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1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXAYHAPOAHAFI OPrAHM3AMR I-IO CTAHAPTM3AMM Cinematography - Signal-to-noise ratio of 8 mm type S, 16 mm and 35 mm variable-area photographic Sound records - Method of measurement Cinem
2、a tographie - Rapport signal/bruit des enregistrements sonores photographiques A surface variable de films 8 mm type S, 16 mm et 35 mm - Methode de mesurage ISO 8687 First edition 1987-08-0 1 Reference number ISO 8687 : 1987 (E) Copyright International Organization for Standardization Provided by IH
3、S under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:05:17 MDTNo reproduction or networking permitted without license from IHS -,-,- Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards bodi
4、es (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Esch member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations
5、, govern- mental and non-governmental, in liaison with ISO, also take patt in the work. Draft International Standards adopted by the technical co.mmittees are circulated to the member bodies for approval beforetheir acceptance as International Standards by the ISO Council. They are approved in accor
6、dance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 8637 was prepared by Technical Committee ISO/TC 36, Cinema tograph y. Users should note that all International Standards undergo revision from time to time and that any reference made h
7、erein to any other International Standard implies its latest edition, unless otherwise stated. 0 International Organkation for Standardkation, 1987 Printed in Switzerland Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards
8、 1/9972545001 Not for Resale, 04/26/2007 21:05:17 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO8687:1987 (E) Cinematography - Signal-to-noise ratio of 8 mm type S, 16 mm and 35 mm variable-area photographic Sound records - Method of measurement
9、1 Scope and field of application This International Standard specifies a preferred method and an alternative method for measuring the signal-to-noise ratio of 8 mm type S, 16 mm and 35 mm variable-area photographic Sound records. 2 Reference CCIR Recommendation 468-2, Measurement of audio- frequenc
10、y noise in Sound broadcasting, in sound-recording Systems and on Sound Programme circuits. 3 Def initions For the purpose of this International Standard the following definitions apply. 3.1 biased, unmodulated Sound record : A Sound record made with no input to the photographic Sound recorder, but w
11、ith noise-reduction biasing used in conjunction with normal practice for the recorder being used. 3.2 fully modulated Sound record : A Sound record which has an amplitude equal to the maximum amplitude permitted by the applicable International Standard defining the dimensions of the photographic Sou
12、nd records. (See clause 7.) 3.3 System noise : The noise output of the reproducer under running conditions with lamp on, but no film. 34 unbiased, unmodulated Sound record : A Sound record made with no input to the photographic Sound recorder and with no noise reduction biasing. 3.5 weighting networ
13、k : A circuit which alters the fre- quency response of the measuring apparatus by a prescribed amount to provide agreement between the measured signal-to- noise ratio and the subjective impression of noise. 4 Apparatus 4.1 Measuring devices Two types of measuring devices may be used (sec the annex,
14、clauses A.4 and A.5) : a) For the preferred method, type CCIR consists of a weighting network with unity gain at 1 000 Hz and a quasi- peak response Voltmeter. The System is described in 4.1 .l and is in accordance with CCIR Recommendation 468-2. b) For the alternative method, type CCIR/ARM consists
15、 of a weighting network with unity gain at 2 000 Hz and an average responding Voltmeter, calibrated to the root-mean- Square response for a sine wave. The System is described in 4.1.2. Type CCIR measurements should be made when the System to be measured contains significant amounts of impulse noise.
