ITU-R BT 1204-1995 Measuring Methods for Digital Video Equipment with Analogue Input Output《带有模拟输入 输出的数字视频设备的测量方法》.pdf
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1、226 Rec. ITU-R BT.1204 RECOMMENDATION ITU-R BT. 1204 MEASURING METHODS FOR DIGITAL VIDEO EQUIPMENT WITH ANALOGUE INPUT/OUTPUT (Question i73J-R 63/1 i) (1995) The ITU Radiocommunication Assembly, considering 4 that analogue/digital conversion processes will continue even in “totally-digitai studio sy
2、stems; b) with analogue input/output; that there is the problem of instability in measuring the analogue characteristics of digital video equipment c) analogue input/output; that stable measuring methods are essential for improving the performance of digital video equipment with d) that it is desira
3、ble that such measuring methods should make use of existing instruments as much as possible; e) that the dithering method is effective for randomizing the quantization errors; 0 that a shallow-ramp signai is a suitable test signal to measure signal-to-noise ratio, recommends 1 input/output based on
4、525-line or 625-line systems. that the measuring method described in Annex 1 should be used for digital video equipment with analogue 1 Introduction This Recommendation is intended to assist in measuring the characteristics of studio digital video equipment with analogue input/output. When measuring
5、 analogue characteristics such as signal-to-noise ratio (SIN), differential gaidphase (DGDP), and the luminance non-linearity of the equipment, the quantization error of the coding process causes variations in the results of the measurement. Considering the SIN of 8-bit video equipment, for example,
6、 the measured SIN shows some number within 50 dE3 and 70 dB when using a conventional method with a noise meter. To solve these problems, the Broadcasting Technology Association of Japan (BTA), has organized a Working Group to study new measurement methods for digital video equipment with analogue i
7、nput/output. Similar work has been carried out in the United Kingdom. The approach described in the Recommendation provides stable measuring results using the following methods to avoid quantization errors: - superimposing a dither signai on a test signal, and removing the dither signal prior to the
8、 measurement with frequency band limitation filters; and - using a shallow-ramp signal instead of a flat signal for an SIN measurement to make the test signal cross the quantizing levels as much as possible. Measurement items described in the Recommendation are SlN, DGDP, pulse characteristics and l
9、uminance non-linearity (see Note 1). Although the Recommendation addresses measuring methods for equipment of 525-line and 625-line systems, the concept of the methods is applicable to other systems such as HDTV and EDTV. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicens
10、ed by Information Handling ServicesRec. ITU-R BT.1204 227 NOTE 1 - Gairfrequency characteristics are important in specifying the performance of television equipment. However, a sped measuring instrument with an averaging function is required to remove the dither signai, so the measuring method for g
11、airfrequency characteristics is described in Appendix 1. 2 General definitions 2.1 Video equipment and test signais The video equipment and test signals are based on 525-line systems or 625-line systems. 2.2 DUT DUT stands for a device under test, namely, a piece of video equipment being measured. T
12、he AID or D/A conversion in DUTs to be measured using the recommended methods should have a resolution of 8 bits or more. 2.3 IREunits An IRE unit is a linear scale for measuring the relative amplitudes of a television signal with a zero reference at blanking level. 100 IRE units correspond to the r
13、eference white level, and -40 IRE units correspond to the bottom of the synchronization pulses. 525-line systems are often operated with 100 IRE units = 0.714 V p-p, while 625-line systems are often operated with 100 IRE units = 0.7 V p-p. 2.4 Video analyser In this Recommendation, the video analyse
14、r is defined as an automatic video signal measuring instrument which has the functions to average and interpolate the signais to reduce the noise components of the measured signals. 3 The defiiition of dither signal 3.1 Dither signai A dither signal is used to stabilize measured values by causing ve
15、ry srnail random changes to the level of test signals and thus dispersing quantization errors evenly in relation to the quantization levels. Since it is necessary to remove the dither signai easily before measuring, in this Recommendation a sine-wave signal is used as a dither signai, which can be r
16、emoved with a simple filter. The sine-wave signal should be asynchronous (non-locked) with the test signal in order to work as a dither signal. The frequency of the sine-wave signal for this purpose should preferably be outside the nominal cut-off frequency of the system, but within the bandwidth of
17、 the AID and D/A converter of the DUT. For the 525-line system, it is recommended to use a frequency of 5.162 MHz which is the second-null point of a 4.2 MHz low pass filter (LPF) in a video noise meter, and for the 625-line system, to use a frequency of 6.145 MHz which is the null-point of 5.0 MHz
18、LPF. This assumes that DUTs are operating at a sampling frequency significantly greater than twice the highest frequency of the noise measurement filters; for example, at a sampling frequency of four times colour subcarrier frequency as in SMPTE 244 format for composite signals and 13.5 MHz as in Re
19、commendation ITU-R BT.601 for component signals. The amplitude of the sine-wave signai should be 30 mV p-p f 10%. It is desirable that the sine-wave signal is superimposed during the active period of the test video signal. 3.2 Notes 3.2.1 Superimposing the dither signal Superimposing the dither sign
20、al onto a test signal can be realized by the circuits shown in Fig. 1. 1TU-R RECMN*BT. 1204 75 m 4855212 O526101 205 m COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services228 Rec. ITU-R BT.1204 FIGURE 1 Example ciraiis for superimposing th
21、e dither signal 5.162-6.145 MHz sine wave generator gate input A i Blanking signai a) Normal supairriposer 3.64 V pp 5.162-6.145 MHz 4.5 ksL sine wave generator gate input I Blanking signal I Test signai generator El- b) Simple superimposer Note I -The amplitude of test signais may decrease after pa
22、ssing through this circuit. mr ; 3.2.2 When measuring a DUT using the dither signal, it is necessary to observe and measure the DUTs output waveform after removing the dither signal. The dither signal using a non-locked sine-wave signal can be removed by the following methods: - by using band-limiti
23、ng filters; - - The latter two methods are effective but require special measuring instruments. a) Video signal measuring instruments incorporate various types of filters for easy and accurate measurements. These filters are efficient in removing the dither signal if it has a relatively high frequen
24、cy such as 5.162 MHz for 525-line systems and 6.145 MHz for 625-line systems. Removing the dither signai before measurements by means of averaging with the video analyser; by cancelling with an operational amplifier. Dither removal using band-limiting filters ITU-R RECMN*BT= 1204 95 D 4855212 052bl1
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