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 magnet ...

that

crosstalk In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, i ...

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 In physics, interference is a phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude. Constructive and destructive ...

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 A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filte ...

effect on

noise Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference aris ...

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 U-matic is an analogue recording videocassette format first shown by Sony in prototype in October 1969, and introduced to the market in September 1971. It was among the first video formats to contain the videotape inside a cassette, as opp ...

, used this system. Later, the JVC VHS and the Sony

Betamax Betamax (also known as Beta, as in its logo) is a consumer-level analog recording and cassette format of magnetic tape for video, commonly known as a video cassette recorder. It was developed by Sony and was released in Japan on May 10, 1975, ...

used slant azimuth recording also. These digital VTR versions used azimuth recording as well.

References

mrbetamax.com
Mr. betamax, Helical Azimuth Recording
Canon
Video Recording System Two rotating heact, 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 Engineers
The Videotape Recorder: Its Evolution and the Present State of the Art of VTR Technology, by Hiroshi Sugaya1, September 17, 1985. Computer storage tape media {{Electronics-stub

See also

References