A New Format - DIGITAL V.H.S.

This article was published in the June, 2000 edition of AUDIO VIDEO INTERIORS magazine Vol 12 / No. 6

It seems the future is getting closer every day. Now ...... a new digital, recording and playback medium known as Digital VHS (D-VHS). At first glance, it might appear like a high-end, professional format, but on the contrary, it is very much aimed at the consumer mass-market. It is capable of recording and playing back the full gamut of ATSC high-definition television (HDTV) digital images and sound, and all relatively inexpensively. Somewhat remarkably, not only does D-VHS record high-definition television broadcasts, but it can also offer a maximum recording time of 49 hours!!! Sound too good to be true ..... well, yes it is. It can't achieve both these remarkable feats at the same time .... but it can do them both nonetheless.

It seems like all-new technology, and it is. However, the basic mechanics of D-VHS recording is based on the conventional VHS mechanism, so the economic infrastructure, and the techniques deployed in the manufacturing process, are already well established worldwide. The evolving VHS technology has being perfected by most of the major electronic manufacturers for the past two decades. This situation is somewhat of an anomaly, as an established, wide-spread manufacturing base is in place, even before the new format is introduced to the general public. This means hardware prices can be kept to a minimum, and the prices are indeed similar to current, top-end VHS machines (competitive retailing allows currently available D-VHS models to be purchased for around $500, or even a little less).

Further more, D-VHS's ancestry makes true backwards compatibility possible. The success of this concept is overwhelming in the computer industry, and it is likely to work very well for Digital VHS as well. Yes, that right, these new D-VHS machines will play and record regular analog VHS tapes, in addition to the much higher-quality digital format. Most D-VHS units are capable of Hi-Fi VHS stereo sound as well. They will also play Super VHS tapes, but it seems not with the inherent quality of S-VHS, but rather with the image quality of conventional VHS (however, this may vary from model to model).

And this is no fly-by-night operation. Virtually all the major players are behind D-VHS, and indeed have been in preparation for its release for several years now. A conglomerate of manufacturers have set universal standards defining the technical specifications the for D-VHS format as far back as April 1996. And all this with a view to expanding the basic technology into other market areas, including a cheap, high-capacity, digital storage system.

D-VHS technology is made possible by a couple of clever innovations, namely Bit Stream Recording and FireWire. Simply put, the Firewire (or the IEEE 1394 interface) is the device that delivers the digital Bit Stream to and from the D-VHS system (more about FireWire in a moment). Firstly, Bit Stream Recording is a method for the direct recording on tape, of compressed, processed or encrypted signals as raw digital data, and outputting them in exactly the same raw state as they were originally input. In other words, the capture and reproduction of MPEG-2 signals.

MPEG-2 is a standard method of transmitting digital video and sound in a compressed format using less bandwidth than traditional analog methods (and most digital compression systems as well). It is the accepted standard for broadcasting all forms of digital television, including HDTV, and is also used by the current digital satellite broadcasters, like DirecTV / USSB and Dish Network. And MPEG-2 compression is used on DVD disks for movie presentations as well.

In the case of D-VHS, the Bit Stream or MPEG-2 recording unit does not incorporate functions like analog-to-digital conversion, digital-to-analog conversion, digital compression or decompression, and so forth. To reproduce video and audio signals, the Bit Stream data must go through further processing to convert the digital data to "displayable" video and audio signals. This means the Digital VHS unit can't do the whole job alone, and it must work in conjunction with other equipment connected between it and the viewing system (i.e. the television). In the realm of HDTV, this means a set-top, digital decoder box, or a HDTV set equipped with a full high-definition tuner. And in the world of broadcasting employing digital / analog crossover technology, namely the current satellite delivery systems like DSS, the additional equipment needed for Bit Stream processing is the satellite receiver / decoder box itself. This is basically how D-VHS is intended to be utilized, either for use in conjunction with HDTV broadcasting systems, or with current satellite broadcasting technology (the latter being capable of DVD-quality images and sound).

FireWire is the other magic component in the equation, used for moving the digital data around, both into, and also out of, the D-VHS machines. FireWire has an interesting history. It was originally developed by Apple Computer as a super high-speed serial bus. The technology was ahead of its time, and consequently took a while to catch on. In 1995, FireWire was accepted as a standard by the IEEE (Institute of Electrical and Electronics Engineers), henceforth called IEEE 1394. In the same year, FireWire was introduced on digital DV camcorders by Sony, which started the ball rolling. Now it is a major buzz word across several industries, including the wider computer and broadcasting industries.

Essentially, FireWire allows extremely high-speed transmission of high-volume, digitized audiovisual data (currently around 400 Mbit/sec with significant increases of 2 to 8 times this rate anticipated in the future). And all this through a single cable ..... (it has two individually shielded pairs for data, and two extra wires available for power, if required). FireWire (Apple Computer's original baby) is the same as the IEEE-1394 interface, which is also the same as "i.LINK" or "i.LINK 1394" by the Sony Corporation. So all these terms refer to the same thing. The full impact of the ubiquitous 1394 serial bus is yet to be seen.

