SMPTE ST 183M-1996 Motion-Picture Film - Photographic Audio Level Test Films - Measurement of Photoelectric Output Factor.pdf

1、SMPTE 183M 96 m 8357401 O002336 493 m SMPTE STANDARD ANSVSMPTE 183M-1996 Revision of ANCI/CMPTE 183M-1985 for Motion-Picture Film - - Photographic Audio Level Test Films M eas u re m en t of Photoelectric Output Factor “23EC Page 1 of 4 pages 1 Scope 2.3 Photoelectric output factor (PoF) 1.1 This st

2、andard specifies the method of measurement of the photoelectric output factor of single photographic audio level test films in all film gauges, using a calibrating audio repro- ducer. It is applicable to both variable-area and variable-density audio records. 1.2 The standard also specifies the inten

3、ded performance of a calibrating audio reproducer. 1.3 Calibrated audio-level test films are employed to measure the precise output level of photographic audio reproducers and the photoelectric output factor of different audio records, and to establish a reference level on a standard program-level m

4、eter appropriately chosen for the installation. 2 Definitions and symbols When reproducing an audio level test film on a calibrating reproducer, the photoelectric output factor is the ratio of the peak-to-peak output voltage from the film to the maximum output of the reproducer as defined in 2.2. 3

5、Method of measurement 3.1 Three steps shall be required to measure the photoelectric output factor: 3.1.1 Measure the maximum photoelectric out- put (MPo) of the calibrating reproducer by one of two methods - the dc method or the ac method as specified in clause 5. 3.1.2 Measure the peak-to-peak out

6、put voltage of the test film as specified in 5.2. 3.1.3 Calculate the photoelectric output factor as specified in clause 6. 2.1 Voltage outputs (VI, V2, V3, and V4) The output voltage levels (figures 1 and 2) from the calibrating audio reproducer measured at a point in the circuitry where the voltag

7、e relation- 4.1 Method ship to the amplitude of the audio record is essen- tially linear. 2.2 Maximum photoelectric output (MPo) 4 Measurement of maximum photo- electric output Either the dc method or the ac method shall be used for measuring the maximum photoelectric output of the calibrating repro

8、ducer. The voltage difference obtained between full illumina- tion of the photoreceptor by the scanning beam and complete occlusion of the scanning beam, as defined by Vi and V4 in figures 1 and 2. 4.2 Equipment 4.2.1 For both methods, a calibrating reproducer and instrumentation arranged in accorda

9、nce CAUTION NOTICE: This Standard may be revised orwithdrawn at any time. The procedures of the Standard Developer require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of publication. Purchasers of standards may receive current informatio

10、n on all standards by calling or writing the Standard Developer. Printed in USA. Copyright 0 1996 by THE SOCIETY OF - American National Standard MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hamdale Ave., Whae Plains, NY 10607 (914) 761-1100 Approved March 8,1996 SUPTE L83U 96 m 8357403 0002337 32T

11、 m ANSUSMPTE 1mM-1996 Figure 1 - Calibration waveforms - DC method “2 VI Figure 2 - Calibration waveforms - AC method with figure 3 and aligned in accordance with the appropriate audio record format document shall be required. 4.2.2 The width of the scanning beam at the film plane shall be within 1%

12、 of the nominal value specified in the appropriate audio record format document. 4.3 Additional specifications for dc method The combination of phototransducer and amplifier shall have a constant electrical peak output for all frequencies from the measuring frequency down to O Hz or dc f 1% or O. 1

13、dB. 4.4 Additional specifications for ac method 4.2.3 The uniformity of illumination across the width of the scanning beam, together with the point-to-point photon efficiency of the photo- transducer, shall be constant within f 5%. 4.4.1 The scanning beam shall be interrupted by a mechanical shutter

14、 (figure 4) that gives equal on-and-off durations at a nominally constant frequency, and has a nonreflecting black surface. Page 2 of 4 pages SMPTE 383M i6 8357403 0002338 266 ANSIISMPTE 183M-1996 FILM PLANE EXCITER LAMP ?- SLIT CELL SHUT TER WH EEL (AC METHOD ONLY 1 OSCILLOSCOPE WITH DC RESPONSE PE

15、AK READING VOLTMETER (IF REQUIRED) Figure 3 - Equipment required to establish photoelectric output factor Figure 4 - Shutter wheel 4.4.2 The frequency of interruption of the scan- ning beam shall match the frequency of the audio record on the audio level test film (+ 5%). 4.4.3 When the output of th

16、e test film is meas- ured (5.2), the shutter shall be locked open (in the full-illumination position producing voltage V4 when operating). 4.4.4 The combination of phototransducer and amplifier shall have an electrical peak output that shall not vary by more than k 5% or 0.5 dB. 5 Method of measurem

17、ent 5.1 DCmethod With no film in the reproducer, measure the output voltage with the phototransducer directly illuminated by the scanning beam and also measure the output voltage with the scanning beam completely occluded. Compute the maximum photoelectric output (Mpo) by taking the difference betwe

18、en these two voltages. 5.2 AC method With no film in the reproducer and with the shutter operating, measure the peak-to-peak amplitude of the output signal voltage using the peak reading ac volt- meter. This reading is the maximum photoelectric output (MPo) and is compared to the measurement of the

19、peak-to-peak output of the test film as measured using the peak reading ac voltmeter. 6 Calculation of the photoelectric out- put factor (PoF) Compute the photoelectric output factor of the test film by dividing the peak-to-peak amplitude of the test film as measured in 5.2 by the maximum photoelect

20、ric output of the reproducer. Page 3 of 4 pages SUPTE 383U 9b 8357403 0002339 LT2 = ANSVSMPTE 183M-1996 Annex A (informative) Additional data A.1 An ideal test film should have a photoelectric output factor of 1.0. This is a theoretical value that cannot be obtained in photographic audio recording b

21、ecause of audio track image density, fog density, base density, and track configuration limitations. A.2 Use of calculated corrections for incorrect scanning- beam width may lead to errors. A.3 A theoretically derived photoelectric output factor can be calculated for variable-area audio records usin

22、g the following equation: POF (theoretical) = TxRxM where T (transmission factor) is the difference in transmit- tance between the clear and dark areas of the audio track image, R (reduction factor) is the ratio between the maxi- mum modulated width of a variable-area audio track and the width of th

23、e reproducer scanning beam, as defined by the appropriate standards, and M (film modulation factor) is the ratio of the modulation height of the test film to the maximum modulated width of a variable-area audio track for that format. A.4 Accuracy in measuring the photoelectric output factor of an au

24、dio level test film is not significantly affected by harmonic distortion contained within the test film, providing the total harmonic distortion as measured at the output of the reproducer is not greater than 3%. A.5 A true peak-measuring voltmeter should be used for the peak-to-peak voltage measure

25、ments. Measurements made with an average or an rms-responding voltmeter corrected to give pseudo-peak values will be in error. The meter should have an accuracy of f 0.1 dB over the bandwidth from 31.5 Hz to 16 kHz. Alternately, a calibrated osciilo- scope can be used to measure the true peak-to-peak voltage. It should have the same accuracy. Page 4 of 4 pages