Azimuth recording

Last updated

Azimuth recording is the use of a variation in angle between two recording heads that are recording data so close together on magnetic tape 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.

Contents

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 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. [1] [2] [3]

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

See also

Related Research Articles

<span class="mw-page-title-main">Magnetic tape</span> Medium used to store data in the form of magnetic fields

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 tape could with relative ease record and playback audio, visual, and binary computer data.

<span class="mw-page-title-main">VHS</span> Consumer-level analog videotape recording and cassette form standard

The VHS is a standard for consumer-level analog video recording on tape cassettes, invented in 1976 by the Victor Company of Japan (JVC). It was the dominant home video format throughout the tape media period in the late 1970s, 1980s, 1990s, and early 2000s.

<span class="mw-page-title-main">Videotape</span> Magnetic tape used for storing video and sound simultaneously

Videotape is magnetic tape used for storing video and usually sound in addition. Information stored can be in the form of either an analog or digital signal. Videotape is used in both video tape recorders (VTRs) and, more commonly, videocassette recorders (VCRs) and camcorders. Videotapes have also been used for storing scientific or medical data, such as the data produced by an electrocardiogram.

<span class="mw-page-title-main">S-VHS</span> Improved version of VHS

S-VHS (スーパー・ヴィエイチエス), the common initialism for Super VHS, is an improved version of the VHS standard for consumer-level video recording. Victor Company of Japan introduced S-VHS in Japan in April 1987, with their JVC-branded HR-S7000 VCR, and in certain overseas markets soon afterward. By the end of 1987, the first S-VHS VCR models from other competitors included Hitachi VT-2700A, Mitsubishi HS-423UR, Panasonic PV-S4764, RCA VPT-695HF, and Toshiba SV-950. It has been standardized as IEC 60774-3 and IEC 60774-4.

<span class="mw-page-title-main">Betamax</span> Consumer-level analog video tape recording and cassette form factor standard

Betamax 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, followed by the US in November of the same year.

<span class="mw-page-title-main">Helical scan</span> Method of recording high-frequency signals on magnetic tape

Helical scan is a method of recording high-frequency signals on magnetic tape, used in open-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives.

Betacam is a family of half-inch professional videocassette products developed by Sony in 1982. In colloquial use, Betacam singly is often used to refer to a Betacam camcorder, a Betacam tape, a Betacam video recorder or the format itself.

<span class="mw-page-title-main">Video tape recorder</span> Tape recorder designed to record and play back video and audio material on magnetic tape

A video tape recorder (VTR) is a tape recorder designed to record and playback video and audio material from magnetic tape. The early VTRs were open-reel devices that record on individual reels of 2-inch-wide (5.08 cm) tape. They were used in television studios, serving as a replacement for motion picture film stock and making recording for television applications cheaper and quicker. Beginning in 1963, videotape machines made instant replay during televised sporting events possible. Improved formats, in which the tape was contained inside a videocassette, were introduced around 1969; the machines which play them are called videocassette recorders.

<span class="mw-page-title-main">Video Cassette Recording</span> Magnetic tape-based videocassette format

Video Cassette Recording (VCR) is an early domestic analog recording format designed by Philips. It was the first successful consumer-level home videocassette recorder (VCR) system. Later variants included the VCR-LP and Super Video (SVR) formats.

<span class="mw-page-title-main">Tape head</span> Component used to read magnetic tape

A tape head is a type of transducer used in tape recorders to convert electrical signals to magnetic fluctuations and vice versa. They can also be used to read credit/debit/gift cards because the strip of magnetic tape on the back of a credit card stores data the same way that other magnetic tapes do. Cassettes, reel-to-reel tapes, 8-tracks, VHS tapes, and even floppy disks and early hard drive disks all use the same principle of physics to store and read back information. The medium is magnetized in a pattern. It then moves at a constant speed over an electromagnet. Since the moving tape is carrying a changing magnetic field with it, it induces a varying voltage across the head. That voltage can then be amplified and connected to speakers in the case of audio, or measured and sorted into ones and zeroes in the case of digital data.

<span class="mw-page-title-main">8 mm video format</span> Magnetic tape-based videocassette format for camcorders

The 8mm video format refers informally to three related videocassette formats. These are the original Video8 format and its improved successor Hi8, as well as a more recent digital recording format known as Digital8. Their user base consisted mainly of amateur camcorder users, although they also saw important use in the professional television production field.

<span class="mw-page-title-main">U-matic</span> Videocassette format; the first of its kind

U-matic or 34-inch Type E Helical Scan or SMPTE E 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 opposed to the various reel-to-reel or open-reel formats of the time. The videotape is 34 in (19 mm) wide, so the format is often known as "three-quarter-inch" or simply "three-quarter", compared to open reel videotape formats in use, such as 1 in (25 mm) type C videotape and 2 in (51 mm) quadruplex videotape.

