to make the following che
3、cks on the transport: 2.1.1 The transport should be clean, particularly at all film contact points of the film path and its asso- ciated devices, and at any optical or magnetic scanning point. 2.1.2 The mechanical alignment should be checked so that the film is properly transported and guided, and s
4、o that distortions of the web do not 2.1.3 Proper supply and take-up reels should be pro- vided, true and undamaged, free from burrs and other defects, properly aligned and seated on their spindles, and with the largest practical hub diameter, in ail cases at least equal to the mini- mum recommended
5、 for the test film. 2.2 Prior to running any magnetic test film, the mag- netic heads should be demagnetized. The entire film path should be checked for residual mag- netism and demagnetized as needed. 2.3 Each test film should be examined for possible physical distortion at the time of use. If dis-
6、 torted, its reliability is questionable. 2.4 Each test film should be examined for dirt and, if obvious, should be cleaned before use. A photo- graphic test film can be cleaned with any good motion-picture film cleaner. A magnetic test film can be cleaned only with a magnetic tape cleaner. occur. P
7、age 1 of 4 pages 2.5 Sound test lms should be run in the sequence recommended herein for the initial setup of a machine. A test film presupposes that the prior adjustments have been verified, and that the re- sults may not conform to the intent of the calibra- tion if this is not valid. 2.5.1 Proper
8、 widthwise alignment of the scanning 2.5.2 Azimuth coincidence 2.5.3 Flutter 2.5.4 Amplifier gain adjustment for individual tracks and amplifier gain adjustment and balance for multiple tracks 2.5.5 Frequency response beam or magnetic gap 3. Accuracy of Test Films 3.1 Quantitative test films are int
9、ended to be evalu- ated on reproduction by objective instruments whose reading provide a figure of merit by which equipment performance can be described and rated. If adjustment of performance is intended to fallow evaluation, the readings from the re- production of quantitative test films indicate
10、the magnitude of such adjustments or corrections. 3.2 Test films in manufacture usualiy are calibrated to a level of accuracy higher than that common to the equipment they are intended to check. 3.2.1 Test lm transports with associated equipment and instrumentation are of laboratoryreference quality
11、. 3.2.2 The calibration limits of test films when released are shown in the appropriate standard or parent document. 3.3 Test films generally are reproduced and used for the evaluation of equipment that is of commercial quality. 3.4 Test films in the field and evaluated by reproduc- tion in the over
12、ail system may appear to have greater variability or uncertainty than the initial calibration shows. Copyright 1972, by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 9 East 4Ist Street, New York, N.Y. 10017, (212) TN 7-5410 Approved April 1972 SMPTE RP*45 72 m 8357401 0000492 180 m Page 2 o
13、f 4 pages 3.4.1 Although test films are made as precisely as pos- sible, there are uncertainties in measurement that limit accuracy of performance in the field. Some equipment even may indicate relative dif- ferences among test films that appeared identi- cal on the moqe precisely defined calibratio
14、n equipment. 3.4.2 The limits of repeatability of a test film run on one system at various times, or on several systems consecutively, cannot be predicted quantitatively without careful study. These isolated values are also less meaningful than the record of trends recommended in Section 3.5. Freque
15、ntly, the observed “normal” variability is about twice the specified limits of accuracy in the original cali- bration. 3.4.3 Improper storage and/or the introduction of dirt and physical defects will further increase the probable error. 3.5 Equipment performance trends measured by test films are fre
16、quently more significant than in- dividual readings, and become essential if close control is required. 3.5. It is recommended that for each piece of equip- ment to be examined, a chart or table be kept of the results obtained at each pass of a par- ticular test film. The test film serial number, th
17、e date and time, and the conditions of the run should be noted. This definitive record of trends is essential if close control of performance and intelligent maintenance are to be achieved. 3.5.2 When possible, two copies of each test film should be on hand, one used frequently and a second used inf
18、requently and stored in a dif- ferent location. 3.5.3 The two copies should be reproduced in consecu- tive playback on some suitable schedule for oc- casional direct intercomparison. 3.5.4 When the frequently used test film becomes worn out, the less frequently used one should take its place, and a
19、new film introduced into the backup position. 3.5.5 Trends observed in the results from both test films identify equipment problems. Trends ob- served in the results from only one film indicate test film problems. 3.5.6 The scatter of the data is a measure of the re- peatability of measurement under
