Technology Glossary. Bob Jensen at Trinity University · Click here to view (in this window) Bob Jensen's Technology and Technology in Education Glossary.
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Information related to the transatlantic power elite policy makers known as the Bilderberg Group.
1 9 3 0 s: 1930 United Kingdom: Start of Baird 30/12.5 experimental television service from the BBC Brookmans Park medium wave radio station in London: vision 356.3m.
Overview of color transmitting, voltage and frequency parameters of analog TV broadcast systems.
The Video Home System (VHS) is a standard for consumer-level use of analog recording on videotape cassettes. It was developed by Victor Company of Japan (JVC) in the 1970s. The 1950s began the era when magnetic tape video recording became a major contributor to the television industry, via the first commercialized video tape recorders (VTRs). At that time, the devices were used only in expensive professional environments such as television studios and medical imaging (fluoroscopy). In the 1970s, videotape entered home use, creating the home video industry and changing the economics of the television and movie businesses. In the 1980s and 1990s, at the peak of VHS' popularity, the home video industry was caught up in a series of videotape format wars. Two of the formats, VHS and Betamax, received the most media exposure. VHS would eventually win the war, and therefore succeed as the dominant home video format, lasting throughout the tape format period. In later years, optical disc formats began to offer better quality than video tape. The earliest of these formats, LaserDisc, was not widely adopted. However, the introduction of the DVD format to American consumers in 1997 began the market share decline of VHS. By 2008, DVD had achieved mass acceptance and replaced VHS as the preferred method of distribution. Often considered an important medium of film history, the influence of VHS on art and cinema was highlighted in a retrospective staged at the Museum of Arts and Design in 2013. In 2015, the Yale University Library collected over 2,500 VHS tapes, calling them "the cultural id of an era." After several attempts by other companies, the first commercially successful VTR, the AMPEX VRX-1000, was introduced in 1956 by AMPEX Corporation. At a price of US$50,000 in 1956, and US$300 for a 90-minute reel of tape, it was intended only for the professional market. Kenjiro Takayanagi, a television broadcasting pioneer then working for JVC as its vice president, saw the need for his company to produce VTRs for the Japan market, and at a more affordable price. In 1959, JVC developed a two-head video tape recorder, and by 1960 a color version for professional broadcasting. In 1964, JVC released the DV220, and would be the company's standard VTR until the mid-1970s. In 1969, JVC collaborated with Sony Corporation and Matsushita Electric (now Panasonic) in building a video recording standard for the Japanese consumer. The effort produced the U-matic format in 1971, which was the first format to become a unified standard. U-matic was successful in business and some broadcast applications (such as electronic newsgathering), but due to cost and limited recording time, very few of the machines were sold for home use. Soon after, Sony and Matsushita broke away from the collaboration effort, in order to work on video recording formats of their own. Sony started working on Betamax, while Matsushita started working on VX. JVC released the CR-6060 in 1975, based on the U-matic format. Sony and Matsushita also produced U-matic systems of their own. In 1971, JVC engineers Yuma Shiraishi and Shizuo Takano put together a team to develop a consumer-based VTR. By the end of 1971 they created an internal diagram titled "VHS Development Matrix". It established twelve objectives for JVC's new VTR. These included: The player must be compatible with any ordinary television set. Picture quality must be similar to a normal off-air broadcast. The tape must have at least a two-hour recording capacity. Tapes must be interchangeable between players. The overall system should be versatile, meaning it can be scaled and expanded, such as connecting a video camera, or dub between two players. Players should be affordable, easy to operate and have low maintenance costs. Players must be capable of being produced in high volume, their parts must be interchangeable, and they must be easy to service. In early 1972 the commercial video recording industry in Japan took a financial hit. JVC cut its budgets and restructured its video division, shelving the VHS project. However, despite the lack of funding, Takano and Shiraishi continued to work on the project in secret. By 1973 the two engineers had produced a functional prototype. In 1974, the Japanese Ministry of International Trade and Industry (MITI), desiring to avoid consumer confusion, attempted to force the Japanese video industry to standardize on just one home video recording format. Later, Sony had a functional prototype of the Betamax format, and was very close to releasing a finished product. With this prototype, Sony persuaded the MITI to adopt Betamax as the standard, and allow it to license the technology to other companies. JVC believed that an open standard, with the format shared among competitors without licensing the technology, was better for the consumer. To prevent the MITI from