A system for the synchronization of a motion picture camera with a ” tape recorder recording the sound, using a superimposed crystal sync pilot tone generated by the camera or an oscillator, usually at 50Hz or 60Hz, on the full-track tape in such a way that it is not sensed by the normal full-track playback head, and so is not heard with the recorded sounds. The recovered signal is used to control the speed of the tape recorded in playback so the sound remains in sync with the picture. This process is called resolving. Developed for use in analog, mono Nagra recorders.

The sync head records two thin tracks of sync tone near the center of the tape. These thin tracks are read by the resolving circuits that control the motor speed of the player to maintain correct synchronization. As the sync signals are in antiphase, when both tracks pass the play-back head simultaneously, they are phase-cancelled.

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