<span class="mw-page-title-main">Type C videotape</span> Broadcast magnetic tape-based videotape format

1-inch Type C Helical Scan or SMPTE C is a professional reel-to-reel analog recording helical scan videotape format co-developed and introduced by Ampex and Sony in 1976. It became the replacement in the professional video and broadcast television industries for the then-incumbent 2–inch quadruplex videotape open-reel format. Additionally, it replaced the unsuccessful type A format, also developed by Ampex, and primarily in mainland Europe, it supplemented the type B format, developed by the Fernseh division of Bosch.

<span class="mw-page-title-main">HDCAM</span> Magnetic tape-based videocassette format for HD video

HDCAM is a high-definition video digital recording videocassette version of Digital Betacam introduced in 1997 that uses an 8-bit discrete cosine transform (DCT) compressed 3:1:1 recording, in 1080i-compatible down-sampled resolution of 1440×1080, and adding 24p and 23.976 progressive segmented frame (PsF) modes to later models. The HDCAM codec uses rectangular pixels and as such the recorded 1440×1080 content is upsampled to 1920×1080 on playback. The recorded video bit rate is 144 Mbit/s. Audio is also similar, with four channels of AES3 20-bit, 48 kHz digital audio. Like Betacam, HDCAM tapes were produced in small and large cassette sizes; the small cassette uses the same form factor as the original Betamax. The main competitor to HDCAM was the DVCPRO HD format offered by Panasonic, which uses a similar compression scheme and bit rates ranging from 40 Mbit/s to 100 Mbit/s depending on frame rate.

<span class="mw-page-title-main">Type B videotape</span> Broadcast magnetic tape-based videotape format used in Europe

1-inch Type B Helical Scan or SMPTE B is a reel-to-reel analog recording video tape format developed by the Bosch Fernseh division of Bosch in Germany in 1976. The magnetic tape format became the broadcasting standard in continental Europe, but adoption was limited in the United States and United Kingdom, where the Type C videotape format met with greater success.

V-Cord is an analog recording videocassette format developed and released by Sanyo. V-Cord was released in 1974, and could record 60 minutes on a cassette. V-Cord II, released in 1976, could record 120 minutes on a V-Cord II cassette.

<span class="mw-page-title-main">EIAJ-1</span> Standard for video tape recorders

EIAJ-1 was a standard for video tape recorders (VTRs) developed by the Electronic Industries Association of Japan with the cooperation and assistance of several Japanese electronics manufacturers in 1969. It was the first standardized format for industrial/non-broadcast VTRs using a helical scan system employing open reel tape. Previously, each manufacturer of machines in this market used a different proprietary format, with differing tape speeds, scanner drum diameters, bias frequencies, tracking head placement, and so on, although most used 1/2" wide tape. As a result, video tapes recorded on one make and/or model of VTR could only be interchanged with other machines using that specific format, hampering compatibility. For example, a reel of tape recorded on a Panasonic machine would not play on a Sony machine, and vice versa. The EIAJ-1 standard ended this incompatibility, giving those manufacturers a standardized format, interchangeable with almost all VTRs subsequently brought to market around that time. The format offered black-and-white video recording and playback on 1/2″ magnetic tape on a 7″ diameter open reel, with portable units using smaller 5″ diameter reels.

VK is a helical scan analog recording videocassette format developed by Akai in the late 1970s, that is capable of recording and playing back black & white video in either EIA and CCIR systems.

<span class="mw-page-title-main">Videocassette recorder</span> Device which records and plays back audio-visual media

A videocassette recorder (VCR) or video recorder is an electromechanical device that records analog audio and analog video from broadcast television or other AV sources and can play back the recording after rewinding. The use of a VCR to record a television program to play back at a more convenient time is commonly referred to as time shifting. VCRs can also play back prerecorded tapes, which were widely available for purchase and rental starting in the 80s and 90s, most popularly in the VHS videocassette format. Blank tapes were sold to make recordings.

From 1963 to 1970, Ampex manufactured several models of VTR 2-inch helical VTRs, capable of recording and playing back analog black and white video. Recording employed non-segmented helical scanning, with one wrap of the tape around the video head drum being a little more than 180 degrees, using two video heads. One video drum rotation time was two fields of video. The units had two audio tracks recorded on the top edge of the tape, with a control track recorded on the tape's bottom edge. The 2-inch-wide video tape used was one mil thick. The VTRs were mostly used by industrial companies, educational institutions, and a few for in-flight entertainment.

References

  1. Tozer, E. P. J. (November 12, 2012). Broadcast Engineer's Reference Book. CRC Press. ISBN   9781136024184 via Google Books.
  2. Capelo, Gregory; Brenner, Robert C. (June 26, 1998). VCR Troubleshooting and Repair. Newnes. ISBN   9780750699402 via Google Books.
  3. Trundle, Eugene (May 12, 2014). Newnes Guide to TV and Video Technology. Elsevier. ISBN   9781483183169 via Google Books.