adopting Betamax, JVC worked to convince other companies, in particular Matsushita (Japan's largest electronics manufacturer at the time, marketing its products under the National brand in most territories and the Panasonic brand in North America, and JVC's majority stockholder), to accept VHS, and thereby work against Sony and the MITI. Matsushita agreed, primarily out of concern that Sony might become the leader in the field if its proprietary Betamax format was the only one allowed to be manufactured. Matsushita also regarded Betamax's one-hour recording time limit as a disadvantage. Matsushita's backing of JVC persuaded Hitachi, Mitsubishi, and Sharp to back the VHS standard as well. Sony's release of its Betamax unit to the Japanese market in 1975 placed further pressure on the MITI to side with the company. However, the collaboration of JVC and its partners was much stronger, and eventually lead the MITI to drop its push for an industry standard. JVC released the first VHS machines in Japan in late 1976, and in the United States in early 1977. Sony's Betamax competed with VHS throughout the late 1970s and into the 1980s. Betamax's major advantages were its cassette size, video quality, and earlier availability. Beta I was able to record one hour of programming at a tape-speed rate of 1.5 inches per second (ips) – its version of standard-play mode (SP). Originally, VHS recorded two hours of programming in SP at 1.31 ips, 0.656 ips for four-hour recording (LP or long play), and 0.437 ips for six-hour recording (EP or extended play). Betamax's smaller-sized cassette limited the size of the reel of tape, and could not compete with VHS' two-hour capability by extending the tape length. Instead, Sony had to slow the tape down to 0.787 ips (Beta II) in order to achieve two hours of recording in the same cassette size. This reduced Betamax's once-superior video quality to worse than VHS when comparing two-hour recording. Sony eventually released an extended Beta cassette (Beta III) which allowed Betamax to break the two-hour limit, but by then VHS had already won the format battle. It should be noted that the Beta I/II/III running times apply only to NTSC countries; in PAL and SECAM countries Beta's running time was similar to VHS, the quality at least as good, and the format battle was not fought on running time. The first VCR to use VHS was the Victor HR-3300, and was introduced by the president of JVC at the Okura Hotel on September 9, 1976. JVC started selling the HR-3300 in Akihabara, Tokyo, Japan on October 31, 1976. Region-specific versions of the JVC HR-3300 were also distributed later on, such as the HR-3300U in the United States, and HR-3300EK in the United Kingdom. The United States received its first VHS-based VCR – the RCA VBT200 on August 23, 1977. The RCA unit was designed by Matsushita, and was the first VHS-based VCR manufactured by a company other than JVC. It was also capable of recording four hours in LP (long play) mode. The United Kingdom later received its first VHS-based VCR – the Victor HR-3300EK in 1978. Quasar and General Electric would follow-up with VHS-based VCRs – all designed by Matsushita. By 1978, Matsushita alone produced just over half of all Japanese VCRs. The VHS cassette is a 187 mm wide, 103 mm deep, 25 mm thick (73⁄8 × 41⁄16 × 1 inch) plastic shell held together with five Phillips head screws. The flip-up cover that protects the tape has a built-in latch with a push-in toggle on the right side (bottom view image). The VHS cassette also includes an anti-despooling mechanism consisting of several plastic parts between the plastic spools, near the front of the tape (white and black in the top view). The spool brakes are released by a push-in lever within a 6.35 mm (¼ inch) hole accessed from the bottom of the cassette, 19 mm (¾ inch) inwards from the edge label. There is a clear tape leader at both ends of the tape to provide an optical auto-stop for the VCR transport mechanism. A light source is inserted into the cassette through the circular hole in the center of the underside when loaded in the VCR, and two photodiodes are located to the left and right sides of where the tape exits the cassette. When the clear tape reaches one of these, enough light will pass through the tape to the photodiode to trigger the stop function; in more sophisticated machines it will start rewinding the cassette when the trailing end is detected. Early VCRs used an incandescent bulb as the light source, which regularly failed and caused the VCR to erroneously think that a cassette is loaded when empty, or would detect the blown bulb and stop functioning completely. Later designs use an infrared LED which had a much longer lifetime. The recording media is a 12.7 mm (½ inch) wide magnetic tape wound between two spools, allowing it to be slowly passed over the various playback and recording heads of the video cassette recorder. The tape speed for "Standard Play" mode (see below) is 3.335 cm/s (1.313 ips) for NTSC, 2.339 cm/s (0.921 ips) for PAL—or just over 2.0 and 1.4 metres (6 ft 6.7 in and 4 ft 7.2 in) per minute respectively. As with almost all cassette-based videotape systems, VHS machines pull the tape from the cassette shell and wrap it around the inclined head drum which rotates at 1798.2 rpm in NTSC machines and at 1500 rpm for PAL. VHS uses an "M-loading" system, also known as M-lacing, where the tape is drawn out by two threading