1、Rec. 711-1 1RECOMMENDATION 711-1SYNCHRONIZING REFERENCE SIGNALSFOR THE COMPONENT DIGITAL STUDIO(Question 25/11)(1990-1992)Rec. 711-1The CCIR,consideringa) that the definition of synchronizing reference signals for component digital studios would be of benefit in theimplementation of equipment operat
2、ing in accordance with Recommendations 601 and 656;b) that such signals should have a maximum of commonality between the 525 line and 625 line versions;c) that signals in accordance with Recommendation 656 contain in a conveniently accessible and accurate formall the information required to synchron
3、ize digital component equipment;d) that the use of digital circuitry introduces the possibility of new techniques in studio synchronization;e) that equipment in accordance with Recommendations 601 and 656 may have to operate in a mixed analogueand digital environment for a considerable period;f) tha
4、t compatibility with synchronizing reference signals for component analogue studios would be anadvantage;g) that signals generated in accordance with Recommendation 470 are widely used for synchronization in studios,recommendsthat the synchronizing reference signals for component digital equipment o
5、perating in accordance withRecommendations 601 and 656 should be as defined below:1. Synchronization method1.1 Input synchronizationInput synchronization means the synchronization of the component digital studio or equipment by an inputsignal.When synchronizing to an input signal, the equipment has
6、of necessity to derive clock and timing referenceinformation from the input video signal.1.2 Output synchronizationOutput synchronization means the synchronization of two or more signal sources.Equipment requiring a separate reference for output signals should be capable of using either a digital si
7、gnal inaccordance with Recommendation 656 or of deriving clock and timing reference information from a signal of the formdefined in Annex 1. Equipment requiring such a reference should make provision for analogue and digital signals asalternatives (see Notes 1 and 2).Note 1 In order to provide a ref
8、erence signal within the specified tolerances, it may be necessary in practice to providea timing reference generator or a synchronizing pulse generator to serve the local area.Note 2 It is appropriate to provide for the fully digital environment by allowing for the use of a digital signalconforming
9、 to Recommendation 656 as a synchronizing reference.2 Rec. 711-1ANNEX 11. IntroductionThis Annex describes an analogue reference signal for the synchronization of component digital videoequipment*.2. Analogue synchronizing reference signal2.1 Signal characteristicsThe reference signal shall be a 525
10、-line or 625-line signal as defined in Recommendation 470, appropriate tothe system, in which the active video information is replaced by blanking level*.In this application the chrominance subcarrier burst or the unmodulated subcarrier of the SECAM system areoptional.2.2 Signal amplitude and polari
11、tyThe amplitude of the synchronizing pulses shall be 300 mV nominal.The amplitude of the optional subscriber burst shall be 300 mV peak-to-peak nominal.The polarity of the synchronizing pulses shall be negative.2.3 Build-up time of line synchronizing pulsesThe build-up time of the leading (reference
12、) edge of line synchronizing pulses shall not exceed 210 ns,measured between the 10% and 90% amplitude levels.2.4 JitterThe timing of individual leading edges of line synchronizing pulses shall be within 2.5 ns of the averagetiming of leading edges, as determined over at least one field.2.5 Impedanc
13、eThe reference signal shall operate in a 75 environment.2.6 ConnectorThe connector shall conform to the standard BNC type (IEC Publication 169-8 (1978)._*Studies of broadcasting with both 525-line and 625-line standards have concluded that, to cater for a mixed analogue/digitalenvironment, satisfact
14、ory performance, flexibility and commonality are achieved by the use of the analogue black signal modifiedslightly in respect of the tolerance on rise-time and jitter.*Reference signals of higher constant average picture level (APL) are specifically not recommended because they may causeperformance
15、degradation related to APL variations between the vertical interval and other parts of the signal. Furthermore,reference signals with changing APL, such as moving video or switched test signals, are also specifically not recommendedbecause they may cause disturbances to the video signal being processed by the equipment for which they are the reference.
