1、BRITISH STANDARD BS 5550-5.4.6: 1988 ISO 8687:1987 Cinematography Part 5: Common to more than one film gauge Section 5.4 Sound Subsection 5.4.6 Method for measurement of the signal to noise ratio of8mm type S, 16mm and35mm variable area photographic sound records UDC 778.534.4:534.6BS5550-5.4.6:1988
2、 This British Standard, having been prepared under the directionof the Cinematography and Photography Standards Committee, was published underthe authority of the BoardofBSI and comes into effect on 30 December 1988 BSI 10-1999 The following BSI references relate to the work on this standard: Commit
3、tee reference CPM/5 Draft for comment 86/40170 DC ISBN 0 580 16925 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Cinematography and Photography Standards Committee (CPM/-) to Technical Committee CPM/5, upon which the following bodies
4、 were represented: Association of Cinematograph Television and Allied Technicians Association of Independent Cinemas British Broadcasting Corporation British Film and Television Producers Association British Film Institute British Kinematograph, Sound and Television Society Cinematograph Exhibitors
5、Association of Great Britain and Northern Ireland ITV Association Institute of Amateur Cinematographers Royal Photographic Society Amendments issued since publication Amd. No. Date of issue CommentsBS5550-5.4.6:1988 BSI 10-1999 i Contents Page Committees responsible Inside front cover National forew
6、ord ii 1 Scope and field of application 1 2 Reference 1 3 Definitions 1 4 Apparatus 1 5 Test track 3 6 Test measurements 4 7 Bibliography 4 Annex A Additional data 5 Figure 1 Measuring apparatus for signal-to-noise ratio 3 Figure 2 Modulation width 5 Figure 3 Sample weighting network 6 Table 1 Weigh
7、ting curve 2 Table 2 Single tone burst response 2 Table 3 Repetitive tone-burst response 3 Publications referred to Inside back coverBS5550-5.4.6:1988 ii BSI 10-1999 National foreword This Subsection of BS5550 has been prepared under the direction of the Cinematography and Photography Standards Comm
8、ittee. It is identical with ISO8687:1987 “Cinematography Signal-to-noise ratio of8mm type S,16mm and35mm variable-area photographic sound records Method of measurement” published by the International Organization for Standardization (ISO). Terminology and conventions. The text of the International S
9、tandard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Stan
10、dards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Subsection of BS5550”. There is no British Standard identical with CCIR Recommendation 468-2, but since this
11、 is referred to for information only, it does not affect the validity of this standard. CCIR Recommendation468-2 is obtainable from the Comit Consultative International des Radiocommunications, 2 Rue de Varemb, 1211 Genve 20, Switzerland. A British Standard does not purport to include all the necess
12、ary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard BS 5550 Cinematography ISO 70:1
13、981 Subsection 3.4.1:1978 Specification for position and width dimensions of35mm negative photographic sound record on35mm motion-picture film (Technically equivalent) ISO 71:1977 Subsection 2.4.1:1978 Specification for positions and dimensions of16mm negative photographic sound record on16mm, 35/16
14、mm and35/32mm motion-picture film (Identical) ISO 2939:1986 Subsection 3.2.3:1978 Specification for positions and dimensions of the picture image area and photographic sound record on35mm motion-picture release prints (Technically equivalent) ISO 4243:1979 Subsection 2.2.3:1980 Specification for pos
15、itions and dimensions of picture image area and photographic sound record on16mm motion-picture release prints (Identical) ISO 4244:1979 Subsection 1.4.5:1980 Specification for position and width dimensions of photographic sound record on8mm Type S motion-picture prints (Identical) Summary of pages
16、This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS5550-
17、5.4.6:1988 BSI 10-1999 1 1 Scope and field of application This International Standard specifies a preferred method and an alternative method for measuring the signal-to-noise ratio of8mm type S,16mm and35mm variable-area photographic sound records. 2 Reference CCIR Recommendation 468-2, Measurement
18、of audio-frequency noise in sound broadcasting, in sound-recording systems and on sound programme circuits. 3 Definitions 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 r
19、ecorder, but with 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 photo
20、graphic sound records (See clause7.) 3.3 system noise the noise output of the reproducer under running conditions with lamp on, but no film 3.4 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 ne
21、twork a circuit which alters the frequency 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 (seethe annex, cla
22、usesA.4 andA.5): a) For the preferred method, type CCIR consists of a weighting network with unity gain at1000Hz and a quasi-peak response voltmeter. The system is described in4.1.1 and is in accordance with CCIR Recommendation468-2. b) For the alternative method, type CCIR/ARM consists of a weighti
23、ng network with unity gain at2000Hz and an average responding voltmeter, calibrated to the root-mean-square response for a sine wave. The system is described in4.1.2. Type CCIR measurements should be made when the system to be measured contains significant amounts of impulse noise. The readings made
24、 on the two measuring systems are generally different and cannot be compared. The type of measurement used shall be stated when giving the result. 4.1.1 CCIR measuring apparatus An acceptable signal-to-noise measuring apparatus is shown inFigure 1 and consists of the following items. 4.1.1.1 Weighti
25、ng 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 ofTable 1. The permissible differences between the response curve of the measuring network and the nominal response of the weighting network sha
26、ll be as shown in the last column ofTable 1. A means shall be provided for bypassing or defeating the weighting network. 4.1.1.2 Voltmeter 4.1.1.2.1 Response to single tone bursts The CCIR voltmeter shall provide a voltage indication proportional to the quasi-peak value of the signal, as follows. Th