20、 actual oper- ating conditions. 4. Subjective Test Film 4.1 Certain sound test films are intended for normal listening evaluation rather than for quantitative measurement. 4.2 When the test film contains program material or other selections designed for subjective evaluation to establish whether a s
21、ystem is adequate and pleasing, the reproduction must be in an environ- ment as specified by the instructions. The acoustic characteristics of the listening area must not dis- RP 45-1972 tort the program material in an unanticipated way, thereby giving a false impression of system performance as it
22、is normally operated. 4.3 When the purpose of reproducing the test film is to alter the response of a system in order to com- pensate for the deficiencies of the loudspeaker or of the listening environment, it must be recog- nized that this system no longer can be compared with other systems in any
23、simple manner. 5. Storage of Test Films 5.1 Two storage requirements can be distinguished: the storage of test films in intermittent use, for periods of a few days to perhaps a month between runnings, and the storage of test films for longer periods (to serve as teferences and arbiters in examining
24、long-term performance of equipment or films). The basic precautions are the same, but it will be obvious that certain of these precautions should be applied prudently to all storage, and that others become most significant when the storage period is long. 5.2 5.2. Preparation of Test Films for Inter
25、im Storage Estimate whether the test film has been dried to excessively low humidities such as 10 percent or lower (by use in a very dry environment, or by subjection to projection in an intense radiant beam, etc.), or whether it has been moistened by excessively high humidities such as 80 percent o
26、r above (as by use in a humid environment, or in a comfort-conditioned area that does not reduce the moisture significantly below the dew point, etc.) , If either is the case, allow the film to equilibrate in an environment known to be be- tween 20 and GO percent relative humidity, as a very loosely
27、-wound roll with open spaces be- tween all convolutions, for G to 16 hours. The film should then be wound as specified in Sec. 5.2.4. The rather wide humidity tolerance of film permits the use of a low-cost desk- or home- type indicator for determining relative humidity. 5.2.2 Select a good reel for
28、 storage: true, free of de- fects, and with a hub diameter at least equal to the minimum recommended. 5.2.3 Films in storage should be wound tail out. If the take-up reel used in normal operation is not suitable for storage, two rewindings will be nec- essary to put the film in preferred configurati
29、on. 5.2.4 Wind the film onto the reel so that the roll is firm but not rigid, and such that the alignment of convolutions is good and the sidewall of the wound roll does not show protruding convolu- tions. Fasten the outside end of the film in place with a nonbleeding, pressure-sensitive tape. 5.2.5
30、 Enclose the film in ametal or impermeable plastic can. If storage is to be for more than one or two weeks, tape the can closure. 5.2.6 The film should be rewound immediately before use to put it in head-out orientation. Paga 3 of 4 pages SMPTE RP*45 72 8357403 0000493 037 W RP 42-1972 5.3 Protectio
31、n of Film During Interim Storage 5.3.1 Test films should be stored where the tempera- ture will not go above 80F (27C). Lower tem- peratures are preferred. 5.3.1.1 If test films are stored below 60F (16OC), the film should be ailowed to warm up in the un- opened can until it has substantialIy reache
32、d the temperature of the test area. 5.3.2 Ail test films in an unsealed container should be protected from exposure to acidic, corrosive, or reactive gases or vapors. 5.3.3 Magnetic test 6lms should be stored as far as possible from magnetic fields associated with motors, transformers, etc., and nev
33、er closer than five feet to such equipment. Fields not in excess of four times the earths magnetic field may be assumed safe even for extended storage. 5.4 Preparation of Test Films for Extended Storage 5.4.1 The equilibrium relative humidity of the test film during storage should be as follows (See
34、 Sec. 9 (a) ) : 5.4.1.1 Cellulose ester base films, 15-30 percent rela- tive humidity for dye images, 15-20 percent relative humidity for silver images and mag- netic films. 5.4.1.2 Polyester base films, 25-30 percent relative humidity for dye images, 25-50 percent rela- tive humidity for silver ima
35、ges and magnetic films. 5.4.2 The storage temperature should be below 60F (16”C), and preferably below 35F (2C) for dye images. A storage temperature below 70F (21C) is satisfactory for silver images and mag- netic films. Film may be safely stored at tem- peratures below freezing. 5.4.2.1 When test
36、films are removed from low-tempera- ture storage and brought into a room whose dew point is above that of the package, mois- ture will condense upon the container. The sealed package should be allowed to come es- sentially to room temperature before opening, to avoid such condensation upon the film.
