Pilot tone, a precursor of SMPTE time code, is typically encountered when working with open reel audio used in film or video production. The tone is a 50 or 60 Hz signal sent from a motion picture camera and recorded on one track of the tape. Not to be confused with hum, during production this tone was used for synchronizing tape playback to picture by matching the camera speed.1 Crosstalk is reduced by recording the tone 180 degrees out of phase with respect to the program so that it will cancel out during playback.
Numerous sync tone systems have been developed over time. More detail on these can be found in EBU-Tech 3086.
- The Pilot Tone system
- The Perfectone system
- The Neopilot system
- The Ranger system
- The Telefunken system
- The Synchrotone system
- The Leevers-Rich system
- The BBC system
- The Fairchild system
Can it be fixed?
Transferring any tape with sync tone requires an appropriate playback head (most likely a head with center-track timecode). See this Richard Hess blog post on synchronization. If the tape is played back on a two-track head, for instance, the tone will not cancel out.
Listen to a tape with pilot tone on SoundCloud
1. G. D. White, The audio dictionary (3rd ed.), (Seattle: University of Washington Press, 2005), 291. ↩