posts and wrapped around more than 180 degrees of the head drum (and also other tape transport components) in a shape roughly approximating the letter M. A VHS cassette holds a maximum of about 430 m (1,410 ft.) of tape at the lowest acceptable tape thickness, giving a maximum playing time of about four hours in an DF480 for NTSC and five hours in an E-300 for PAL at "standard play" (SP) quality. Other speeds include "long play" (LP), and "extended play" (EP) or "super long play" (SLP) (standard on NTSC; rarely found on PAL machines). For NTSC, LP and EP/SLP doubles and triples the recording time accordingly, but these speed reductions cause a slight reduction in video quality – from the normal 250 lines in SP, to 230 analog lines horizontal in LP and even less in EP/SLP. The slower speeds cause a very noticeable reduction in linear (non-hifi) audio track quality as well, as the linear tape speed becomes much lower than what is commonly considered a satisfactory minimum for audio recording. Both NTSC and PAL/SECAM VHS cassettes are physically identical (although the signals recorded on the tape are incompatible). However, as tape speeds differ between NTSC and PAL/SECAM, the playing time for any given cassette will vary accordingly between the systems. In order to avoid confusion, manufacturers indicate the playing time in minutes that can be expected for the market the tape is sold in. It is perfectly possible to record and play back a blank T-XXX tape in a PAL machine or a blank E-XXX tape in an NTSC machine, but the resulting playing time will be different from that indicated. To calculate the playing time for a T-XXX tape in a PAL machine, use this formula: PAL/SECAM Recording Time = T-XXX in minutes * (1.426) To calculate the playing time for an E-XXX tape in an NTSC machine, use this formula: NTSC Recording Time = E-XXX in minutes * (0.701) Some new Panasonic NTSC/ATSC recorders also include a XP mode which is not part of the official specification. It enables recordings at double the SP speed, such that a T-180 holds 1.5 hours. E-XXX indicates playing time in minutes for PAL or SECAM in SP and LP speeds. T-XXX indicates playing time in minutes for NTSC or PAL-M in SP, LP, and EP/SLP speeds. SP is Standard Play, LP is Long Play (½ speed, equal to recording time in DVHS "HS" mode), EP/SLP is extended/super long play (⅓ speed) which was primarily released into the NTSC market. Common tape lengths Tape label (nominal length in minutes) Tape length Rec. time (NTSC) Rec. time (PAL) m ft SP LP EP/SLP SP LP NTSC market T-20 44 145 22 min 44 min 66 min (1h 06) 31.5 min 63 min T-30 (typical VHS-C) 63 207 31.5 min 63 min (1h 03) 95 min (1h 35) 45 min 90 min (1h 30) T-45 94 310 47 min 94 min (1h 34) 142 min (2h 22) 67 min (1h 07) 135 min (2h 15) T-60 126 412 63 min (1h 03) 126 min (2h 06) 188 min (3h 08) 89 min (1h 29) 179 min (2h 59) T-90 186 610 93 min (1h 33) 186 min (3h 06) 279 min (4h 39) 132 min (2h 12) 265 min (4h 25) T-120 / DF240 247 811 124 min (2h 04) 247 min (4h 07) 371 min (6h 11) 176 min (2h 56) 352 min (5h 52) T-150 / DF300 316.5 1040 158 min (2h 38) 316 min (5h 16) 475 min (7h 55) 226 min (3h 46) 452 min (7h 32) T-160 328 1075 164 min (2h 44) 327 min (5h 27) 491 min (8h 11) 233 min (3h 53) 467 min (7h 47) T-180 / DF-360 369 1210 184 min (3h 04) 369 min (6h 09) 553 min (9h 13) 263 min (4h 23) 526 min (8h 46) T-200 410 1345 205 min (3h 25) 410 min (6h 50) 615 min (10h 15) 292 min (4h 52) 584 min (9h 44) T-210 / DF420 433 1420 216 min (3h 36) 433 min (7h 13) 649 min (10h 49) 308 min (5h 08) 617 min (10h 17) T-240 / DF480 500 1640 250 min (4h 10) 500 min (8h 20) 749 min (12h 29) 356 min (5h 56) 712 min (11h 52) PAL market E-30 (typical VHS-C) 45 148 22.5 min 45 min 68 min (1h 08) 32 min 64 min (1h 04) E-60 88 290 44 min 88 min (1h 28) 133 min (2h 13) 63 min (1h 03) 126 min (2h 06) E-90 131 429 65 min (1h 05) 131 min (2h 11) 196 min (3h 16) 93 min (1h 33) 186 min (3h 06) E-120 174 570 87 min (1h 27) 174 min (2h 54) 260 min (4h 20) 124 min (2h 04) 248 min (4h 08) E-180 259 849 129 min (2h 09) 259 min (4h 18) 388 min (6h 28) 184 min (3h 04) 369 min (6h 09) E-195 279 915 139 min (2h 19) 279 min (4h 39) 418 min (6h 58) 199 min (3h 19) 397 min (6h 37) E-210 304 998 152 min (2h 32) 304 min (5h 04) 456 min (7h 36) 217 min (3h 37) 433 min (7h 13) E-240 348 1142 174 min (2h 54) 348 min (5h 48) 522 min (8h 42) 248 min (4h 08) 496 min (8h 16) E-300 435 1427 217 min (3h 37) 435 min (7h 15) 652 min (10h 52) 310 min (5h 10) 620 min (10h 20) As manufacturers tend to err on the side of generosity when cutting tapes to length (for example, a 412ft "T-60" is in fact nearly 63 minutes long) in order to account for manufacturing errors and slight differences in deck spindle speed and spool-out, it is quite likely that some of these cassettes—for example, DF420 and E300, or E30 and T20—are actually manufactured to the same true length internally and are merely stamped with the same nominal length for sales purposes. Several other defined lengths of cassette entered mass production for both markets, but were either used only for professional duplication purposes (often pushing the limit of how much tape of a particular grade/thickness could fit into a standard cassette, in order to hold films that could not quite fit onto a shorter standard size without risking poorer quality or reliability by switching to a thinner grade), or failed to find popularity amongst home consumers