27、e meter shall respond to single tone bursts as shown inTable 2. The method of measurement shall be as follows: single bursts of5kHz tone shall be applied to the input at an amplitude so that the steady signal gives a reading of80% of full scale. The limits of reading corresponding to each duration o
28、f tone burst are given inTable 2.BS5550-5.4.6:1988 2 BSI 10-1999 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 near
29、ly constant at80% of full 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 inTable 3. The method of measurement shall be as follows: a series of5ms bursts of5kHz tone shall be applied to the input at an ampl
30、itude so that the steady signal gives a reading of80% of full scale. The limits of reading corresponding to each repetition frequency are given inTable 3. The tests shall be performed without adjustment of the attenuators but the characteristic shall be within tolerances on all ranges. 4.1.1.2.3 Ove
31、rload characteristics The overload capacity of the measuring set should be more than20dB 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 log
32、arithmic or similar stage which may be incorporated. Overload capacity shall be measured as follows: isolated5kHz tone bursts of duration0,5ms 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 sh
33、all be decreased in steps by a total of20dB while the readings are observed to check that they decrease by corresponding steps within an overall tolerance of 1dB. The test shall be repeated for each range. 4.1.1.2.4 Reversibility error The difference in reading when the polarity of an asymmetric sig
34、nal is reversed shall not be greater than0,5dB when measured as follows: isolated1ms rectangular pulses shall be applied to the input in the unweighted mode, at an amplitude giving an indication of80% of full scale. The polarity of the input signal shall be reversed and the difference in indication
35、shall be noted. 4.1.1.2.5 Overswing The reading device shall be free from excessive overswing when measured as follows: when a1kHz tone is suddenly applied to the input at an amplitude which gives a steady reading of0,775V (or0dB), the momentary excess reading shall be less than0,3dB. Table 1 Weight
36、ing curve Table 2 Single tone burst response Frequency CCIR/ARM insertion gain CCIR insertion gain Tolerance Hz dB dB dB 31,5 63,0 100,0 200,0 400,0 800,0 1000,0 2000,0 3150,0 4000,0 5000,0 6300,0 7100,0 8000,0 9000,0 10000,0 12500,0 14000,0 16000,0 20000,0 31500,0 35,5 29,5 25,4 19,4 13,4 7,5 5,6 0
37、,0 +3,4 +4,9 +6,1 +6,6 +6,4 +5,8 +4,5 +2,5 5,6 10,9 17,3 27,8 48,3 29,9 23,9 19,8 13,8 7,8 1,9 0,0 +5,6 +9,0 +10,5 +11,7 +12,2 +12,0 +11,4 +10,1 +8,1 0,0 5,3 11,7 22,2 42,7 2,00 1,40 a 1,00 0,85 a 0,70 a 0,55 a 0,50 0,50 a 0,50 a 0,50 a 0,50 0,00 0,20 a 0,40 a 0,60 a 0,80 a 1,20 a 1,40 a 1,65 a 2,00
38、 +2,80 a Z a This tolerance 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;1000;5000;6300; and20000Hz. Burst duration (ms) a 1 2 5 10 20 50 100 200 Amplitude reference steady signal reading (%) (dB
39、) 17,0 15,4 26,6 11,5 40 8,0 48 6,4 52 5,7 59 4,6 68 3,3 80 1,9 Limiting values Lower limit (%) (dB) 13,5 17,4 22,4 13,0 34 9,3 41 7,7 44 7,1 50 6,0 58 4,7 68 3,3 Upper limit (%) (dB) 21,4 13,4 31,6 10,0 46 6,6 55 5,2 60 4,4 68 3,3 78 2,2 92 0,7 a The rise- and fall-time of the burst envelope should
40、 be less than54s.BS5550-5.4.6:1988 BSI 10-1999 3 Table 3 Repetitive tone-burst response 4.1.1.2.6 Calibration Calibrate the instrument so that a steady input signal of1kHz sine wave at0,775V root-mean-square, having less than1% total harmonic distortion, gives a reading of0,775V (or0dB). The scale s
41、hall have a calibrated range of at least20dB with the indication corresponding to0,775V (or0dB) between2 and10dB below full scale. 4.1.2 CCIR/ARM measuring apparatus An acceptable signal-to-noise measuring apparatus is shown inFigure 1 and consists of the following items. 4.1.2.1 Weighting network T
42、he insertion gain of the weighting network shall vary with the frequency in accordance with the numerical values shown in the second column ofTable 1. The permissible differences between the response curve of the measuring network and the nominal response of the weighting network shall be as shown i
43、n the last column ofTable 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 responding to the average value of the rectified signal as calibrated to the root-mean-square response for a sine wave input.
44、It 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 a1kHz signal is suddenly applied to the input at an amplitude which gives a steady rea
45、ding of approximately two-thirds of full scale, the momentary excess reading shall be less than0,3dB. 4.2 Test reproducer The area of the film scanned by the test reproducer shall be as described in the applicable International Standard (see clause7) defining the dimensions of the photographic sound
46、 records. The test reproducer shall be capable of reproducing all frequencies of a multifrequency test film, as described by the applicable International Standard (see clause7), at a uniform level 2dB. If the test reproducer does not meet this criterion, the frequency response of the test reproducer
47、 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 correct method of quoting signal-to-noise ratio is
48、to state the measurement bandwidth and the response of the reproducer within this bandwidth. 5 Test track The test track shall consist of three sections, recorded in sequence at the same lamp-current setting and printed at the same light step. 5.1 Section 1 shall consist of a sound record of1000Hz r
49、ecorded at80% of full modulation and shall serve as the reference signal. The length of this section shall provide a running time of approximately10s. When reproduced, this section shall have a harmonic distortion of less than5%. 5.2 Section 2 shall be recorded with an unbiased, unmodulated sound record. The length of this section shall provide a running time of approximately15s. 5.3 Section 3 shall be recorded with a biased, unmodulated sound record. The length