16、 The readings made on the two measuring Systems are generally different and cannot be compared. The type of measurement used shall be stated when giving the result. 4.1 .l CCIR measuring apparatus An acceptable signal-to-noise measuring apparatus is shown in figure 1 and consists of the following it
17、ems. 4.1.1.1 Weighting network The insertion gain of the CCIR weighting network shall vary with the frequency in accordance with the numerical values shown in the third column of table 1. The permissible differentes between the response curve of the measuring network and the nominal response of the
18、weighting network shall be as shown in the last column of table 1. A means shall be provided for bypassing or defeating the weighting network. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale
19、, 04/26/2007 21:05:17 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 8687 : 1987 (E) 4.1.1.2 Voltmeter 4.1.1.2.1 Response to Single tone bursts The CCIR Voltmeter shall provide a voltage indication propor- tional to the quasi-peak value of the Signal, as follows. The m
20、eter shall respond to Single tone bursts as shown in table 2. The method of measurement shall be as follows : Single bursts of 5 kHz tone shall be applied to the input at an amplitude so that the steady Signal gives a reading of 80 % of full scale. The limits of reading corresponding to each duratio
21、n of tone burst are given in table 2. The tests shall be performed both without adjustment of the attenuators with the readings being observed directly from the instrument scale, and also with the attenuators adjusted for each burst duration to maintain the reading as nearly constant at 80 % of full
22、.scale as the attenuator Steps permit. 4.1.1.2.2 Response to repetitive tone bursts The meter shall respond to repetitive tone bursts as shown in table 3. The method of measurement shall be as follows : a series of 5 ms bursts of 5 kHz tone shall be applied to the input at an amplitude so that the s
23、teady Signal gives a reading of 80 % of full scale. The limits of reading corresponding to each repetition frequency are given in table 3. The tests shall be petformed without adjustment of the attenuators but the characteristic shall be within tolerantes on all ranges. 4.1 .I .2.3 Overload characte
24、ristics The overload capacity of the measuring set should be more than 20 dB with respect to the maximum indication of the scale at all settings of the attenuators. The term “overload capacity” refers to both the absence of clipping in linear stages and to retention of the law of any logarithmic or
25、similar Stage which may be incorporated. Overload capacity shall be measured as follows : isolated 5 kHz tone bursts of duration 0,5 ms shall be applied to the input at an amplitude giving full-scale reading using the most sensitive range of the instrument. The amplitude of the tone bursts shall be
26、decreased in Steps by a total of 20 dB while the readings are observed to check that they decrease by corresponding Steps within an Overall tolerante of f: 1 d. The test shall be repeated for each range. 4.1 .I .2.4 Reversibility error The differente in reading when the polarity of an asymmetric Sig
27、nal is reversed shall not be greater than 0,5 dB when measured as follows : isolated 1 ms rectangular pulses shall be applied to the input in the unweighted mode, at an amplitude giving an indication of 80 % of full scale. The polarity of the input Signal shall be reversed and the differente in indi
28、cation shall be noted. 4.1.1.2.5 Overswing The reading device shall be free from excessive overswing when measured as follows : when a 1 kHz tone is suddenly ap- plied to the input at an amplitude which gives a steady reading of 0,775 V (or 0 dB), the momentary excess reading shall be less than 0,3
29、dB. Table 1 - Weighting curve Frequency CCIR/ARM CCIR insertion gain insertion gain Tolerante Hz dB d d 31,5 - 35,5 - 29,9 + 2,00 63,0 - 29,5 - 23,9 + 1,40* 100,O - 25,4 - 19,8 f l,oo 200,o - 19,4 - 13,8 Zl: 0,85* 400,o - 13,4 - 7,8 * 0,70* 8oao - 7,5 - 1,9 * 0,55* 1 ooo,o - 5,6 w I!I 0,50 2 ooo,o o
30、,o + 5,6 + 0,50* 3 150,o + 3,4 + 9,0 * 0,50* 4 ooo,o + 4,9 + 10,5 I!I 0,50* 5 ooo,o + 6,l + ll,7 Ik 0,50 . 6 300,O + 6,6 + 12,2 o,m 7 100,0 + 6,4 + 12,0 f 0,20* 8 000,O + 5,8 + 11,4 lt 0,40* 9 ooo,o + 4,5 + 10,l dz 0,60* 10 000,o + 2,5 + 8,l k 0,80* 12 500,o - 5,6 o,o + 1,20* 14 000,o - 10,9 - 5,3 f
31、: 1,40* 16 000,O - 17,3 - ll,7 I!I 1,65* 20 ooo,o - 27,8 - 22,2 f 2,00 31 500,o - 48,3 - 42,7 + 2,80* -00 * This tolerante is obtained by linear interpolation on a logarithmic graph on the basis of values specified for the frequencies used to define the mask, i.e. 31,5; 100; 1 000; 5 000; 6 300; and
32、 20 000 Hz. Table 2 - Single tone burst response Burst duration (ms)” 1 2 5 10 20 50 100 200 r Amplitude reference (%) 17,0 26,6 40 48 52 59 68 80 steady Signal reading (dB) - 15,4 - 11,5 - 8,0 - 6,4 - 5,7 - 4,6 - 3,3 - 1,9 Limiting values Lower limit (%) 13,5 22,4 34 41 44 50 58 68 kW - l7,4 - 13,0