because of a glut of tape length choices or poor value for money—e.g. T130/135/140, T168, E150, E270, and more besides. The recording process in VHS consists of the following steps, in this order: The tape is pulled from the supply reel by a capstan and pinch roller, similar to those used in audio tape recorders. The tape passes across the erase head, which wipes any existing recording from the tape. The tape is wrapped around the head drum, using a little more than 180 degrees of the drum. One of the heads on the spinning drum records one field of video onto the tape, in one diagonally oriented track. The tape passes across the audio and control head, which records the control track and the linear audio track or tracks. The tape is wound onto the take-up reel due to torque applied to the reel by the machine. The erase head is fed by a high level, high frequency AC signal that overwrites any previous recording on the tape. Without this step, the new recording cannot be guaranteed to completely replace any old recording that might have been on the tape. The tape path next 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 approximately 1800 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 1/60th of a second (1/50th on PAL) on the display. One tape head records an entire picture field. The adjacent track, recorded by the second tape head, is another 1/60th or 1/50th 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. 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 0.16MP (1/6 of a MegaPixel))., while PAL VHS offers the equivalent of about 335×576 pixels luma and 40×240 chroma (the vertical chroma resolution of PAL is limited by the PAL color delay line mechanism). 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 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 which extended the bandwidth to over 5 megahertz, yielding 420 analog horizontal (560 pixels left-to-right). Most Super VHS recorders can play back standard VHS tapes, but not vice versa. Because of the limited user base, Super VHS was never picked up to any significant degree by manufacturers of pre-recorded tapes. After leaving the head drum, the tape passes over the stationary audio and control head. This records a control track at the bottom edge of the tape, and one or two linear audio tracks along the top edge. In the original VHS specification, audio was recorded as baseband in a single linear track, at the upper edge of the tape, similar to how an audio compact cassette operates. The recorded frequency range was dependent on the linear tape speed. For the VHS SP mode, which already uses a lower tape speed than the compact cassette, this resulted in a mediocre frequency response of roughly 100 Hz to 10 kHz for NTSC;[frequency response for PAL VHS with its lower standard tape speed was somewhat worse. The signal-to-noise ratio (SNR) was an acceptable 42 dB. Both parameters degraded significantly with VHS's longer play modes, with EP/NTSC frequency response peaking at 4 kHz. Audio cannot be recorded on a VHS tape without recording a video signal, even in the audio dubbing mode. If there is no video signal to the VCR input, most VCRs will record black video as well as generate a control track while the audio is being recorded. Some early VCRs would record audio without a control track signal, but this was of little practical use since the absence of a control track signal meant that the linear tape speed was irregular during playback. More expensive decks offered stereo audio recording and playback. Linear stereo, as it was called, fit two independent channels in the same space as the original mono audiotrack. While this approach preserved acceptable backward compatibility with monoaural audio heads, the splitting of the audio track degraded the signal's SNR to the point that audible tape hiss was objectionable at normal listening volume. To counteract tape hiss, decks applied Dolby B noise reduction for recording and playback. Dolby B dynamically boosts the mid-frequency band of the audio program on the recorded medium, improving its signal strength relative to the tape's background noise floor, then attenuates the mid-band during playback. Dolby B is not a transparent process, and Dolby-encoded program material will exhibit an unnatural mid-range emphasis when played on non-Dolby capable VCRs. High-end consumer recorders took advantage of the linear nature of the audio track, as the audio track could be erased and recorded without disturbing the video portion of the recorded signal. Hence, "audio dubbing" and "video dubbing", where either the audio or video are re-recorded on tape (without disturbing the other), were supported features on prosumer linear video editing-decks. Without dubbing capability, an audio or video edit could not be done in-place on master cassette, and requires the editing output be captured to another tape, incurring generational loss. Studio film releases began to emerge with linear stereo audiotracks in 1982. From that point onward nearly every home video release by Hollywood featured a Dolby-encoded linear stereo audiotrack. However, linear stereo was never popular with equipment makers or consumers. 