II.

Analogue Recording

A.

Videotape

The techniques used to record images on videotape are similar to those used in sound recording and reproduction. Electrical signals from a television camera (or from a television camera via a television receiver) are stored as patterns of magnetized regions of iron oxide on magnetic tape. When the recorded tape is played back, the original signals are generated. These signals can then be disseminated by broadcast antenna or by cable to television receivers that translate the signals into images and sounds.

Videotape recorder/playback systems for domestic use are connected directly to a television receiver. Unlike motion picture film, videotape does not require processing, and so may be played back immediately. This makes possible the instant replay common to televised sporting events.

Audio signals have a bandwidth, or frequency range, of about 20,000 Hz and can be recorded on magnetic tape that passes over the record/playback head relatively slowly. Video signals, on the other hand, such as the signal that modulates the carrier wave of a television transmitter, have a bandwidth as high as 6 MHz and therefore require a much higher scanning speed to accommodate the 300-fold increase in information to be recorded or played back. The first magnetic video recorders, built in the early 1950s, relied on very fast tape speeds—up to 914 cm (360 in) per second—to record and reproduce images of an acceptable quality. Such recorders were not really practical, and the television industry continued to use motion picture film for recording live television programmes. These were referred to as kinescope recordings.

B.

Quadruplex

However, in 1956 a transverse scanning system of video recording and playback was developed by engineers of the Ampex company in the United States. In this system, called quadruplex, four record/playback tape heads are mounted on the circumference of a drum that rotates rapidly (14,400 rpm) at a right angle to the direction of tape movement. In this manner, the heads scan the video tracks on the tape with head-to-tape speeds equivalent to 3,810 cm (1,500 in) per second. The tape itself travels slowly: either 38 cm (15 in) or 19 cm (7 ½ in) per second. The sound track and the picture control track run linearly near the edges of the tape and are scanned by fixed heads. The picture control track generates signals that serve to adjust the speed of the rotating drum so that each head is aligned directly over the correct part of each recorded video track. The tape used in quadruplex systems is 50 mm (2 in) wide, and a 25-mm (1-in) length of tape contains 64 transverse tracks—enough for two frames of 525 lines each. This system came to be generally used in the television industry from the end of the 1950s.

C.

Helical Scan

In the 1960s a variant of this scanning principle was developed, called helical scan (or slant-track scan). At first this had a much slower head-to-tape speed than the quadruplex system, and the maximum bandwidth was only 3 MHz. Picture resolution was therefore inferior to that of quadruplex.

In helical scan, one or two record/playback heads are mounted on the circumference of a drum that rotates rapidly in the same direction as the tape transport. The tape is wrapped round the drum in a helical manner. The wrap angle (that is, the angle between initial and final contact with the drum) is anywhere from 180° to 360°, depending on the make of the recorder. The early helical scan systems, developed for domestic or professional use, employed tape widths of 13 mm (½ in) or 19 mm (¾ in) housed in tape cassettes.

At the end of the 1970s new models of helical scan recorders using 25-mm (1-in) tape and higher tape speeds were developed that could finally equal the quality of quadruplex machines. Manufacturers eventually standardized on two variants called “B format” and “C format”, with the latter proving more popular with television broadcasters as the new standard recording device that would displace quadruplex machines.

Video cassette recorders (VCRs) became relatively inexpensive by the early 1980s and were commonly sold for domestic use. Watching videos changed trends in television viewing: by the early 2000s the number of households in the UK owning a VCR had peaked at 87 per cent.

The first domestic videotape to be introduced onto the market was Betamax, by the Sony company in 1975; it was followed a year later by VHS, developed by JVC. For several years the two video formats (both 13 mm/½ in) were in competition until VHS finally became the industry standard in the 1980s. U-matic (¾ in), first developed by Sony in 1971, became a widely used format for corporate productions and ENG (electronic news gathering) in the 1970s and 1980s. Sony’s Betacam (13-mm/½-in) system, a professional counterpart of Betamax, later became the standard production format used in broadcasting after its launch in the early 1980s.

From the late 1980s onward, 8-mm (3/10-in) magnetic tapes also became much more common for use in domestic camcorders (combination video cameras and tape recorders). The smaller tape cassette size and long recording time of two hours made the 8-mm format attractive for use in lightweight, portable equipment.

Following their introduction, both the ½-in and the 8-mm formats were augmented by improved versions—Super-VHS and Hi8, respectively—that could handle greater bandwidths. The result was better picture definition or detail approaching that of professional video recorders.