2 inch Quadruplex videotape

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2 inch Quadruplex (also called 2″ Quad, or just quad, for short) was the first practical and commercially successful videotape format. It was developed and released for the broadcast television industry in 1956 by Ampex, an American company based in Redwood City, California. This format revolutionized television broadcast operations and production, since the only medium available to the TV industry before then was motion picture film used for kinescopes, which was much more costly to utilize, had lower image quality than videotape, and took time to develop as well.

Since most West Coast network delays done by the TV networks at the time were done with film kinescopes that needed time for developing, the networks wanted a more practical, cost-effective, and quicker way to time-shift programming for later airing in the West Coast (as well as a general production medium that was not as costly or time-consuming to edit and develop as film). These reasons were part of the motivation for designing a video recording technology that used magnetic tape, in this case, the 2 inch Quad.

The format gets its official name of Quadruplex from the fact that it uses 4 heads mounted on a headwheel spinning tranversely (width-wise) across the tape at a rate of 14,400 rpm for NTSC-standard Quad decks, and 15,000 rpm for those using the European PAL video standard. This method was called quadrature scanning (as opposed to the helical scan transport used by later videotape formats). The tape ran at a speed of either 7.5 or 15 inches per second (190 or 380 mm/s), 15.625 inches per second (400 mm/s) PAL, and the audio, control, and cue tracks were recorded in a standard linear fashion on the edges of the tape. The cue track was used either as a second audio track, or for recording cue tones or time code for editing.

A typical 4800 foot (1500 m) reel of 2 inch quad tape holds approximately 1 hour of recorded material at 15 inches per second (380 mm/s).

A reel of 2 inch quad videotape compared with a modern-day miniDV videocassette

Each transversely-recorded track of video on a 2 inch Quad videotape holds one-sixteenth of a field of video. In other words, the format used segmented recording. This meant that 2 inch Quad was not capable of "trick-play" functions, such as still, shuttle, and reverse/variable-speed playback. But the format had quite sufficient image quality for broadcast (it produced about 400 lines of video resolution), and remained the de-facto format and industry standard for television broadcasting from its inception in 1956 to the mid-1980s, when newer, smaller, and lower-maintenance videotape formats supplanted the role of 2 inch quad.

There were 3 different variations of 2 inch Quad:

Low-band, which was the first variety of Quad introduced by Ampex in 1956,
High-band, which used a wider bandwidth for recording video to the tape, resulting in higher-resolution video from the VTR, and
Super High-band, which used a pilot tone for better timebase stability, and higher coercivity tape.

Most Quad machines made later in the 60s and 70s by Ampex could playback both low and high-band 2 inch Quad tape.

1 The beginning of Quad
2 2 inch Quad today
3 See also
4 External links

[edit] The beginning of Quad

At the beginning of the 1950's, several companies along with Ampex, such as Bing Crosby Enterprises (BCE), and RCA were all competing to release a videotape format. RCA and BCE did release working prototypes of their recorders, but their downfall was that they all used a longitudinal (stationary-head) method of recording, much like audio tape recorders. This meant that the tape had to be recorded at a ludicrously high speed (around 120 in/s) in order to record a sufficient amount of bandwidth to reproduce an adequate video image (at least 2-3 MHz for a watchable image), in turn requiring large amounts of tape on large reels used by these early machines from RCA and BCE. In Britain at that time, the BBC developed a similar stationary-head VTR system that saw some on-air use, called VERA (Vision Electronic Recording Apparatus).

Plus, time-shifting of television programming for the West Coast by the networks at the time (in order to broadcast their programming at the same local time in the East and West Coasts) using film kinescopes was quite a rushed and perilous ordeal. This was due to there being only 3 hours for the West Coast branches of the TV networks to receive video for the programming from the East Coast (live via leased microwave relay or coaxial cable circuits provided from the phone company (AT&T) at the time), and then to record such to film kinescopes, and lastly to develop the film to be aired 3 hours later on the West Coast. This usually meant the kinescope film was aired almost immediately after it came straight out of the developing equipment, still warm from the film dryer used to dry the film prints coming out of the developing chemicals. These were referred to by the networks as "hot kines". According to the History of Tape Recording website, the networks used more raw film stock for kinescope delays for the West Coast than all of the Hollywood film studios combined. They were desperate to obtain a quicker, less expensive, and more practical solution.

Ampex, seeing the impracticality of the prototype BCE and RCA VTRs, started to develop a more practical videotape format with tape economy in mind, as well as providing a solution to the networks' West Coast delay woes. Starting in 1952, Ampex built the Mark I prototype VTR, using 2 inch wide tape. Ampex decided that instead of having the tape move fast across the head to record enough bandwidth for video, that the head move fast across the tape instead. This resulted in the Mark I using arcuate scanning, which consisted of a spinning disk, where its face (where the heads were mounted) was in contact with the tape (as opposed to the edge of the headwheel with transverse quadrature scanning). This resulted in an arc-shaped track being recorded across the width of the tape. Arcuate scanning resulted in a head-to-tape speed of about 2500 in/s, but problems with timebase stability of the reproduced video signal from the tape led Ampex to abandon arcuate scanning in favor of the more reliable transverse scanning system.

