Quadruplex videotape
2-inch quadruplex videotape was the first practical and commercially successful analog recording video tape format. The format uses magnetic tape and 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.
Since most United States network broadcast delays by the television networks at the time used kinescope film that took time to develop, the networks wanted a more practical, cost-effective, and quicker way to time-shift television programming for later airing in Western time zones than the expensive and time-consuming processing and editing of film. Faced with these challenges, broadcasters sought to adapt magnetic tape recording technology for use with television as well. By 1954 the television industry in the US was consuming more film stock than all Hollywood studios combined.
The term "quadruplex" refers to the use of four magnetic record/play heads mounted on a headwheel spinning transversely across the tape at a rate of 14,386 RPM for NTSC 525 lines/30fps-standard quad decks and at 15,000 RPM for those using the PAL 625 lines/25fps video standard. This method is called quadrature scanning, as opposed to the helical scan transport used by later videotape formats. The tape ran at a speed of either per second; 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 linear video editing.
The quadruplex format employs segmented recording; each transversely recorded video track on a 2-inch quad videotape holds one-sixteenth or one-twentieth of a field of interlaced video. This meant that 2-inch quad did not support "trick-play" functions, such as still, shuttle, and reverse or variable-speed playback. In fact, the quadruplex format could only reproduce recognizable pictures when the tape was playing at normal speed. However, it was capable of producing extremely high-quality images with a horizontal resolution of about 400 lines per picture height, and remained the de facto industry standard for television broadcasting from its inception in 1956 to the mid-1980s, when newer, smaller, and lower-maintenance videotape formats such as Type C videotape superseded it.
There were three 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 video tape recorder, and
- Super high-band, which used a pilot tone for better timebase stability, and higher coercivity tape.
History
Time-shifting of television programming for the Central, Mountain, and Pacific Time Zones by the networks in the 1950s using kinescope films was quite a rushed and perilous ordeal. This was because there was minimal time for the West Coast studios and operations of the major television networks at the time to receive video for the programming from the East Coast, to record it to kinescope films, and to develop the film to be sent via AT&T's network as well to the networks' local affiliate stations in the western US. This usually meant the kinescope was aired almost immediately after it came straight out of the developing equipment, still warm from the film dryer. These were referred to by the networks as "hot kines". By 1954, the networks used more raw film stock for kinescopes than all of the Hollywood film studios combined, spending up to $4,000 per half hour.Ampex, seeing the impracticality of prototype video tape recorders from Bing Crosby Enterprises and RCA, 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 -wide tape. Ampex decided that instead of having the tape move at high speed past a stationary head to record enough bandwidth for video, the head would be made to move rapidly across the relatively slow moving tape. This resulted in the Mark I using arcuate scanning, which consisted of a spinning disk with a face which contacted the tape. 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, 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 continued through the mid-1950s with the Mark II and Mark III prototype recorders. The Mark II was the first to use FM modulation to record the incoming video signal to the tape as an FM carrier modulated to the video input, resulting in a drastic improvement in video playback quality compared to the Mark I, which used AM modulation and resulted in quite poor & noisy video reproduction upon playback.
The Mark IV was the machine first publicly demonstrated at the National Association of Radio and Television Broadcasters convention in Chicago on April 14, 1956. After William Lodge of CBS finished his speech, the Mark IV replayed his image and words almost immediately, causing "pandemonium" among the astonished attendees. 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 Ampex took $2 million in orders for the machine in four days.
Ampex later released the first 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. The advertised price for the Ampex Videotape Recorder in late 1956 was $45,000.
In 1957, shortly after Ampex's introduction of the 2-inch quad format, RCA 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.
Ampex developed and released updated and improved models of their quad decks, beginning with the VR-1000B in mid-1959. At that time, Ampex advertised that some 360-plus VR-1000s had been sold worldwide, more than 250 in the U.S.—roughly 30 at each network, 100 by independent stations, and 20 by production companies. The second-generation VR-2000 appeared in 1964. followed by a scaled-down economy version, the VR-1200, in 1966 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, using conventional 120 volt single-phase household-type AC power to operate, rather than the 208 or 220 V three-phase AC power required by larger quad machines. RCA released later models of quad VTRs as well, such as the TR-22, TR-70, 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. 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. 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.
The engineers at Ampex who worked on the development of 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.
As two inch machines became more reliable, they began to see use in outside broadcast production. The massive machines required their own truck to house and were incredibly labour-intensive requiring considerable on site maintenance. Despite this, these machines allowed for OB video engineers to provide instant replays and generate opening sequences over which captions could be added.
Product models
Ampex
- VR-1000 FM Low band, three racks of tubes, monochrome. No timebase correction.
- VR-1000 "Allen" or "Allenized" update kits to color solid state, FM high band updateable, solid state servo system.
- VR-1001 VR-1000 with the transport vertical.
- VR-2000 Solid state, first color-capable quad VTR with high band. Optional Editec, Dropout compensation. Mark 10 head. Analog TBC.
- VR-1100E Solid-state VR-1000.
- VR-1195 VR1100 with many Ampex updates.
- VR-1200 Solid state, color high-band. Analog TBC. Optional Editec. Scaled-down economy version of the VR-2000.
- VR-3000 Portable VTR with a Mark 11 ball-bearing head. All-format VTR. Digital TBC was possible, but required extensive mechanical modifications to the basic unit. Battery- or line-powered.
- VR-3000B Portable VTR Improved version of VR-3000. Digital TBC was available as a plug-in accessory, and required no modifications to the basic unit. Improved batteries.
- AVR-1 Very fast VTR, vacuum columns, vacuum capstan, air transport. NTSC/PAL switchable. Analog TBC.
- ACR-25 Cart VTR, with two AVR-1 type decks.
- ACR-25B Cart VTR, ACR-25 with AVR-2 digital TBC.
- AVR-2 Digital TBC, compact Quad used in studios and remote trucks. Uses 110-volt single-phase AC.
- AVR-3 Last Ampex Quad, digital TBC. Vacuum capstan. Super high band.
The VR-2000 & VR-1200 used modules to correct the playback time base errors of the videotape.