1、STD-SMPTE RP 47-ENGL 1779 I 8357403 0003592 833 SMPTE RECOMMENDED PRACTICE Electronic Method of Dropout Detection and Counting RP 47-1 999 Revision of RP 47-1994 I 1 Scope This practice specifies the method of electronic drop- out detection and counting for 2-in quadruplex video magnetic tape record
2、ings made in accordance with practice HB of SMPTE RP 6. 2 Dropout definition A momentary random reduction of the recovered frequency modulated (rf) playback signal that is suffi- cient to cause a substantial impairment in the video output signal of a quadruplex video tape recorder. 3 Specifications
3、The dropout to be detected shall have an rf signal reduction of 16 dB or more for 5 ps or longer. 4 Detection 4.1 Recorder alignment 4.1.1 The tip penetration shall be 2 mils for record and playback. (This penetration may not correspond to that specified in SMPTE RP 11, and adjustment of vacuum guid
4、e position may be necessary.) 4.1.2 The tip projection shall be between 1.5 mils and 2.5 mils (see annex A.l). Page 1 of 2 pages 4.1.3 Equalization shall be in accord with practice HB of SMPTE RP 6, producing a flat input-to-output response. 4.1.4 The recovered playback signal prior to limiting shal
5、l not vary more than 2 dB over four head passes, including amplitude variations due to geometrical error. 4.2 Test signal Any test signal may be used; color bars or sync and set up are preferred (see annex A.2). 4.3 Electronic dropout counter The dropout counter shall be capable of utilizing the abo
6、ve-mentioned signals and specifica- tions. 4.4 Operation The dropout counter shall be interfaced into the playback system of the video recorder so that a standard amplitude of the unlimited rf signal can be applied to the level detector of the dropout counter. This point is usually the video head sw
7、itcher output. Copyright O 1999 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (914) 761-1100 Approved April 22, 1999 Annex A (informative) Additional data A.l The range of tip projection from 1.5 mils to 2.5 mils A.3 A detailed report by the
8、SMPTE Tapes and Reels permits versatility in the heads used for dropout testing and Subcommittee is presented in Dropout considerations in is adequate in most cases. For the highest degree of repeat- video tape recordings and proposed recommended ability, heads with a tip projection of 2.0 mils to 2
9、.2 mils practices. Journal of the SMPTE, 81: 401-403, May should be used. 1972. A.2 For dropout evaluation, the sync and set up signal gives the best repeatability and minimizes machine-to-machine variables. Annex 6 (informative) Bibliography SMPTE RP 6-1994 (R1999), Recorded Carrier Frequencies and Preemphasis Characteristics for 2-in Quadruplex Video Magnetic Tape Recording for 525-Line160-Field Television Systems SMPTE RP 11-1994 (R1999), Tape Vacuum Guide Con- figuration and Position for Quadruplex Video Magnetic Tape Recording Page 2 of 2 pages
