Quadruplex videotape

Quadruplex videotape

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 and took more time to develop.

Since most United States 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, 2 inch Quad.

The format gets its official name of Quadruplex from the fact that it uses 4 heads mounted on a headwheel spinning transversely (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 (190.5 or 381 mm/s), 15.625 inches per second (396.875 mm/s) PAL, and the audio, control, and cue tracks were recorded in a standard linear fashion near 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 (381 mm/s).

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 1960s and 1970s by Ampex could play back both low and high-band 2 inch Quad tape.

The beginning of Quad

Time-shifting of television programming for the West Coast of the United States by the networks in the 1950s (in order to broadcast their programming at the same local time in the East and West Coasts) using kinescopes films was quite a rushed and perilous ordeal. This was due to there being only three 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 by the phone company (AT&T) at the time), and then to record such to kinescope films, and lastly to develop the film to be aired three 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 [http://web.archive.org/web/20040603152849/http://www.tvhandbook.com/History/History_recording.htm 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.

At the beginning of the 1950s, 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 an extremely 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).

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 would 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-1950s 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 National Association of Radio and Television Broadcasters (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.

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. [http://www.meldrum.co.uk/mhp/knackers/behind.html] - TRT Ext. Link]

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.

The Fernseh Div. of Bosch in Germany also released a a model Quad VTR in the 1970s, the BCM-40. It was only marketed in Bosch's home continent of Europe, and was not sold in the US.

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. The CBS show "Arthur Godfrey's Talent Scouts" on December 24 1956 became the first entertainment program to be broadcast live to the nation from New York and taped for a time-delayed rebroadcast in the Pacific Time Zone. [Val Adams, "C.B.S. Shows Off Tape-Recorded TV", "New York Times", Dec 21, 1956, p. 43.] On January 22 1957, the NBC game show "Truth or Consequences", produced in Hollywood, became the first program to be broadcast in all time zones from a prerecorded videotape. ["Daily N.B.C. Show Will Be on Tape", "New York Times", Jan. 18, 1957, p. 31.] "The Edsel Show", on October 13, 1957 was the first CBS entertainment program to be broadcast live to the nation from Hollywood, then "tape-delayed" for rebroadcast in the Pacific Time Zone.

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).

Military applications

Because the VR-3000 model was self-contained portable (see picture below), the US Military used it in a wide variety of reconnaissance applications in various vehicles and aircraft. Its ability to accurately record high frequency signals was a definite advantage for SIGINT applications.

Edit control

*At first Quad editing was done by physically editing (cutting and splicing) the 2" tape. The tape was "developed" using fine iron powder suspended in a liquid solvent. The editor could then see the video tracks and thus know where to cut the tape. Splicing tape was put on the back of the tape to put the scenes together. See linear video editing for details.
*The Ampex breakthrough was Ampex's Editec (1963); by putting cue tones on the tape the editor could make frame-accurate edits.
* RCA had an "Electronic Splicer" in the TR-4/5 and TR-22 for frame-accurate edits.
*EECO created the EECO-900 editor (1967) which used their "On-Time" time code.
*In 1971 CMX introduced the first edit controller using time code for editing. The CMX 200 could control a source and record Quad. CMX continued to make more powerful editors and ones that could control more VTRs.
* In the 1976 the "Mach One" editor came on the market and Quad post-production houses had a choice between Mach One and CMX editors.
*As 1" Type B (1974) and 1" Type C (1976) VTRs came on the market, CMX and Mach One-equipped editing bays sometimes used a combination of both 1" and 2" VTRs.

Product models

**VR-1000 (1956) (VRX-1000) FM Low band, 3 racks of tubes, monochrome. No TBC-Timebase correction
**VR-1000 'Alan' update kit to color solid state, FM high band updateable.
**VR1001 VR-1000 with the transport vertical.
**VR1100E (1966) Ampex Solid State "of VR-1000", defective circuitry designed by Sony.
**VR1195 (1966) VR1100 with many Ampex updates.
**VR-1200 (1966) Solid state, color high band. Analog TBC. Optional Editec.
**VR-1500 (1963) Portable 2-inch unit, 130 lbs and costing under $12,000, 5 ips, first demonstrated 1963 in New York City.
**VR-2000 (1967) Solid state, color high band. Optional Editec, Dropout compensation. Mark 10 head. Analog TBC.
**VR-3000 (1967) Portable VTR with a Mark 11 ball-bearing head. No TBC
**AVR-1 (1973) Very fast VTR, vacuum columns, vacuum capstan, air transport. NTSC/PAL switchable. Analog TBC.
**ACR-25 (1974) Cart VTR, with two AVR-1 type decks.
**ACR-25B (1975) Cart VTR, ACR-25 with AVR-2 digital TBC.
**AVR-2 (1974) Digital TBC, compact Quad used in studios and remote trucks.
**AVR-3 (1975) Last Ampex Quad, digital TBC. Vacuum capstan. Super high band.

