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Media type | magnetic tape |
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Usage | recording high-frequency signals |
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.
With this technique, magnetic tape heads (or head chips) are placed on a rotating head drum [1] . which run the chips at high speed (or angular velocity). The tape is wrapped tightly around the drum. Either the drum [2] and/or the tape is tilted at an angle that allows the head chips to read the tape diagonally faster, so the linear speed of the tape may be slower than the speed of the head chips, which rotate at a higher speed allowing signals to be transmitted. high frequency, such as video, are recorded. [3] [4] [5] The diagonal tracks read or written using this method are known as helical tracks. [2]
There are several types of helical scan. These include:
Many helical scan cassette formats such as VHS and Betacam use a head drum with heads that use azimuth recording, in which the heads in the head drum have a gap that is tilted at an angle, and opposing heads have their gaps tilted so as to oppose each other. [20] [21] This eliminates the need for guard bands between the helical tracks allowing for a higher density of information on the tape. [22] [23] [24]
Earl Edgar Masterson from RCA patented the first helical scan method in 1950. [25] [26] German engineer Eduard Schüller developed a helical scan method of recording in 1953 while working at AEG. [27] [28] With the advent of television broadcasting in Japan in the early 1950s, they saw the need for magnetic television signal recording. Dr. Kenichi Sawazaki developed a prototype helical scan recorder in 1954. [29] Helical scan machines were demonstrated by Toshiba in 1959 and since they recorded one field of video per track, they were the first to allow video to be paused and played back at speeds other than real time. Helical scan type B and type C videotape began to be used in 1976. [30]
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 1980s and 1990s.
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.
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 a portmanteau, created by its founder, which stands for Alexander M. Poniatoff Excellence. Ampex operates as Ampex Data Systems Corporation, a subsidiary of Delta Information Systems, and consists of two business units. The Silicon Valley unit, known internally as Ampex Data Systems (ADS), manufactures digital data storage systems capable of functioning in harsh environments. The Colorado Springs, Colorado, unit, referred to as Ampex Intelligent Systems (AIS), serves as a laboratory and hub for the company's line of industrial control systems, cyber security products and services and its artificial intelligence/machine learning technology.
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.
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.
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.
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.
A recording head is the physical interface between a recording apparatus and a moving recording medium. Recording heads are generally classified according to the physical principle that allows them to impress their data upon their medium. A recording head is often mechanically paired with a playback head, which, though proximal to, is often discrete from the record head.
U-matic or 3⁄4-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 3⁄4 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.
1–inch Type 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 invented by Ampex, and, primarily in mainland Europe, it supplemented the type B format, invented by the Fernseh division of Bosch, but it was replaced by type C format also there.
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.
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 uncompressed digital video on a tape cassette; however, it stores a composite video signal, rather than component video as with D-1. While component video is superior for advanced editing, especially when chroma key effects are used, composite video was more compatible with most analog facilities existing at the time.
2-inch quadruplex videotape was the first practical and commercially successful analog recording video tape format. It was developed and released for the broadcast television industry in 1956 by Ampex, an American company based in Redwood City, California. The first videotape recorder using this format was built the same year. This format revolutionized broadcast television operations and television production, since the only recording medium available to the TV industry until then was Motion picture film.
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, 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.
D-9 or Digital-S as it was originally known, is a professional digital video videocassette format created by JVC in 1995.
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.
IVC 2 inch Helical scan was a high-end broadcast quality helical scan analog recording VTR format developed by International Video Corporation (IVC), and introduced in 1975. Previously, IVC had made a number of 1 inch Helical VTRs. IVC saw a chance to make a VTR that would have the quality of the then-standard 2 inch Quadruplex videotape format but with the advantages of helical scan. They then developed a VTR using this technology, the IVC Model 9000.
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.
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.
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