HOW THEY WORK : “The Video Home System – VHS”

The Video Home System (better known by its abbreviation VHS) is a consumer-level video standard developed by the Japanese company, JVC, and launched in 1976. It was first marketed to the public on October 1, 1977. During the close of the 1970s and the early 1980s, the home video industry was involved in the VHS vs. Betamax war, which VHS would eventually win. Advantages of VHS include longer playing time, faster rewinding and fast-forwarding, and a less complex tape transport mechanism. The open standard used for VHS technology allowed mass production without licensing costs. VHS would eventually succeed as the dominant home video format, surpassing others by the mid-1980s and into the 90s. However, in later years, optical disc formats began to offer better quality than video tape. The earliest of these formats, Laserdisc, was not widely adopted, but the later DVD (Digital Video Disc), format eventually did achieve mass acceptance and took over in film studios. By 2006, the United States of America had stopped releasing new movie titles in VHS format, opting for others such as DVD and Blu-ray Disc. On December 31, 2008, the last major United States supplier of pre-recorded VHS tapes, Distribution Video Audio Inc. of Palm Harbor, Florida, shipped its final truckload. Currently, most of the VHS tapes being produced are blank; these are meant for consumer use in dubbing or storage of their movies. Recording a VHS cassette holds a maximum of about 430 m of tape at the lowest acceptable tape thickness, giving a maximum playing time of about 3.5 hours for NTSC and 5 hours for PAL at “standard” (SP) quality. Other speeds include LP (long play) and EP/SLP (Extended play) which double and triple the recording time, for NTSC regions. These speed reductions cause a slight reduction in video quality (from 250 lines to 230 analog lines horizontal); also, tapes recorded at the lower speed often exhibit poor playback performance on recorders other than the one they were produced on. Because of this, commercial prerecorded tapes were almost always recorded in SP mode. VHS tapes have approximately 3 MHz of video bandwidth, which is achieved at a relatively low tape speed by the use of helical scan recording of a frequency modulated luminance (black and white) signal, with a down-converted “color under” chroma (color) signal recorded directly at the baseband. Because VHS is an analog system, VHS tapes represent video as a continuous stream of waves, in a manner similar to analog TV broadcasts. The waveform per scan-line can reach about 160 waves at max, and contains 525 scanlines from the top to the bottom of the screen in NTSC (480 visible). PAL variants have 625 scanlines (576 visible). In modern-day digital terminology, VHS is roughly equivalent to 333x480 pixels. JVC would counter 1985’s SuperBeta with VHS HQ, or High Quality. The frequency modulation of the VHS luminance signal is limited to 3 megahertz which makes higher resolutions impossible, but a HQ branded deck includes luminance noise reduction, chroma noise reduction, white clip extension, and improved sharpness circuitry. The effect was to increase the apparent horizontal resolution of a VHS recording from 240 to 250 analog (equivalent to 333 pixels from left-to-right, in digital terminology). The major VHS OEMs resisted HQ due to cost concerns, eventually resulting in JVC reducing the requirements for the HQ brand to white clip extension plus one other improvement. In 1987 JVC introduced the new format called Super VHS which extended the bandwidth to over 5 megahertz, yielding 420 analog horizontal (560 pixels left-to-right). eddie@afrowebs.com