Notes about the video format

SVHS, Super VHS, or Superior Video Home System, was developed by JVC to place so-called "broadcast quality" resolutions in the hands of home users. This is an extension to JVC's popular VHS format and uses video cassettes of the same size and shape. Initially, SVHS required specially manufactured videocassettes with a higher magnetic coercivity and a high precision housing to be used, but newer SVHS ET mechanisms allow standard high quality VHS cassettes to be used as SVHS media. This represents an improvement in the tolerance of SVHS mechanisms and the manufactured quality of VHS tapes today.

Before studying this document, you should make yourself thoroughly familiar with the VHS cassette format. The Audiotek document Notes about the VHS video format is an ideal lead-in. It discusses topics assumed to be well understood by the reader of this document, such as video signal parameters, the physics of the recording mechanism, television formats, and the mechanics of audio encoding.

Why use SVHS over VHS?

If you have ever watched a broadcast while recording it onto a VHS cassette, and watched the tape later, you have probably noticed that the finer details disappear. Also, if you have ever done any video editing, you have probably noticed that a copy of a VHS recording suffers a similar loss of detail when compared to the original recording. Indeed, if you make a copy of a copy, the quality is degraded again, and eventually there is no useful signal left.

SVHS retains 60% more of the detail present in the video signal over VHS, and maintains a horizontal resolution equivalent to that typically encountered in average television broadcasts. It achieves this by widening the separation between the modulation frequencies used for the chrominance and luminance present on the tape, and by increasing the bandwidth allocated to luminance by 60%. If luminance bandwidth alone were increased, crosstalk from the colour signal would reduce this level of improvement.

Because SVHS retains more information than VHS, it degrades at a significantly slower rate from generation to generation. So a copy of a copy suffers negligible loss of detail, and it will take many more cycles before the signal is no longer useful. SVHS is therefore the perfect format for doing video editing and for producing master tapes. SVHS VCRs also have the advantage that they can use VHS cassettes, making the vast library of existing VHS material accessible.

What is S-Video?

Because SVHS's quality is partially derived from an improved separation of the luminance and chrominance signals, it makes sense to keep these signals separated in the cables which join SVHS and other video equipment.

S-Video is the name given to the four pin mini-DIN connector used to carry this signal. Cables using this form of connection allow a higher quality video signal to be reproduced, as the filters and other circuitry used to combine and reconstitute composite video signals (RCA/BNC yellow connectors) degrade the signal from the high quality otherwise achievable by SVHS equipment. Audio is still transmitted on separate (white/red) RCA cables. S-Video signals can also be transmitted on some SCART cables, although equipment will need to be examined to ensure it is actually capable of using the separate luminance and chrominance paths.

An additional benefit can be gained from gold plated connectors and cables. Primarily, this gold plating increases the conductivity over the plug/socket interface, allowing better transmission of the signal. Clearly the benefit is greatly increased when both the socket and the plug are gold plated. An additional bonus is that gold plated connectors do not corrode, meaning that over time, the difference between gold plated connectors and untreated connectors becomes more marked.

Does SVHS play in a VHS VCR?

A high end hi-fi VCR will produce a watchable signal, although there will be luminance errors and artifacts. These artifacts will likely dominate or at least be unbearable on low to medium level equipment, but the only sure way to know is by experiment.

SVHS and VHS use the same colour modulation frequencies and bandwidths, so colour information is always correct. This is an interesting fact, because it means that SVHS does not improve on the colour resolution of VHS, except to reduce possible interference between chrominance in luminance. It should be noted however, while colour information is preserved, chrominance alone cannot generate a useful picture.

With regard to the luminance signal, the sync tip and peak white levels in an SVHS VCR are represented by higher frequencies than they would on a VHS tape, and the separation between these frequencies is greater. This usually results in disturbances or artifacts on a VHS VCR in the image as the signal on an SVHS cassette approaches the peak white intensity.

