Tape speed determining apparatus for video signal reproducing apparatus

Claim 1

A tape speed determining apparatus for a video signal recording/reproducing apparatus, operable at a plurality of operating speeds, using a helical scanning system in which a video signal including a plurality of fields recorded on a video tape in a slanted manner is reproduced by means of a rotating head system in which a plurality of reproducing heads which are switched by a reproducing head selection pulse are mounted on a rotating body, said video tape being recorded with a signal that is intended to be reproduced at one of said plurality of operating speeds, said recording/reproducing apparatus using a pilot signal system wherein a plurality of pilot signals recorded with said video signal in an overlapping manner are reproduced and wherein reference signals are supplied with predetermined timing, said tape speed determining apparatus comprising: timing pulse generator means for deriving timing pulses in response to said reproducing head selection pulse, including means for generating timing pulses that last for an infinitesimal period of time, and delay means for delaying by said period of time selection of reference signals from among said reference signals; error signal detecting means for detecting, during said infinitesimal period of time, an error signal generated by comparison of the levels of two beat frequencies of said pilot signals, said error signal being sampled by said timing pulses and converted to a pulsed waveform representative of amplitudes of a sequence of said error signals the polarity of which is inverted for alternate fields; low pass filter means for deriving from said pulsed waveform a fundamental wave; and means for determining from the frequency and waveform of said fundamental wave whether an operating speed at which said fundamental wave is produced is the intended reproduction speed of said video signal and for providing a signal indicative of said determination.