Quadruplex videotape

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Quadruplex videotape

A reel of 2-inch quadruplex videotape compared with a miniDV videocassette
Media type	Magnetic tape
Encoding	NTSC, PAL
Developed by	Ampex
Usage	Video production

2-inch quadruplex videotape (also called 2″ quad video tape or quadraplex) was the first practical and commercially successful analog recording video tape format.^[1] It was developed and released for the broadcast television industry in 1956 by Ampex, an American company based in Redwood City, California.^[2] 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 (already used for audio recording) for use with television as well. By 1954 the television industry in the US was consuming more film stock than all Hollywood studios combined.^[3]

The term "quadruplex" refers to the use of four magnetic record/play heads mounted on a headwheel spinning transversely (width-wise) across the tape at a rate of 14,386 RPM^[4] (for 960 recorded stripes per second) for NTSC 525 lines/30fps-standard quad decks and at 15,000 RPM (for 1,000 stripes per second) 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 7.5 or 15 in (190.5 or 381.0 mm) 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.^[5]

The quadruplex format employs segmented recording; each transversely recorded video track on a 2-inch quad videotape holds one-sixteenth (NTSC) or one-twentieth (PAL)^[6] of a field of interlaced video. (For NTSC systems, the math suggests 15 transverse head passes, each consisting of 16 lines of video, are required to complete one field.) 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.)^[7] 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.^[8]

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 (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 can play back both low and high-band 2-inch quad tape.^[9]