Ampex soldiered on throughout the mid-50s with the Mark II and Mark III prototype recorders, which now used transverse scanning. The Mark II used frequency modulation for recording video to tape, resulting in a much-improved, but still noisy video image (the Mark I had used amplitude modulation), and the Mark III had improved signal-processing and servo electronics, resulting in perfect video being reproduced from the machine.

The Mark III worked perfectly, but its appearance was quite that of a prototype, and not a finished, saleable product. It was in a makeshift wooden case, with several parts of its chassis externally mounted in partially-filled racks. So, Ampex went on to integrate all of this into a sleek metal console and fully-populated rack-mount cases, and this became the Mark IV.

The Mark IV was the machine for the first public demonstration of the 2 inch Quad format, at the NARTB (now the NAB) convention in Chicago on April 14, 1956. The earlier Mark III was given some cosmetic improvements, and was also demonstrated at Ampex headquarters in Redwood City the same day. Both demonstrations were a success, and as a result, Ampex was swamped with orders for the new 2 inch Quad VTR.

The VR 1000-B model (1961)

Ampex later released the first manufactured models of Quad VTR based on the Mark IV which were also prototypes, the VRX-1000, of which 16 were made. Machines made afterward were the final production models, and were designated as the VR-1000.

Shortly after Ampex's introduction of the 2 inch quad format, RCA in 1957 introduced a Quad-compatible VTR, the TRT-1A. RCA referred to it as a "Television Tape Recorder", since the word "Videotape" was a trademark of Ampex at the time.

Later on, Ampex would release later models of their Quad decks, such as the second-generation VR-2000 in 1967, and the AVR series of VTRs, AVR-1, AVR-2, and AVR-3 in the 1970s. The AVR-2 was the most compact of Quad VTRs, and could run off on regular 120 volt single-phase household-type AC power (Quad VTRs before then required 208 or 220-volt 3-phase AC power).

RCA would also release later models of Quad VTRs as well, such as the TR-22 and TR-600.

CBS was the first television network to use 2 inch Quad videotape, using it for a West Coast delay of Douglas Edwards and the News on November 30, 1956. CBS would also delay for the west coast the first entertainment tv program on videotape, The Edsel Show, on October 13, 1957.

The developing engineers at Ampex that worked on 2 inch Quadruplex videotape from the Mark I to the VR-1000 were Charles Ginsburg, Alex Maxey, Fred Pfost, Shelby Henderson, Charlie Anderson, and Ray Dolby (who later went on to found Dolby Laboratories).

[edit] 2 inch Quad today

Nowadays, 2 inch Quad is no longer used as a mainstream format in TV broadcasting and video production, having been supplanted by more modern, easier-to-use, more practical and lower-maintenance formats like 1" Type C (1976), U-matic, Betacam, DVCAM, DVCPro, and HDCAM.

When it was in use, 2 inch Quad VTRs needed ongoing maintenance, usually 3-phase power to operate (as mentioned earlier), plus an air compressor to provide air pressure for the air bearing that the spinning transverse headwheel rode on due to its high rotational speed (some Quad VTRs, such as the portable Ampex VR-3000, used ball bearings instead due to the lack of availability of compressed air, but these wore out quickly). They also required constant calibration of the discrete electronics used by the older Quad VTRs in order to maintain a high-quality picture suitable for broadcast. The operator was a much more skilled technician than today's "pop-in-a-cassette" operators. These machines required quite a bit of set up in order to make a quality recording and a broadcast quality image for playback.

2 inch Quad VTRs today are not used for broadcast or production service. The few that remain in service are now used by video archives and transfer services, for the transfer and/or restoration of 2 inch quad videotape material to a newer format.

[edit] See also

Videotape
Contrast with Helical scan recording

[edit] External links

v • d • e Industrial & home video media
Magnetic tape	VERA (1952) - 2 inch Quadruplex videotape (1956) - 1 inch type A videotape (1965) - U-matic (1969) - Video Cassette Recording (1972) - V-Cord (1974) - VX (aka "The Great Time Machine") (1974) - Betamax (1975) - 1 inch type B videotape (1976) - 1 inch type C videotape (1976) - VHS (1976) - Video 2000 (1979) - VHS-C (1982) - M (1982) - Betacam (1982) - Video8 (1985) - MII (1986) - D1 (1986) - S-VHS (1987) - D2 (1988) - Hi8 (1989) - D3 (1991) - D5 (1994) - Digital-S (D9) (199?) - S-VHS-C (1987) - W-VHS (1992) - DV (1995) - Betamax HDCAM (1997) - D-VHS (1998) - Digital8 (1999) - HDV (2003)
Optical discs	Laserdisc (1978) - Laserfilm (1984) - CD Video - VCD (1993) - DVD (1996) - MiniDVD - CVD (1998) - SVCD (1998) - FMD (2000) - EVD (2003) - FVD (2005) - UMD (2005) - VMD (2006) - HD DVD (2006) - Blu-ray Disc (BD) (2006) - DMD (2006?) - AVCHD (2006) - Tapestry Media (2007) - HVD (TBA) - Protein-coated disc (TBA) - Two-Photon 3-D (TBA)
Grooved Videodiscs	SelectaVision (1981) - VHD (1983)