*VR-2000, VR-1200 and some updated VR-100, VR-1100E, VR1195 used modules to correct the playback of the videotape. The list of modules are:
**Amtec: Horizontal TBC. All that was needed for B&W playback.
**Colortec: Color TBC in line after the Amtec for color playback.
**Velcomp: Color velocity TBC correction for better color playback. Optional on some models.
**Procamp: Processing amplifier on the final output. New Composite sync insertion, level adjustment.
** Dropout compensation: Replaced snowy video spots where the FM signal on the tape is missing momentary, caused by a defect in the tape. (optional on some models) Ampex and 3M made different models for the VTR.
**Editec: (1963) Cue tone editor for frame accurate editing.
*** The components of the VTR were the Servo System, Video Record (Modulator) and Playback De-modulator) and Power Supply.

**TRT-1A (1957) Tube VTR, 4 racks of tubes.
**TRT-1B (1959) Tube VTR, 3 racks. an available option for color expanded this machine to six racks, which included the color processing equipment and color monitor.
**TR-2 (1960) Tube VTR with some solid state. Low band or monochrome.
**TR-11 (1961) Tube VTR with solid state PS-Power supply.
**TR-22 (1961) Monochrome low band, later color version.
**TR-22C (1964) High-band color.
**TR-2 (1964) Record-only solid state.
**TR-3 (1964) Playback-only solid state.
**TR-4 (1964) Both, solid state.
**TR-5 (1964) Console portable solid state.

**TR-70 (1966) Solid state, high/low band with dropout compensation.
**TR-50 (1967) TR-4 high band.
**TR-60 (1969) High-band color or monochrome.
**TCR-100 (1970) Dual-deck video cartridge machine.
**TR-61 (1972) High-band color, digital servo system, NTSC/PAL switchable.
**TPR-10 (1975) High-band color portable.
**TR-600 (1972) Last RCA Quad. Digital TBC, compact Quad used in studios and remote trucks.

*Bosch Fernseh
**BCM-40 (1970) Solid state, analog TBC.

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, Digital Betacam 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.


ee also

* Videotape
* Contrast with Helical scan recording

External links

* [http://www.lionlamb.us/quad/theory.html Video systems theory] , with expanded information on the history of 2 inch Quad.
* [http://www.lionlamb.us/quadpark.html Quadruplex Park, Museum of 2 inch Quad VTRs] .
* [http://www.ev1.pair.com/edsel/edselshow1.html "The Edsel Show"] was the first TV entertainment program delayed for the West Coast on videotape.
* [http://web.archive.org/web/20040603152849/http://www.tvhandbook.com/History/History_recording.htm The History of Recording Technology] , with a section with pictures on 2 inch Quad and Ampex's development and introduction of it.
* [http://www.labguysworld.com/VTR_BirthOf.htm The Birth of Video Recording] .
* [http://www.televisiontape.tv Promotional kinescope] extolling the benefits of producing commercials on videotape instead of film.
* [http://lost-british-television.blogspot.com/ Blog describing many missing UK Television programmes] .
* [http://www.cedmagic.com/history/ampex-commercial-vtr-1956.html CED Magic's page on 2" Quad] .
* [http://www.novia.net/~ereitan/rca-nbc_firsts.html Color Television History] page about early Color VTR.
* [http://www.broadcasting101.ws/colorvtr_1970.jpgBosch 2" VTR 1970] .
* [http://www.oldradio.com/archives/hardware/TV/RCA-TV.htm RCA VTRs] .
* [http://www.lionlamb.us/quad/rca.html RCA VTR details] .


*US patent|2866012 "Magnetic Tape Recording and Reproducing System", Ampex patent filed May 1955, issued December 1958.

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