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, so that the high speed rotating heads remained exactly on their helical tracks rather than somewhere between two adjacent tracks (known as "tracking"). Since good tracking depends on precise distances 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 is also used to hold index marks, which were 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. At times, higher-end VCRs provided functions for the user to manually add and remove these marks — so that, for example, they coincide with the actual start of the television program — but this feature later became hard to find.[ By the late 1990s, some high-end VCRs offered more sophisticated indexing. For example, Panasonic's Tape Library system assigned an ID number to each cassette, and logged recording information (channel, date, time and optional program title entered by the user) both on the cassette and in the VCR's memory for up to 900 recordings (600 with titles). Around 1984, JVC added Hi-Fi audio to VHS (model HR-D725U, in response to Betamax's introduction of Beta Hi-Fi.) Both VHS Hi-Fi and Betamax Hi-Fi delivered flat full-range frequency response (20 Hz to 20 kHz), excellent 70 dB signal-to-noise ratio (in consumer space, second only to the compact disc), dynamic range of 90 dB, and professional audio-grade channel separation (more than 70 dB). VHS Hi-Fi audio is achieved by using audio frequency modulation (AFM), modulating the two stereo channels (L, R) on two different frequency-modulated carriers and embedding the combined modulated audio signal pair into the video signal. To avoid crosstalk and interference from the primary video carrier, VHS's implementation of AFM relied on a form of magnetic recording called depth multiplexing. The modulated audio carrier pair was placed in the hitherto-unused frequency range between the luminance and the color carrier (below 1.6 MHz), and recorded first. Subsequently, the video head erases and re-records the video signal (combined luminance and color signal) over the same tape surface, but the video signal's higher center frequency results in a shallower magnetization of the tape, allowing both the video and residual AFM audio signal to coexist on tape. (PAL versions of Beta Hi-Fi use this same technique). During playback, VHS Hi-Fi recovers the depth-recorded AFM signal by subtracting the audio head's signal (which contains the AFM signal contaminated by a weak image of the video signal) from the video head's signal (which contains only the video signal), then demodulates the left and right audio channels from their respective frequency carriers. The end result of the complex process was audio of outstanding fidelity, which was uniformly solid across all tape-speeds (EP, LP or SP.) Since JVC had gone through the complexity of ensuring Hi-Fi's backward compatibility with non-Hi-Fi VCRs, virtually all studio home video releases produced after this time contained Hi-Fi audio tracks, in addition to the linear audio track. Under normal circumstances, all Hi-Fi VHS VCRs will record Hi-Fi and linear audio simultaneously to ensure compatibility with VCRs without Hi-Fi playback, though only early high-end Hi-Fi machines provided linear stereo compatibility. Due to the path followed by the video and Hi-Fi audio heads being striped and discontinuous—unlike that of the linear audio track—head-switching is required to provide a continuous audio signal. While the video signal can easily hide the head-switching point in the invisible vertical retrace section of the signal, so that the exact switching point is not very important, the same is obviously not possible with a continuous audio signal that has no inaudible sections. Hi-Fi audio is thus dependent on a much more exact alignment of the head switching point than is required for non-HiFi VHS machines. Misalignments may lead to imperfect joining of the signal, resulting in low-pitched buzzing. The problem is known as "head chatter", and tends to increase as the audio heads wear down. The sound quality of Hi-Fi VHS stereo is comparable to the quality of CD audio, particularly when recordings were made on high-end or professional VHS machines that have a manual audio recording level control. This high quality compared to other consumer audio recording formats such as compact cassette attracted the attention of amateur and hobbyist recording artists. Home recording enthusiasts occasionally recorded high quality stereo mixdowns and master recordings from multitrack audio tape onto consumer-level Hi-Fi VCRs. However, because the VHS Hi-Fi recording process is intertwined with the VCR's video-recording function, advanced editing functions such as audio-only or video-only dubbing are impossible. A short-lived alternative to the hifi feature for recording mixdowns of hobbyist audio-only projects was a PCM adaptor so that high-bandwidth digital video could use a grid of black-and-white dots on an analog video carrier to give pro-grade digital sounds though DAT tapes made this obsolete. Some VHS decks also had a "simulcast" switch, allowing users to record an external audio input along with off-air pictures. Some televised concerts offered a stereo simulcast soundtrack on FM radio and as such, events like Live Aid were recorded by thousands of people with a full stereo soundtrack despite the fact that stereo TV broadcasts were some years off (especially in regions that adopted NICAM). Other examples of this included network television shows such as Friday Night Videos and MTV for its first few years in existence. The considerable complexity and additional hardware limited VHS Hi-Fi to high-end decks for