Quadruplex Videotape

Quadruplex Videotape

2-inch quadruplex videotape (also called 2″ quad, or just quad, for short) was the first practical and commercially successful analog recording 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 broadcast television operations and television production, since the only recording medium available to the TV industry before then was film used for kinescopes, which was much more costly to utilize and took time to develop at a film laboratory.

Since most United States West Coast network broadcast delays done by the television 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 television programming for later airing on the West Coast. Broadcasters also sought a recording medium that was not as costly or time-consuming to edit and develop as film. Faced with these challenges, broadcasters sought to adapt magnetic tape recording technology (already in use for recording audio) for use with television as well.

The name "quadruplex" refers to the use of four magnetic record/reproduce heads mounted on a headwheel spinning transversely (width-wise) across the tape at a rate of 14,400 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 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 in (190.5 or 381.0 mm) per second for NTSC 525/30 video recording, or 15.625 in (396.875 mm) per second for PAL 625/25 video, 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 linear video editing.

A typical 4,800 ft (1,463 m) reel of 2 in (51 mm) quad tape holds approximately one hour of recorded material at 15 inches per second.

The quadruplex format employs segmented recording; each transversely recorded video track on a 2-inch quad videotape holds one-sixteenth of a field of video. This meant that 2-inch quad did not support "trick-play" functions, such as still, shuttle, and reverse or variable-speed playback. However, it was capable of producing extremely high-quality images containing about 400 horizontal lines of video resolution, 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 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 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.