[image] [image] The Video Home System, first released in 1976, better known by its acronym VHS, is a recording and playing standard for video cassette recorders (VCRs), developed by JVC (with some of its critical technology under lucrative licensing agreements with Sony) and launched in 1976. VHS officially stands for Video Home System, but it initially stood for Vertical Helical Scan, after the relative head/tape scan technique. Some early reports claim the name originally stood for Victor Helical Scan System.
VHS became a standard format for Consumer recording and viewing in the 1980s and 1990s after competing in a fierce format war with Sony's Betamax and, to a lesser extent, Philips' Video 2000. VHS initially offered a longer playing time than the Betamax system, and it also had the advantage of a far less complex tape transport mechanism. Early VHS machines could rewind and fast forward the tape considerably faster than a Betamax VCR since they unthreaded the tape from the playback heads before commencing any high-speed winding. Most newer VHS machines do not perform this unthreading step, as due to improved engineering, head-tape contact is no longer an impediment to fast winding.
VHS tapes have approximately 3 MHz of video Bandwidth, and a horizontal resolution of about 240 discernible lines per scanline . The frequency modulation of the luminance signal makes higher resolutions impossible within the VHS standard, no matter how advanced the recorder's Technology. The vertical resolution of VHS (and all other analog recording methods) is determined by the TV standard - a maximum of 486 lines are visible in NTSC and a maximum of 576 lines in PAL.
The video bandwidth is achieved with a relatively low tape speed by the use of Helical scan recording of a frequency modulated Luminance (black and white) signal, to which a Frequency-reduced "color under" chroma (hue and saturation) signal is added. In the original VHS format, audio was recorded unmodulated in a single (monaural) linear track at the upper edge of the tape, which was limited in frequency response by the tape speed. More recent hi-fi VCRs add higher-quality stereo audio tracks which are read and written by heads located on the same spinning drum that carries the video heads, frequency modulated to the unused frequency range in between the chroma and luma signals. These audio tracks take advantage of depth Multiplexing: since they use lower frequencies than the video, their magnetization signals penetrate deeper into the tape. When the video signal is written by the following video Head, it erases and overwrites the Audio signal at the surface of the tape, but leaves the deeper portion of the signal undisturbed. The excellent sound quality of hi-fi VHS has gained it some popularity as an audio format in certain applications; in particular, ordinary home hi-fi VCRs are sometimes used by Home recording enthusiasts as a handy and inexpensive medium for making high-quality stereo mixdowns and master recordings from multitrack audio tape.
Of course, for backward compatibility, hi-fi VCRs still write the linear audio track during recording, and can automatically read it during playback if the hi-fi audio is not present.
Some higher-end VHS and S-VHS VCRs once offered "audio dubbing" and "video dubbing" functions. These would move the tape past the heads and keep the video unchanged while recording new linear audio or keep the linear audio unchanged while recording new video, respectively. This was useful, for example, for laying a song over a previously edited-together montage of short video clips that were the same total duration as that song. Without the dubbing features, this task would've required the tape to be copied to another tape which would cause generational loss. (Due to the different ways in which linear and HiFi audio are recorded, these kinds of dubbing were not possible with the HiFi tracks). Another high-end feature was manual audio level control, which made the VHS HiFi format much more useful for high-quality audio-only recording purposes as discussed above. These advanced features are impossible to find on later-model VCRs due to the rise of digital video formats.
Another linear control track, at the tape's lower edge, holds pulses that mark the beginning of every frame of video; these are used to fine-tune the tape speed during playback and to get the rotating heads exactly on their helical tracks rather than having them end up somewhere between two adjacent tracks (a feature called tracking). Since good tracking depends on the exact distance between the rotating drum and the fixed control/audio head reading the linear tracks, which usually varies by a couple of micrometers between machines due to manufacturing tolerances, most VCRs offer tracking adjustment, either manual or automatic, to correct such mismatches.
The control track can additionally hold index marks. These are normally written at the beginning of each recording session, and can be found using the VCR's index search function: this will fast-wind forward or backward to the nth specified index mark, and resume playback from there. There was a time when higher-end VCRs provided functions for manually removing and adding these index marks - so that, for example, they coincide with the actual start of the program - but this feature has become hard to find in recent models.
Another variant is VHS-C (C for compact), used in some camcorders. Since VHS-C tapes are based on the same magnetic tape as full size tapes, they can be played back in standard VHS players using a mechanical adapter, without the need of any kind of signal conversion. The magnetic tape on VHS-C cassettes is wound on one main spool and uses a gear wheel to advance the tape; the wheel and spool can also be moved by hand. This development hampered the sales of the Betamax system somewhat, because the Betamax cassette geometry prevented a similar development.
There is also a JVC-designed component digital professional production format known as Digital-S or (officially) D9 that uses a VHS form factor tape and essentially the same mechanical tape handling techniques as an S-VHS recorder. This format is the least expensive format to support a pre-read edit. This format is most notably used by Fox for some of its cable networks.
Other formats such as 8mm video cassettes and MiniDV have emerged since, but these formats are by no means in complete competition with VHS. As these cassettes are much more compact in design - which also means the hardware to play and record the tapes has to be more compact than VHS, and therefore more expensive - they are much more suited to portable applications such as camcorders. 8mm tapes, introduced in the early 1980s, succeeded as a format for camcorders (both in the consumer, and to an extent, professional market), as VHS and Betamax camcorders were unsuitably large and heavy in comparison. MiniDV has largely replaced 8mm tapes as the De facto camcorder standard in more recent years as it is smaller still (some MiniDV camcorders being no larger than one's hand). In addition, it offers superior audiovisual quality, and the storage of data in digital format on tape makes for improved transfer and editing.
VHS still maintains the edge on cheapness for television home recordings, however - a VCR is still considerably cheaper than a DVD recording machine, although DVD has the edge on quality. This is the last field in which VHS technology is still ahead of its digital rival, though.
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