S-VHS
Improved version of VHS From Wikipedia, the free encyclopedia
S-VHS (スーパー・ヴィエイチエス), the common initialism for Super VHS, is an improved version of the VHS (VHS standing for video home system) standard for consumer-level video recording.[1] Victor Company of Japan introduced S-VHS in Japan in April 1987, with their JVC-branded HR-S7000 VCR, and in certain overseas markets soon afterward. By the end of 1987, the first S-VHS VCR models from other competitors included the Hitachi VT-2700A, Mitsubishi HS-423UR, Panasonic PV-S4764, RCA VPT-695HF, and Toshiba SV-950. It has been standardized as IEC 60774-3 and IEC 60774-4.[2][3]
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An S-VHS tape | |
| Media type | Magnetic tape cassette |
|---|---|
| Encoding | PAL, NTSC, ADAT |
| Capacity | 9 hours in super long play (SLP) mode on T-180, 10 hours in PAL-LP with E-300 tape (up to 15h in PAL-EP machines) |
| Standard | 525 lines, 625 lines |
| Usage | Home video, home movie, educational, video production, professional digital audio |
| Extended from | VHS |
| Released | April 1987 |
Technical information
Summarize
Perspective
Like VHS, the S-VHS format uses a color under A modulation scheme.[4] S-VHS improves luminance (luma) resolution by increasing luminance bandwidth.[4] Increased bandwidth is possible because of the increased luminance carrier from 3.4 megahertz (MHz) to 5.4 MHz.[4] The luminance modulator bandwidth also is increased: in contrast to standard VHS's frequencies of 3.8 MHz (synch tip) to 4.8 MHz (peak white), S-VHS uses 5.4 MHz synch tip and 7.0 MHz peak white.[5][6] Increased luminance bandwidth produces a 60% improvement in luminance picture detail—a horizontal resolution of 420 vertical lines per picture height,[7] versus VHS's 240 lines. The often quoted horizontal resolution of "over 400" means S-VHS captures greater picture detail than even NTSC[4] analog cable and broadcast TV, which is limited to about 330 television lines (TVL).[8] In practice, when time-shifting TV programs on S-VHS equipment, the improvement over VHS is noticeable. Yet, the trained eye can easily spot the difference between live television and an S-VHS recording of it. This is because S-VHS does not improve other key aspects of the video signal, particularly the chrominance (chroma) signal. In VHS, the chroma carrier is both severely bandlimited and noisy, a limitation that S-VHS does not address. Lack of color resolution was a deficiency shared by S-VHS's contemporaries, such as Hi8 and ED-Beta – all of which were limited to 0.4 megahertz or 30 TVL resolution.[9]
In audio recording, S-VHS retains VHS's conventional linear (baseband) and high fidelity (Hi-Fi) – Audio Frequency Modulation (AFM) soundtracks. Some professional S-VHS decks, and high end domestic S-VHS VCRs[10] such as the Victor HR-Z1 can additionally record a pulse-code modulation (PCM) digital audio track (stereo 48 kHz), onto S-VHS tape along with normal video and Hi-Fi stereo and mono analog audio.
This is performed by using a high carrier frequency of 3 MHz for the digital audio with O-QDPSK (Offset Quadrature Differential Phase Shift Keying) modulation and PCM encoding[11][12][13] which is then recorded onto the same helical tracks as the video. This frequency is above those used for VHS Hi-Fi (1.7 MHz for the left channel, 1.8 MHz for the right channel) but below the luminance signal frequency for regular VHS of 3.4 MHz.[14][15][16] The digital audio stream has a bit rate of 2.6 Mbps.[17][18][19][20] O-QDPSK is based on QDPSK (Quadrature Differential Phase Shift Keying), also known as DQPSK (Differential Quadrature Phase Shift Keying), and is very similar to it, except O-QDPSK signals are free from zero crossing; the signals never cross the 0 voltage point. Instead they are above and below the 0 voltage point. This type of digital audio requires a bandwidth of 500 KHz. It is also possible for this audio channel to have a carrier frequency of 2 MHz.[21]
The bandwidth of S-VHS allows PAL recordings to contain Teletext data along with the normal video signal, which then can be displayed as an overlay of the conventional TV picture (though not on standard VHS machines). A suitably Teletext-equipped receiver/decoder (TV, PC card, etc.) displays the recorded Teletext data information as if the video were a television transmission being received at that moment.
Hardware
S-VHS video cassette recorders (VCRs) and cassette tapes are nearly identical in appearance and operation, and backward compatible with VHS. VHS VCRs cannot play back S-VHS recordings at all but can record onto an S-VHS tape in the basic VHS format.[22] Newer VHS VCRs, depending upon their specification, offered a feature called S-VHS quasi-playback or Super Quasi-Play Back, abbreviated to SQPB. SQPB lets basic VHS players view (but not record) S-VHS recordings, though reduced to the lesser VHS quality. This feature is useful for viewing S-VHS camcorder recordings that use either the full-size S-VHS videotape cassette or the smaller S-VHS-C videotape cassette.
Later model S-VHS VCRs offered a recording option called S-VHS ET, which allowed SVHS VCRs to record on VHS tape. S-VHS ET is a further modification of the VHS standards that permitted near S-VHS quality recordings on more common and less expensive basic VHS tapes. S-VHS ET recordings can be viewed on most SQPB-equipped VHS VCRs and S-VHS VCRs.
To get the most benefit from S-VHS, a direct video connection to the monitor or TV is required, ideally via an S-Video connector and/or S-Video enabled SCART.
Media
In order to take advantage of the enhanced capabilities of the S-VHS system, i.e., for the best recordings and playback, an S-VHS VCR requires S-VHS video tape cassettes.[4] These have a different oxide media formulation for higher magnetic coercivity. S-VHS video cassettes are sensed and identified by the video cassette recorder via a specific internal profile within a hole in the underside of the S-VHS video cassette body.
Videophiles were the first to theorize that since the only distinguishing feature of an S-VHS tape is a small 3 mm hole on the underside of the video cassette, it should be possible to use more common and inexpensive VHS tapes by duplicating that hole. However, S-VHS cassettes contain a higher grade and coercivity of tape stock to effectively record the higher video bandwidth offered by S-VHS.
S-VHS tapes can be used with VHS VCRs, but an S-VHS recording will not play back properly on a VHS VCR without SQPB (sound is usually reproduced correctly, but the picture quality will be poor).
S-VHS ET
JVC introduced an S-VHS ET (Super-VHS Expansion Technology) system on its S-VHS consumer decks, allowing the use of normal VHS tapes for S-VHS recording, by slightly modifying the S-VHS recording specs, while still retaining compatibility, so that S-VHS ET tapes could be played with non-ET S-VHS VCRs. In S-VHS ET mode, the recording circuit is altered with:
Use for digital audio
In 1991, Alesis introduced ADAT, an eight-track digital audio recording system that used S-VHS cassettes. An ADAT machine recorded eight tracks of uncompressed audio material in 16-bit (later 20-bit) resolution. The recording time was one-third of the cassette's nominal playing time, e.g., a 120-minute S-VHS cassette held 40 minutes of eight-track audio.
Studer produced the V-Eight (manufactured and sold by Alesis as the M20) [24] and the V-Twenty-Four digital multitrack recorders. These used S-VHS cassettes for 8-track and 24-track digital audio recording, at a significantly lower cost than their DASH reel-to-reel digital recorders. The videotape transports were made for Studer by Matsushita.
See also
References
External links
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