Pilottone
From Wikipedia, the free encyclopedia
Pilottone and the related neo-pilottone are special synchronization signals recorded by analog audio recorders designed for use in motion picture production. Before the adoption of timecode by the motion picture industry in the late 1980s, pilottone-sync was the basis of all magnetic motion picture sound recording systems.
The synchronization is obtained when a pulse cable is connected from Motion picture camera to an audio recorder such as those made by Nagra. A camera with a Sync motor sends a 60/50 Hz signal to the recorder. This sine wave is recorded in the centre of the audio tape by a special push-pull head (The recorded pilot frequency can only be played back by push-pull head and not by any normal playback head) All the speed variations of the camera and tape are recorded as on pilot track as deviations from 60/50 Hz, and compared at the time of playback with in built quartz reference oscillator. These variations are rectified at the time of transfer to the perforated 35mm/16mm tape. At that time the mains power supply frequency is also taken as reference. (The selection of the 60/50 Hz equipment depends on the power supply in the country where filming is being conducted. North America has a supply of 60 Hz whereas Europe and some Asian countries have 50 Hz.)
Normal audio recorders have a good system for regulating their speed with a tachometer, but such a system cannot guarantee that a playback machine will exactly match the speed of the recorder over long periods of time. Such a system would need to record exactly how much tape passes the head in such an amount of time, and would have to be accurate to a quarter inch after 800 feet or more. Pilottone provides such a system.
When the tape is played back on a pilottone-reading tape player, it needs to only resolve the pilottone signal on the tape. The player has a quartz oscillator of its own, and when the operator hits play, the player tries to match the sine wave of the recorded pilottone with the pilottone being generated by its own quartz crystal. When they match up, the player knows that the tape is moving across its play head exactly as fast as it was across the record head when it was originally recorded.
The pilot tone system is now obsolete. The use of SMPTE timecode in digital format ensures a rock steady speed for all recorders and cameras. All new digital recorders and VCRs use this system. This reference Timecode is generated with the help of a built-in quartz oscillator.
In such a situation when the speeds of the camera and the recorder are absolutely free of any variations there remains no need for a pulse cable to run between the camera and the recorder. This has made the work of a sound man much simpler. It also give more freedom of movement to the camera at the time of motion picture filming.
