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Tape speed determining apparatus for video signal reproducing apparatus
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Inventors: Doutsubo, Nobuhide;
Assignee: Sanyo Electric Co., Ltd. (Osaka, JP)
Primary Examiner: Faber; Alan
Assistant Examiner:
Attorney, Agent or Firm: Armstrong, Nikaido, Marmelstein & Kubovcik
A tape speed determining apparatus applied to a video signal reproducing apparatus employing a helical scanning system, a rotating head system and a pilot signal system serves to determine automatically the recording mode of a video tape to be reproduced, in case where two kinds of recording modes, i.e. a standard recording mode and a long recording mode, are applicable and the speed of a video tape differs dependently on the respective recording modes. The tape speed determining apparatus delays by an infinitesimal time "t" the timing for selection of the reference signals f.sub.1 and f.sub.3 out of the reference signal f.sub.1 to f.sub.4 supplied at the time of reproduction, as compared with the reproducing head selection timing. An error signal generated during this delayed time "t" is sampled and held for a frame period. A wavelength of a fundamental wave of the sampling output is determined by counting the number of capstan rotation detecting pulses, and thus the recording mode of the video tape is determined as a function of the count value. |
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DETAILED DESCRIPTION The present invention makes, it possible to overcome all of such disadvantages of the apparatus described above and aims to provide a tape speed determining circuit of a relatively simple structure for video signal reproducing apparatus, in which the most appropriate tape speed for reproduction can be automatically selected to provide a reproduced signal with little noise in any case of normal and special forms of reproduction.
As is different from the previously described copending U.
S.
patent application filed by the inventor of the present application on Feb.
1, 1985, in which a specified reference signal is selected from the successively provided reference signals according to the timing with which a reproducing head scans the central portion of a recorded track, the present invention delays by an infinitesimal time "t" i.
e.
a very short period of time, substantially shorter than a field period, the timing for selection of specified reference signals from a plurality of kinds, for example, four kinds of reference signals cyclically supplied.
During the delayed time, an error signal is generated by a pilot signal reproduced in this time and a reference signal supplied since these signals have difference frequencies.
Then, the error signal is sampled, and based on a cycle of a fundamental wave component of the sampling output, the recording mode of a signal recorded in the video tape is determined.
It has been determined that if a reference signal having a different frequency from that of a reference signal for tracking is supplied in a time "t" sufficiently shorter than a field period after the start of the scanning of a recorded track by a reproducing head or sufficiently shorter than a field period immediately before the end of the scanning, such supply of a reference signal of different frequency does not affect tracking control of the whole recorded track since the time "t" is a very short period close to the start or the end of the scanning of the recorded track
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