Videotape Recorders

A video signal consists of changes of information which occur at rates between 50 times and 5.5 million times a second! If the magnetic tape is not moving sufficiently fast there will be insufficient room to record details of the video signal. Fast tape motion poses problems, and uses a lot of tape. So instead, the record/replay head itself is made to pass rapidly over a slow-moving tape, effectively producing a high recording speed. The result is a series of parallel slanting tracks across the tape.

Cassette VTRs

Open-reel videotape recorders (VTRs) have been superseded by a variety of cassette-based formats most of which are incompatible with one another. The professional formats are as follows:

● U-matic High Band, a now largely obsolete system using 3/4-inch wide tape.

● Betacam SP, a high quality analogue system using 1/2-inch wide metal tape.

● Mil, a high-quality analogue system using 1/2-inch wide metal tape, but contained in a different sized cassette from Betacam SP.

● D1, a digital component system using 3/4-inch tape. This format is being superseded by other digital formats

● D2, a digital composite system using 3/4-inch tape. Obsolescent.

● D3 or DX, a composite digital system using 1/2-inch wide tape.

● D5, a component linear digital system using 1/2-inch wide tape.

● Digital Betacam, a component data compressed system using 1/2-inch wide tape. Digital Betacam machines can replay tapes recorded with an analogue Betacam SP machine.

By recording a signal in a digital form, very robust ‘transparent’ recordings are made, i.e. the replayed signal is identical to the original signal. When choosing which type of VTR to purchase, consideration should be given to budgets and applications, but beware: cheaper machines do not produce robust recordings. Picture quality degrades markedly from one ‘generation’ of recording to the next. If much editing/post-production is likely, then it is better to invest in higher-quality machines.

Typical idealised helical scan VTR format

Tape formats