page_title: VHS
section_title: Video recording
hierarchical_section_title: VHS / Recording process / Video recording
caption_attribution_description: English: Medion MD8910 - VHS Helical scan tape head, inner view
context_page_description: VHS is a standard for consumer-level analog video recording on tape cassettes. Developed by Victor Company of Japan in the early 1970s, it was released in Japan on September 9, 1976, and in the United States on August 23, 1977.
  From the 1950s, magnetic tape video recording became a major contributor to the television industry, via the first commercialized video tape recorders. At that time, the expensive devices were used only in professional environments such as television studios and medical imaging. In the 1970s, videotape entered home use, creating the home video industry and changing the economics of the television and movie businesses. The television industry viewed videocassette recorders as having the power to disrupt their business, while television users viewed the VCR as a means to take control of their viewing experience.
  In the 1970s and early 1980s, there was a format war in the home video industry. Two of the standards, VHS and Betamax, received the most media exposure. VHS eventually won the war, dominating 60 percent of the North American market by 1980 and emerging as the dominant home video format throughout the tape media period.
context_section_description: The tape path then carries the tape around the spinning head drum, wrapping it around a little more than 180 degrees (called the omega transport system) in a helical fashion, assisted by the slanted tape guides. The head rotates constantly at 1798.2 rpm in NTSC machines, exactly 1500 in PAL, each complete rotation corresponding to one frame of video.
  Two tape heads are mounted on the cylindrical surface of the drum, 180 degrees apart from each other, so that the two heads "take turns" in recording. The rotation of the head drum, combined with the relatively slow movement of the tape, results in each head recording a track oriented at a diagonal with respect to the length of the tape. This is referred to as helical scan recording.
  To maximize the use of the tape, the video tracks are recorded very close together to each other. To reduce crosstalk between adjacent tracks on playback, an azimuth recording method is used: The gaps of the two heads are not aligned exactly with the track path. Instead, one head is angled at plus seven degrees from the track, and the other at minus seven degrees. This results, during playback, in destructive interference of the signal from the tracks on either side of the one being played.
  Each of the diagonal-angled tracks is a complete TV picture field, lasting 1/60 of a second (1/50 on PAL) on the display. One tape head records an entire picture field. The adjacent track, recorded by the second tape head, is another 1/60 or 1/50 of a second TV picture field, and so on. Thus one complete head rotation records an entire NTSC or PAL frame of two fields.
  The original VHS specification had only two video heads. Later models implemented at least one more pair of heads, which were used at (and optimized for) the EP tape speed. In machines supporting VHS HiFi (described later), yet another pair of heads was added to handle the VHS HiFi signal. Drums can contain 2, 4, 6 or 8 heads.
  The high tape-to-head speed created by the rotating head results in a far higher bandwidth than could be practically achieved with a stationary head. 
  VHS tapes have approximately 3 MHz of video bandwidth and 400 kHz of chroma bandwidth. The luminance (black and white) portion of the video is recorded as a frequency modulated, with a down-converted 
  "color under" chroma (color) signal recorded directly at the baseband. Each helical track contains a single field ('even' or 'odd' field, equivalent to half a frame) encoded as an analog raster scan, similar to analog TV broadcasts. The horizontal resolution is 240 lines per picture height, or about 320 lines across a scan line, and the vertical resolution (the number of scan lines) is the same as the respective analog TV standard (576 for PAL or 486 for NTSC; usually, somewhat fewer scan lines are actually visible due to overscan). In modern-day digital terminology, NTSC VHS is roughly equivalent to 333×480 pixels luma and 40×480 chroma resolutions (333×480 pixels=159,840 pixels or 0.16 MP (1/6 of a megapixel)), while PAL VHS offers the equivalent of about 335×576 pixels luma and 40×576 chroma (the vertical chroma resolution of PAL is not limited by any mechanism; SECAM is limited in resolution by a delay line mechanism).
  JVC countered 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 technically impossible even with the highest-quality recording heads and tape materials, but an 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 a new format called Super VHS (often known as S-VHS) which extended the bandwidth to over 5 mega
caption: The upper- and underside of a typical four-head VHS head assembly showing the head chips
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