Azimuth recording is the use of a variation in angle between two recording heads that are recording data so close together on
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 ...
that
crosstalk would otherwise likely occur. Normally, the head is perpendicular to the movement of the tape, and this is considered zero degrees. However, if the heads are mounted at slightly different angles (such as ±7 degrees in
VHS),
destructive interference will occur at high frequencies when reading data recorded in the cross-talking channel but not in the channel that is intended to be read. At low frequencies relative to the maximum allowed by the head gap, however, this technique is ineffective. Thus one head is slanted slightly leftwards and the magnetic gap of the other head slanted slightly rightwards.
To look at it another way, channel A sees the channel B data stretched out in time, hence the technique has a
low-pass effect on
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 ...
intruding from another channel.
Every videotape system was designed to put as much video as possible onto a given-sized tape, but information from one recording track (pass of the video head) must not interfere with information on adjacent stripes. Using slant azimuth recording, the need for guard bands, that is the blank space between tracks, is eliminated, allowing more recording to be placed on a given length of tape.
All the early low-end reel-to-reel VTR machines and the first
VCR cassette formats, the Philips and the Sony
U-matic, used this system. Later, the JVC
VHS and the Sony
Betamax
Betamax (also known as Beta, and stylized as the Greek letter Beta, β in its logo) is a discontinued consumer analog Videotape, video cassette recording format developed by Sony. It was one of the main competitors in the videotape format war ag ...
used slant azimuth recording also. Digital VTR formats used azimuth recording as well.
See also
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Symmetric Phase Recording
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VTR
*
Tape head
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Helical scan
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Slant azimuth recording
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Betamax
Betamax (also known as Beta, and stylized as the Greek letter Beta, β in its logo) is a discontinued consumer analog Videotape, video cassette recording format developed by Sony. It was one of the main competitors in the videotape format war ag ...
References
External links
CanonVideo Recording System Two rotating head, helical scan azimuth recording.
The Art of Digital Video By John Watkinson, page 570
Video engineering By Arch C. Luther, Andrew F. Inglis, page 302.
Google Patents Magnetic head for azimuth recording in a high density magnetic recording system, Ken Takahashi ''et al.''
Society of Motion Picture and Television EngineersThe Videotape Recorder: Its Evolution and the Present State of the Art of VTR Technology, by Hiroshi Sugaya1, September 17, 1985.
Computer storage tape media
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