Magnetic tape reproducer-recorder with means for tape segment

Abstract

Tape segment identifying signals in a frequency range below the lower threshold of sound signals that can be recorded or played back from the tape are recorded on the sound track of a video tape, a characteristic such as the frequency, pulse length, or phase of the identifying signals being changed stepwise as successive tape segments corresponding to successive scenes or successive periods of playing time are recorded. To find a selected segment for playback, beginning when the tape is in any position in the machine, the tape transport mechanism is put into the fast-forward or reverse mode, the identifying signals are filtered by a low-pass filter having a cutoff frequency dependent upon tape speed and then are passed through a pulse-shaping circuit to produce square waves, after which the frequency, pulse length or phase is digitally measured and compared with a selected value representing the segment to be found, using synchronizing pulses, such as the vertical synchronizing pulses of a television signal, as reference signals. The detection circuit is so coordinated with the direction of tape transport as to produce a 'match' signal at the beginning of the tape segment selected, which signal puts the equipment in readiness for playback.