many years. While linear stereo all but disappeared from home VHS decks, it was not until the 1990s that Hi-Fi became a more common feature on VHS decks. Even then, most customers were unaware of its significance and merely enjoyed the better audio performance of the newer decks. Several improved versions of VHS exist, most notably Super-VHS (S-VHS), an analog video standard with improved video bandwidth. S-VHS improved the horizontal luminance resolution to 400 lines (versus 250 for VHS/Beta and 500 for DVD). The audio-system (both linear and AFM) is the same. S-VHS made little impact on the home market, but gained dominance in the camcorder market due to its superior picture quality. The ADAT format provides the ability to record multitrack digital audio using S-VHS media. JVC also developed SVHS-ET technology for its Super-VHS camcorders and VCRs, which simply allows them to record Super VHS signals onto lower-priced VHS tapes, albeit with a slight blurring of the image. Nearly all Super-VHS camcorders and VCRs made today have SVHS-ET ability. Another variant is VHS-Compact (VHS-C), originally developed for portable VCRs in 1982, but ultimately finding success in palm-sized camcorders. The longest tape available for NTSC holds 60 minutes in SP mode and 180 minutes in EP mode. 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 adapter does not require a battery to function and is solely a mechanical adapter. It has an internal hub to engage with the VCR mechanism in the location of a normal full-size tape hub, driving the gearing on the VHS-C cassette. Also, when a VHS-C cassette is inserted into the adapter, a small swing-arm pulls the tape out of the miniature cassette to span the standard tape path distance between the guide rollers of a full-size tape. This allows the tape from the miniature cassette to use the same loading mechanism as that from the standard cassette. Super VHS-C or S-VHS Compact was developed by JVC in 1987. S-VHS provided an improved luminance and chrominance quality, yet S-VHS recorders were compatible with VHS tapes. Sony Betamax was unable to shrink that form any further, so instead they developed Video8/Hi8 which was in direct competition with the VHS-C/S-VHS-C format throughout the 80s, 90s, and 2000s. Ultimately neither format "won" and both continue to be sold in the low-end market (examples: JVC SXM38 and Sony TRV138). VHS single, also known as videotape single or Video 45s (a play on the term "45" when used to describe vinyl records) is a music single, using a standard-sized VHS cartridge. The format has existed since the early 1980s. In 1983, British synthpop band The Human League released the UK's first commercial video single on both VHS and Betamax as "The Human League Video Single". It was not a huge commercial success due to the high retail price of £10.99, compared to £1.99 for a vinyl single. The VHS single format gained higher levels of mainstream popularity when Madonna released "Justify My Love" as a video single in 1990 following the blacklisting of the video by MTV. U2 also released "Numb", the lead single from their 1993 album Zooropa as a video single. Despite the success of these releases, the video single struggled as its releases were relatively rare, the technology slowly being superseded first by CD Video (which proved unsuccessful due to the cost of capable LaserDisc players to play the video portion), music CDs with computer-accessible video files, then, by the early 2000s, by both DVD singles and CD+DVD releases. VHS tapes were however marketed to distribute music video compilations. W-VHS allowed recording of MUSE Hi-Vision analog high definition television, which was broadcast in Japan from 1989 until 2007. The other improved standard, called Digital-VHS (D-VHS), records digital high definition video onto a VHS form factor tape. D-VHS can record up to 4 hours of ATSC digital television in 720p or 1080i formats using the fastest record mode (equivalent to VHS-SP), and up to 40 hours of standard definition video at slower speeds. There is also a JVC-designed component digital professional production format known as Digital-S, or officially under the name 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 Sel-Sync pre-read for video editing. This format is most notably used by Fox for some of its cable networks. Shortly after the introduction of the VHS format, VHS tape rewinders were developed. These devices served the sole purpose of rewinding VHS tapes. Proponents of the rewinders argued that the use of the rewind function on the standard VHS player would lead to wear and tear of the transport mechanism. The rewinder would rewind the tapes smoothly and also normally do so at a faster rate than the standard rewind function on VHS players. However some rewinder brands did have some frequent abrupt stops, which occasionally led to tape damage. Some devices were marketed which allowed a personal computer to use a VHS recorder as a data backup device. The most notable of these was ArVid, widely used in Russia and CIS states. In the United States similar systems were manufactured by Corvus and Alpha Microsystems. Also available was Backer from Danmere Ltd. of England. VHS can record and play back all varieties of analog television signals in existence at the time VHS was devised. However, a machine must be designed to record a given standard. Typically, a VHS machine can only handle signals of the