37、 A 16mm roll in a taped can, set on edge, will warm up from 35F (2C) to a safe room tem- perature in 1-2 hours; a 35mm roll in 5-7 hours. 6. Protection from Physical Deformation 6.1 Ail test films depend for reliable performance upon the films being straight and true, free of differential size chang
38、es that force it out of a coherent plane. Test films when certified have such near perfection. Distortions may be intro- duced into the film from stresses producing plastic flow, and from the gain or loss of volatile com- ponents. 6.2 Physical Stresses Producing Plastic Flow 6.2.1 The deformation th
39、resholds for plastic materials such as motion-picture films are greatly depend- ent upon time. The yield point stress, beyond which nonelastic and irrecoverable deformation occurs, will be nearly as high as the break stress for suddenly applied shock loads, and may be nearly zero for stresses mainta
40、ined over a period of years. The relative importance of potentially deforming stresses, therefore, depends upon both the magnitude of each stress and the time over which it continues to act. 6.2.2 Misalignment of the film path introduces un- balanced stresses. 6.2.3 Films handled at high tensions ov
41、er rollers and other components, particularly over relieved roll- ers, guides, etc., may have the edges stretched to become longer than the mid-line. 6.2.4 Untrue and distorted flanges may pick at the edges of the test film and produce localized stretching. 6.2.5 Films wound to small diameters and h
42、eld for a time acquire an excessive elongation of the outer- most surface with respect to the innermost of each convolution, which in later use transposes to a higher than normal curl level. 6.2.6 Films wound on noncylindrical cores, or wound so that the convolutions are not essentially cylin- drica
43、l, and held for a time, develop localized “sets” that position differently in reproduction. 6.3 Gain or Loss of Volatile Components 6.3.1 The temporary gain or loss of moisture by inter- change with the environment will increase or decrease the dimensions of the film correspond- ingly. 6.3.2 Sustain
44、ed dimensional differentials, as by the subjecting of a tightly wound roll to a relative humidity gradient such that the exposed edges of the film will condition rapidly while the cen- terline may require weeks to interchange mois- ture by diffusion, will induce plastic flow. 6.3.3 The irreversible
45、loss of solvents, plasticizers, and other film constituents will reduce the film di- mensions and may induce distortion. Such loss is retarded by storage in sealed containers. 6.4 Films manufactured with internal strains may change dimension and shape on extended storage from the gradual release of
46、such strains. 7. Photographic Image Stability Test films in which a photographic image is significant, as in photographic sound test films, should be pro- tected from changes in the optical parameters of the image. The important effects and their control have been described for silver images by J. M
47、. Calhoun and for dye images by P. Z. Adelstein et al (See Sec. 9) . Common factors which may affect image stability are: (a) Residues of processing chemicals (b) Noxious or acidic gases (c) Continued exposure to high light levels (d) High relative humidity (e) High temperature Page 4 of 4 pages SMP
48、TE RPM45 72 m 83571.103 0000494 T53 I RP 45-1972 8. Magnetic Record StabiZity 8.1 Test films in which a magnetic record is significant should be protected from alteration of the mag- netic state. The important effects have been de- scribed by W. K. Grimwood et al (See Sec. 9 (c) ) . 8.2 Short wavele
49、ngth recordings are the most easily aitered, and frequency-response test films may show the most significant changes with use. 8.3 Magnetic fields may disrupt recorded information. 8.3.1 Use on a transport with magnetized heads or with bias leakage or with magnetized objects along and in proximity to the, film path. 8.3.2 Storage in an area permeated by a significant magnetic field, as in proximity to electrical power equipment facilities (See Sec. 5.8.3). 8.4 Excessive mechanical flexture may bring about a reduction in the amplitudes of short wavelength recordings. 8.5 Temper