So lets pause for a breath, and recap on the story so far. D-VHS is a new technology which is based on widespread, and highly popular VHS technology. D-VHS utilizes Bit Stream (or MPEG-2) recording technology, in conjunction with FireWire technology, which together allows the recording of compressed digital data such as digital broadcasts. Also, the format takes advantages of tape media which is an extremely cost effective method for storing high-volume digital data.

Here are the defining characteristics of the D-VHS format:

1. D-VHS enables MPEG-2, Bit Stream recording of digital broadcasts, in addition to analog recording of conventional broadcasts (such as NTSC, PAL etc.).

2. D-VHS uses the digital interface, IEEE 1394, poised for wide acceptance across the computer / broadcasting / electronics industries.

3. D-VHS takes advantage of the characteristics of tape as a medium to provide extremely large capacity digital data storage (approx. 44.4 Gigabytes per SF-420 cassette).

4. D-VHS maintains compatibility with conventional VHS for both recording and playback (i.e. it is backwards compatible, which gives it a significant marketing advantage).

There are 3 recording/playback Modes within the D-VHS system, namely HS, STD, and LS. Firstly, the HS (High Speed) mode is capable of recording high-definition (HD) digital images and multi-channel broadcasts. It works at a 28.2 Mbps data transfer rate. In the HS mode, the recording time on a single DF-300 cassette tape is 2.5 hours, and 3.5. hours on the longer DF-420 cassette.

The STD (Standard) mode is compatible with current digital satellite broadcasting, and is capable of recording and playing back "DVD-quality" digital images and sound. It works at a 14.1 Mbps data transfer rate. In the STD mode, the recording time on a single DF-300 cassette tape is 5 hours, and 7 hours on the longer DF-420 cassette. For the more technically minded, the tape speed is 16.67 mm/sec at a drum rotation speed of 1,800 rpm.

Thirdly, LS (Low Speed) is the mode which can allow a maximum recording time of that incredible 49 hours mentioned earlier!!! In this mode there are 4 selectable data rates: the lowest at 2.0Mbps (=49 hours recording), 2.8Mbps (= 35 hours recording), 4.7Mbps (21 hours recording), and 7.0Mbps (14 hours recording). To put these specs in better perspective, 2Mbps produces a picture quality better than standard VHS, and 4Mbps delivers better quality than Super VHS. Moreover, the image quality in HS mode is over 5 times that of current VHS. These differing rates also assure compatibility with a wide range of future applications, which D-VHS hopes to capitalize on in the future.

What about the recording medium itself i.e. the tapes or cassettes? Manufacturers have already released the D-VHS cassette type DF-300 (nominally 300 minutes = 5 hours in STD mode), and additionally, there is the DF-420 cassette (nominally 420 minutes = 7 hours in STD mode). The latter type is designed for extended recording time, and I'm told is poised for imminent release. The new D-VHS cassette looks very similar to the all too familiar VHS cassette in almost every respect, and you probably won't be able to tell them apart at a casual glance. However, there is a unique, underbelly indentation to distinguish D-VHS from regular VHS cassettes, and of course, the official S-VHS logo is stamped on the front of the cassette. The D-VHS cassette contains a grade of tape optimized for digital recording based on the existing S-VHS grade of tape. Right now, the price of a D-VHS tape (SF-300) seems to be around $11 to $15 each. It is expected that this price will drop as the market for the new format becomes better established (or to put it the other way around ..... the new format ought to take hold quicker if the tapes are cheaper).

Now to take a closer look at some models currently available (or soon to be released). The Hughes HDR-205 D-VHS and the JVC HM-DSR100 are out now (and can be purchased on the Internet), and the Panasonic PV-HD1000 started shipping in July. And Hitachi has two models, VTDX815A and HDS220S. The Hughes and Panasonic machines are similar in their basic function and capability. The Panasonic is designed to work with their set-top HDTV decoder box (TU-DST50, currently available for $1499), and is one of the very few such high-definition decoders on the market at the moment. The real magic begins when the Panasonic Digital VCR is linked to their HDTV set-top digital decoder via an IEEE 1394 digital interface (FireWire). This enables you to record and play back all 18 ATSC digital formats, including all variations of HDTV and SDTV with 1080 active lines of resolution that's over 4 or 5 times the resolution of the current VHS format! (That represents an increase in quality similar to that between 16mm and 35mm film.) And because it is capturing the data stream, it will even record all multiple programs, should a station choose to split the HDTV signal and deliver more than one program at the same time. And of course, all models also play and record regular VHS tapes. The PV-HD1000 even allows you to play tapes recorded in S-VHS mode (however, the picture quality of recordings in S-VHS mode is equal to that of VHS, and will not display with the increased S-VHS quality).

