(1) (noun) The electronic circuit within or connected to a Nagra or other synchronous tape recorder that acts as a servo to control motor speed on playback to maintain proper synchronization of sound with picture. It keeps the recorded sync tone in phase with the 60Hz AC powering the recorder and projector, or can sync the playback with crystal sync, or other reference source.
(2) (verb) The process of regulating audio and/or video tape speed by comparing a reference tone on the tape with an external master and adjusting the speed of the first device so that the two stay in sync is called resolving. This can be done striping the tapes with a pilot tone, or by a time code such as SMPTE. The master deck reads the location from all slave machines and fast-forwards or reverses them until it reads the same time code from every machine. It then monitors the time code adjusts the slaves’ transports continually to maintain frame lock. See also resolver, reference source.