Sel-Sync or Selective Synchronous recording is the process of selectively using audio tape record heads as play back heads so that new signals can be recorded on other tracks in perfect sync with the existing tracks. Sel-sync recording dramatically changed the recording process allowing

overdubbing Overdubbing (also known as layering) is a technique used in audio recording in which audio Music track, tracks that have been pre-recorded are then played back and monitored, while simultaneously recording new, doubled, or augmented tracks onto o ...

of individual recorded tracks. Sel-sync along with the multi-track head was invented by Ross S. Snyder at

Ampex Ampex Data Systems Corporation is an American electronics company founded in 1944 by Alexander M. Poniatoff as a spin-off of Dalmo-Victor. The name ''AMPEX'' is an acronym, created by its founder, which stands for Alexander M. Poniatoff Excell ...

in 1955. Three problems had to be solved: mechanical alignment, switching of the record track to playback mode and multitrack erase head. The hard problem was the switching of a track between record and playback mode, as the impedance of record heads are quite different from the impedance of play back heads. Prior to Sel-Sync record heads were directly wired to the record electronics and playback heads were directly wired to the playback electronics. Also the designs of the two heads were very different. The problem of switching very low-level/high-impedance circuitry without introducing hum or

noise Noise is sound, chiefly unwanted, unintentional, or harmful sound considered unpleasant, loud, or disruptive to mental or hearing faculties. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrat ...

had to be solved. Mort Fujii in the Ampex special projects lab was responsible for the actual design. Ampex did not patent Sel-Sync because Ross Snyder did not think it would be of interest to more than a few musicians and an Ampex lawyer said the idea was "obvious", hence unpatentable. Ampex only trademarked the name. Sel-Sync remained an external, add-on function until the AG-440 and later series, wherein Sel-Sync was integrated into every electronics, although for obvious reasons Sel-Sync is useful only with multi-track machines (more than one track, and, usually, three or more tracks).

D-2 (video) D-2 is a professional digital videocassette format created by Ampex and introduced in 1988 at the NAB Show as a composite video alternative to the component video D-1 format. It garnered Ampex a technical Emmy in 1989. Like D-1, D-2 stores ...

was the first

digital recording In digital recording, an audio signal, audio or video signal is converted into a stream of discrete numbers representing the changes over time in air pressure for audio, or Color, chroma and luminance values for video. This number stream is s ...

video tape format to offer Sel-Sync "read before write" (an Ampex term) also known as "preread" on

Sony is a Japanese multinational conglomerate (company), conglomerate headquartered at Sony City in Minato, Tokyo, Japan. The Sony Group encompasses various businesses, including Sony Corporation (electronics), Sony Semiconductor Solutions (i ...

magnetic tape Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic ...

recorders. Read before write allowed simultaneous playback and recording on the same VCR.

References

{{Reflist Sound recording technology 1955 introductions