country it was sold in. Because some parameters of analog broadcast TV are not applicable to VHS recordings, the number of VHS tape recording format variations is smaller than the number of broadcast TV signal variations—for example, analog TVs and VHS machines (except multistandard devices) are not exchangeable between the UK and Germany, but VHS tapes are. The following tape recording formats exist in conventional VHS (listed in the form of standard/lines/frames): SECAM/625/25 (SECAM, French variety) MESECAM/625/25 (most other SECAM countries, notably the former Soviet Union and Middle East) NTSC/525/30 (Most parts of Americas, Japan, South Korea) PAL/525/30 (i.e., PAL-M, Brazil) PAL/625/25 (most of Western Europe, Australia, New Zealand, many parts of Asia such as China and India, some parts of South America such as Argentina, Uruguay and the Falklands, and Africa) Note that PAL/625/25 VCRs allow playback of SECAM (and MESECAM) tapes with a monochrome picture, and vice versa, as the line standard is the same. Since the 1990s, dual and multi-standard VHS machines have become more common. These can handle a variety of VHS-supported video standards. For example, regular VHS machines sold in Australia and Europe nowadays can typically handle PAL, MESECAM for record and playback, plus NTSC for playback only (provided the TV is capable of displaying NTSC's 525-line/30 fps standard). Dedicated multi-standard machines can usually handle all standards listed, of which some high end models can even convert the content of a tape from one standard to another on-the-fly during playback by using a built-in standards converter. S-VHS only exists in PAL/625/25 and NTSC/525/30. S-VHS machines sold in SECAM markets record internally in PAL, and convert to/from SECAM during record/playback, respectively. Likewise, S-VHS machines for the Brazilian market record in NTSC and convert to/from PAL-M. A small number of VHS decks are able to decode closed captions on prerecorded video cassettes. A smaller number still are able, additionally, to record subtitles transmitted with world standard teletext signals (on pre-digital services), simultaneously with the associated program. S-VHS has a sufficient resolution to record teletext signals relatively error-free without any special measures taken (to see them during playback, the TV simply has to be switched into its normal teletext mode), but VHS does not. The VHS logo was commissioned by JVC and introduced with the JVC HR-3300 in 1976. It uses the Lee font, designed by Leo Weisz. Although VHS was a popular delivery format for long-play content, VHS was also used to deliver short-play content, such as music videos, in-store videos and tutorials. VHS was also commonly included in various products and services – including exercise equipment, kitchen appliances, and even computer software. Corporations used the VHS format to deliver addresses made by company executives to regional offices. Manufacturers would send out VHS tapes to their service centers, to demonstrate how to repair a new product. And retail stores would play VHS tapes demonstrating a product on a television set, requiring a VCR that supported encore function replay or auto rewind play. VHS was the winner of a protracted and somewhat bitter format war during the late 1970s and early 1980s against Sony's Betamax format as well as other formats of the time. Betamax was widely perceived at the time as the better format, as the cassette was smaller in size, and Betamax offered slightly better video quality than VHS – it had lower video noise, less luma-chroma crosstalk, and was marketed as providing pictures superior to those of VHS. However, the sticking point for both consumers and potential licensing partners of Betamax was the total recording time. To overcome the recording limitation, Beta II speed (two-hour mode, NTSC regions only) was released in order to compete with VHS's two-hour SP mode, thereby reducing Betamax's horizontal resolution to 240 lines (vs 250 lines). In turn, the extension of VHS to VHS HQ produced 250 lines (vs 240 lines), so that overall a typical Betamax/VHS user could expect virtually identical resolution. (Very high-end Betamax machines still supported recording in the Beta I mode and some in an even higher resolution Beta Is (Beta I Super HiBand) mode, but at a maximum single-cassette run time of 1:40 [with an L-830 cassette].) Because Betamax was released more than a year before VHS, it held an early lead in the format war. However, by 1981, United States' Betamax sales had dipped down to only 25-percent of all sales. A debate continues between pundits over the cause of Betamax's loss. Some say – including Sony's founder Akio Morita – that it was due to Sony's licensing strategy with other manufacturers, which consistently kept the overall cost for a unit higher than a VHS unit, and that JVC allowed other manufacturers to produce VHS units license-free and keep cost lower. Others say that VHS had better marketing, since the much larger electronics companies at the time (Matsushita, for example) were on board with VHS. The VHS VCR was a mainstay in television-equipped U.S. living rooms for more than 20 years from its introduction. The home television recording market, as well as the camcorder market, has since transitioned to digital video-based recording. The introduction of the DVD format to American consumers in March 1997 triggered the