Because D-VHS is designed to be used with digital satellite systems, it is perhaps not surprising that JVC has married the two systems into their HM-DSR100 D-VHS Digital Satellite Recorder. It is essentially a D-VHS Recorder and a DISH Network Satellite Receiver (Echostar 5000) fused together into a single-unit design. The JVC concept allows digital Bit Stream Recording of DISH Network's MPEG-2 signal from a satellite dish, which is also part of the package. It then can play it back through a digital to analog converter (which is a normal function of any satellite decoder) to transform the original digital data into a video signal that will be recognizable by a regular household TV. But this unit does not support the highest quality reproduction, as it works in STD mode only, with a fixed bit rate of 14.1 Mbps (i.e. DVD-like quality). But of course, this is more than adequate until you buy that HDTV set and associated broadcast receiving system (antenna or dish, plus decoder).

I guess this would have to be the first domestic machine capable of recording Dolby Digital (AC-3) 5.1 channel digital sound. Of course, this is only possible when it is part of the original digital Bit Stream. The unit has a Dolby Digital (AC-3) output connector, which can be connected to an external decoder / amplifier to deliver full home-theater sound when playing back suitably encoded material. Similarly, any other sub-data signals incorporated within the program that is recorded, like the Dolby Digital sound described above, can be accessed later. For example, this might include text information, such as program guides, program notes, and similar information.

There are additional benefits of the single-unit design, for example, the unit's timer can be programmed directly from DISH Network's EPG (Electronic Program Guide), and therefore the clock is "auto-set by the satellite". This simplifies the timer-programming operation. And the external hook up for the system is no more complicated to set up than a regular VCR .... just plug in the antenna (or in this case, the dish cable), and then use another cable to plug the unit into the back of your T.V., and you are done. Unfortunately, the JVC lacks a true FireWire, IEEE 1394 interface. However, there is a high-speed data port which you can potentially adapt to make a connection to a PC, and such like. Also on the down side, the unit has a particularly noisy cooling fan, and does not provide an S-Video input ..... the price you pay in terms of features for this first-generation unit. Finally, JVC has made a stand alone unit (HM-DSR100RU), which does not include the dish antenna/decoder components, but retails for virtually the same price.

As we begin to invest more widely in the new Digital Television (DTV) technology (...... first that HDTV monitor, then the decoder box and a satellite or antenna receiving system .......), then I think the unique benefits of D-VHS will become apparent as the next logical step. The beloved VHS recorder of today, will quickly pale in the context of the new millennium. It will simply be unable to deliver the higher-quality images and sound we will soon learn to expect from our expensive new toys. But with some relief, the new generation of super-VCRs, will cost about the same as its "top-end" ancestors of today. And one might expect this price to drop with time, coming more in line with the popular mid-priced units of today. It seems the future is here, and the future looks bright.

Here is a list of companies that support the D-VHS format
(the 4 key D-VHS development companies are highlighted):

Daewoo Electronics Co., Ltd.
Funai Electric Co., Ltd.
Grundig
Hitachi Ltd.
JVC
LG Electronics Inc.
Matsushita Electric Industrial Co. Ltd.
Mitsubishi Electric Corporation
Philips Electronics
Samsung Electronics Co. Ltd.
Sanyo Electric Co. Ltd.
Sharp Corporation
Sony Corporation
Thomson Consumer Electronics
Toshiba Corporation

And Video Tape Makers producing the D-VHS cassette:

BASF Corporation
Fuji Photo Film Co., Ltd.
Hitachi Maxell, Ltd.
Konica Corporation
Sumitomo 3M Limited

Abbreviations used and their full meaning:

DTV = Digital Television (in all its forms)
HDTV = High Definition Television (a sub-set of DTV)
ATSC = Advanced Television Systems Committee (formed in 1987)
VHS = Video Home System (extremely popular, analog, home-video format)
S-VHS = Super VHS (improved quality, analog VHS)
D-VHS = Digital VHS (Digital evolution of the VHS format)
IEEE = Institute of Electrical and Electronics Engineers, Inc.
MPEG-2 = Motion Picture Experts Group (A standard method of transmitting digital video and sound in a compressed format using less bandwidth than traditional analog methods).
DSS = Digital Satellite System (the DirecTV / USSB satellite system - however, because of a trademark challenge the term is no longer used)
NTSC = National Television System Committee (who defined our current television system over 50 years ago)
PAL = Phase Alternating Line (A European television system used widely around the world)
S-Video = Divides a video signal into two components, color and luminance (black & white), to achieve a higher level of quality in transfer.
DVD = Digital Versatile Disk
VCR = Video Cassette Recorder

Peter Gray
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dp@petergray.org