33、 - 93 - 7,7 - , 7,l - 6,0 - 4,7 - 3,3 + Upper limit (%) 21,4 31,6 46 55 60 68 78 92 MB) - 13,4 - 10,o - 6,6 - 5,2 - 4,4 - 3,3 - 2,2 - 0,7 * The rise- and fall-time of the burst envelope should be less than 5 ps. 2 Copyright International Organization for Standardization Provided by IHS under license
34、 with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:05:17 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 8687 : 1987 (E) Table 3 - Repetitive tone-burst response Limiting values Lower limit Upper limit (%) 43 tdB) - 7,3 1%) 53 (db) -
35、5,5 10 100 n * 97 - 2,3 - 0,25 + 72 94 - 2,9 - 0,5 82 100 - 1,7 - 0,o 4.1 .I .2.6 Calibration Calibrate the instrument so that a steady input Signal of 1 kHz sine wave at 0,775 V root-mean-Square, having less than 1 % total harmonic distortion, gives a reading of 0,775 V (or 0 dBL The scale shall ha
36、ve a calibrated range of at least 20 d with the indication corresponding to 0,775 V (or 0 dB) between 2 and 10 d below full scale. 4.1.2 CCIR/ARM measuring apparatus An acceptable signal-to-noise measuring apparatus is shown in figure 1 and consists of the following items. 4.1.2.1 Weighting network
37、The insertion gain of the weighting network shall vary with the frequency in accordance with the numerical values shown in the second column of table 1. The permissible differentes between the response curve of the measuring network and the nominal response of the weighting network shall be as shown
38、 in the last column of table 1. A means shall be provided for bypassing or defeating the weighting network. 4.1.2.2 Voltmeter The CCIR/ARM Voltmeter shall provide an indication respond- ing to the average value of the rectified Signal as calibrated to the root-mean-Square response for a sine wave in
39、put. lt shall have sufficient sensitivity so that the noise Signals will Cause a meter deflection of at least one-third of full scale. The Voltmeter shall be free from excessive overswing when measured as follows : when a 1 kHz Signal is suddenly applied to the input at an amplitude which gives a st
40、eady reading of ap- proximately two-thirds of full scale, the momentary excess reading shall be less than 0,3 dB. 4.2 Test reproducer The area of the film scanned by the test reproducer shall be as described in the applicable International Standard (see clause 7) defining the dimensions of the photo
41、graphic Sound records. The test reproducer shall be capable of reproducing all frequen- cies of a multifrequency testfilm, as described by the applicable International Standard (see clause 7), at a uniform level k 2 dB. If the test reproducer does not meet this criterion, the frequency response of t
42、he test reproducer shall be reported along with the signal-to-noise ratios. The meter used for measuring the frequency response of the reproducer shall have no weighting network and shall have either an average response or a true root-mean-Square meter response. The cor- rect method of quoting signa
43、l-to-noise ratio is to state the measurement bandwidth and the response of the reproducer within this bandwidth. ? Weighting network VOltmeter Figure 1 - Measuring apparatus for signal-to-noise ratio Copyright International Organization for Standardization Provided by IHS under license with ISO Lice
44、nsee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 21:05:17 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 8687 : 1987 (EI 5 Test track The test track shall consist of three sections, recorded in se- quence at the same lamp-current setting and printe
45、d at the same light Step. 5.1 Section one shall consist of a Sound record of 1 000 Hz recorded at 80 % of full modulation and shall serve as the reference Signal. The length of this section shall provide a run- ning time of approximately 10 s. When reproduced, this section shall have a harmonic dist
46、ortion of less than 5 %. 5.2 Section two shall be recorded with an unbiased, unmodulated Sound record. The length of this section shall provide a running time of approximately 15 s. 5.3 Section three shall be recorded with a biased, unmodulated Sound record. The length of this section shall provide
47、a running time of approximately 15 s. 6 Test measurements 6.1 Record and develop the test track described in clause 5 under the Standard conditions for the System being checked. Provide sufficient unspliced film ahead of the test track to per- mit stabilization of the Printer Speed. 6.2 Reproduce th
48、e test track and measure the output of the reproducer preamplifier with the required test apparatus (see clause 4). Measure the Signal level of section one (the reference Signal) (see the annex, clause A.l), without the weighting net- work, then measure the Signal level of sections two and three wit
49、h the weighting network. Calculate the unbiased, unmodulated signal-to-noise ratio (A), in decibels, using the formula A 5 = 20 Ig - + 2 V2 where is the Signal level, in Volts, of section one; V2 is the Signal level, in Volts, of section two. Calculate the biased, unmodulated signal-to-noise ratio (B), in decibels, using the formula B b = 20 Ig - + 2 V3 where VI is the Signal level, in