market share decline of VHS. Though 94.5 million Americans still owned VHS format VCRs in 2005, market share continued to drop. Several retail chains in the United States and Europe announced they would stop selling VHS equipment in 2004, 2005, or 2006. The last film to be released on the VHS format in the United States was A History of Violence in 2006. In 2008, Distribution Video Audio Inc., the last major American supplier of pre-recorded VHS tapes, shipped its final truckload of tapes to stores in America. In the U.S., all major retailers no longer stock VHS home-video releases, focusing only on DVD and Blu-ray Disc technology. Additionally, all of the major Hollywood studios no longer issue releases on VHS. However, the horror film V/H/S/2 was released as a combo in North America that included a VHS tape in addition to a Blu-ray and a DVD copy on September 24, 2013. Despite the discontinuation of VHS in the United States, VHS recorders and blank tapes are still being sold at stores in other countries. As an acknowledgement of the continued usage of VHS, Panasonic announced the world's first dual deck VHS-Blu-ray player in 2009. The last standalone JVC VHS-only unit was produced on October 28, 2008. JVC, and other manufacturers, continued to make combination DVD+VHS units even after the decline of VHS. Despite the decline in both VHS players and programming on VHS tape, VCRs and VHS are still owned in some U.S. households. Those who still use or hold on to VHS do so for a number of reasons, including its alleged nostalgic value, its ease of use in recording, the fact that certain media still only exist in VHS format, their videos of personal events in their life are on VHS, or they are collectors of VHS releases. Expatriate communities in the United States also obtain video content from their native countries in VHS format. The Video CD (VCD) was created in 1993, becoming an alternative medium for video, in a CD-sized disc. Though occasionally showing compression artifacts and color banding that are common discrepancies in digital media, the durability and longevity of a VCD depends on the production quality of the disc, and its handling. The data stored digitally on a VCD theoretically does not degrade (in the analog sense like tape.) In the disc player, there is no physical contact made with either the data or label sides. And, when handled properly, a VCD will last a long time. Since a VCD can only hold 74 minutes of video, a movie exceeding that mark has to be divided into two or more discs. The DVD-Video format was introduced first, in 1996, in Japan, to the United States in March 1997 (test marketed) and mid-late 1998 in Europe and Australia. Despite DVD's better quality (typical horizontal resolution of 480 versus 250 lines per picture height), and the availability of standalone DVD recorders, VHS is still used in home recording of video content. The commercial success of DVD recording and re-writing has been hindered by a number of factors including: A reputation for being temperamental and unreliable, as well as the risk of scratches and hairline cracks. Incompatibilities in playing discs recorded on a different manufacturer's machines to that of the original recording machine. Shorter recording time: VHS tape has approximately 12 hours on a T-240/DF480 tape in EP, versus DVD which can record up to six hours on a single-layer disc. Compression artifacts: MPEG-2 video compression can result in visible artifacts such as macroblocking, mosquito noise and ringing which become accentuated in extended recording modes (more than three hours on a DVD-5 disc). Standard VHS will not suffer from any of these problems, all of which are characteristic of certain digital video compression systems (see Discrete cosine transform but VHS will result in reduced luminance resolution, which makes the picture look horizontally blurred (resolution decreases further with LP and EP recording modes). High-capacity digital recording systems are also gaining in popularity with home users. These types of systems come in several form factors: Hard disk–based set-top boxes Hard disk/optical disc combination set-top boxes Personal computer–based media center Portable media players with TV-out capability Hard disk-based systems include TiVo as well as other digital video recorder (DVR) offerings. These types of systems provide users with a no-maintenance solution for capturing video content. Customers of subscriber-based TV generally receive electronic program guides, enabling one-touch setup of a recording schedule. Hard disk–based systems allow for many hours of recording without user-maintenance. For example, a 120 GB system recording at an extended recording rate (XP) of 10 Mbit/s MPEG-2 can record over 25 hours of video content. Wikimedia Commons has media related to VHS. HowStuffWorks: How VCRs work The 'Total Rewind' VCR museum covering the history of VHS and other vintage formats VHSCollector.com: Analog Video Cassette Archive A growing archive of commercially released video cassettes from their dawn to the present, and a guide to collecting.
Phase Alternating Line (PAL) is a colour encoding system for analogue television used in broadcast television systems in most countries broadcasting at 625-line / 50.
A VHS cassette holds a maximum of about 430 m (1,410 ft.) of tape at the lowest acceptable tape thickness, giving a maximum playing time of about four hours in an.