Audio on SVHS VCRs is recorded in identical fashion to VHS VCRs. This means that SVHS audio is always reproducable on VHS equipment. While not strictly necessary in the SVHS format, being a high end consumer format focused on delivering high quality, the linear audio track is also retained. This track is commonly used for audio dubbing, where a commentary or musical accompaniment is added after a recording has been made. The hi-fi stereo tracks are obviously to be preferred, but these signals cannot be altered once video has been laid down as they occupy the same area of the tape surface as the video signal.

What are the colour systems used by SVHS?

On SVHS, there is not a one to one correspondence between television colour systems and video formats. It is for this reason that a different convention is used to label the format of SVHS material than is used to label VHS. SECAM is effectively ruled out as a viable SVHS video format for reasons given in the Audiotek document Notes on the VHS video format.

NTSC/525 — NTSC M TV signals can be recorded onto SVHS NTSC/525 format videocassettes. The luminance horizontal resolution^[1] is improved from 220 lines, as found with VHS NTSC, to 400 lines. This is actually greater than the nominal figure quoted for NTSC broadcasts, which is 330 lines! The physical parameters of SVHS NTSC/525 are similar to VHS NTSC:

PAL/625 — PAL/SECAM B/G/I/D/K/H/L TV signals can be recorded onto SVHS PAL/625 format videocassettes. The luminance horizontal resolution¹ is improved from 250 lines, as found with VHS PAL, to 400 lines. This is equal to the nominal figure quoted for PAL broadcasts. The physical parameters of SVHS PAL/625 are similar to VHS PAL:

If VHS and SVHS are the same shape, how do you tell them apart?

Small holes are present on the underside of SVHS cassettes which allow them to be correctly recognised as such by SVHS equipment. VHS equipment will not recognise SVHS media as being any different from VHS media. In fact, it is possible to record VHS signals on SVHS cassettes, with somewhat better results than standard VHS cassettes.

Notes about Audiotek SVHS recordings

The catalogue of Audiotek SVHS video recordings is the ATKW catalogue. The catalogue includes all physically existing cassettes comprising the Audiotek SVHS library, whether they be Audiotek or third-party produced. Numbers are allocated consecutively starting at 001 as each cassette's contents are finalized. Cassettes may be freely deleted from the catalogue, and the number reallocated (or not) as required.

From 1999, most Audiotek master recordings have been made on SVHS cassettes. VHS is still sometimes used for archival work. SVHS recordings use a more detailed quality key than that used for VHS recordings, developed as a result of ironing out problems in the rather coarse, less descriptive and highly subjective scheme used for VHS recordings. A further scheme has been developed for use in digital video media, such as MiniDV (which was adopted as an acquisition format in 2000,) which places more emphasis on digital characteristics.

In order to categorize the quality of SVHS material, two classes of subjective charaterizations and one class of objective characterizations are employed. The two subjective classes quantify a number of specific characteristics which contribute to or subtract from quality. Those which contribute belong to the Perceived Gradation class, and those which subtract belong to the Perceived Degradation class. The objective measure involves quantifying the number of encode/decode steps the image has been through, both S-Video and composite: this measure is termed Objective Degradation.

Characteristics of Perceived Gradation are measured on the following subjective scale:

The characteristics of Perceived Gradation measured on this scale are:

Characteristics of Perceived Degradation are measured on the following subjective scale:

The characteristics of Perceived Degradation measured on this scale are:

Two characteristics are measured in the Objective Degradation category:

Audio characteristics are specified using the same key as given in Audiotek's Notes about the VHS video format. Additional characteristics are:

• Downmix for programmes where the original soundtrack has been algorithmically obtained from a five or six channel source.
• Compress where dynamic range has been compressed.
• Virtual indicates that a programme has had its audio post-processed for "virtual surround soundstage" two-channel reproduction. This is used in place of the Surround designation when such processing has occurred.

Accurate timings in hours, minutes and seconds are noted for all programmes in the Audiotek SVHS catalogue. Please refer to individual cassette manifests where these are available.

^[1]  Chrominance horizontal resolution is unchanged between VHS and SVHS at 40 lines.

^[2]  This mode is not well supported in typical SVHS equipment. Playback is typically supported—recording is not.

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Last updated: Sunday 28th May 2000