WHAT IS D-VHS?
The DVD dust has settled, decks and discs are starting to appear
in the shops and you reckon it's safe to go out and spend some of that hard-earned
cash on new gear? Think again! DVD was just a dress rehearsal for an even
bigger revolution in AV technology that will focus on the facility to record,
as well as playback movies and TV programmes from digital terrestrial, satellite
and cable sources…
VHS has been with us for almost twenty-five years, which is
pretty good going for any home entertainment technology, wax cylinders, 78 and
45 rpm records barely made their quarter centuries before fading into
obscurity. VHS has been incredibly successful -- we still buy almost 3 million
machines in the UK each year, despite the market reaching saturation point in
the early 1990s -- but the system's many shortcomings are now becoming
painfully apparent as we move towards the much hyped new age of digital
broadcasting. So what is going to replace it?
But does this faithful old workhorse really need replacing?
Sadly yes, apart from picture quality being so awful, we're about to be
inundated by several hundred digital TV channels, broadcast from satellite and
terrestrial transmitters, or squirted into our homes by high capacity cable.
Poor old whiskery, wobbly VHS simply isn't up to the job, either in terms of
picture and sound performance or recording capacity. Over the past 25 years the
format has been continually updated and we've come to think of it as cutting
edge technology but the truth is, the basic principles of analogue helical-scan
video recording were devised back in the late 1950's and relatively little has
changed since then. Even the best and most recent machines cannot capture more
than half of the information contained in a basic 625-line analogue television
So what chance has it got with digital TV? Zilch! Remember,
digital TV broadcasting will be in widescreen with multi channel sound plus a host
of digital data services, including the all important electronic programme
guide (EPG), which will be essential for time-shifting programmes and
navigating the new channels.
At first glance recordable DVD would seem to be the natural
successor to VHS for home video recording. The technology is available but most
industry insiders agree that home recording systems are still two or three
years away, and that's only if the many and various copy protection issues are
resolved and the Hollywood studios give it their blessing. DVD has other, more
serious technical limitations that rule it out for direct off-air digital
recording, though it can't be written off altogether and home recording decks are
likely to make an appearance early in the next century.
For a while the cute little DVC format looked quite
promising, and it has the capacity to record digital data streams. It was
originally developed for use in camcorders, which use miniature tapes, but the
specification also allows for homedeck machines using larger cassettes (about
the size of a box of 'kitchen' matches) with a 3-hour recording capacity.
However, to date only Sony and more recently Panasonic have bothered to develop
DVC VCRs. They remain prohibitively expensive for the general consumer market
(£2500 to £3300) and are principally aimed at serious and semi-pro video
movie-makers. DVC picture quality is significantly better than standard VHS,
but so too was Super VHS. That flopped because there was no pre-recorded
software and yielded only marginal performance improvements on most ordinary
TVs. DVC suffers from a similar lack of software and like Super-VHS, the
picture quality can only be appreciated on home video recordings. However its
main shortcoming is not any technical limitation but consumer inertia.
Persuading consumers to ditch their VHS video recorders and
software is going to be extremely difficult, particularly as many VCR owners
have amassed large collections of tapes. JVC, as the inventors and licensors of
the VHS format have been acutely aware of the difficulties for some time, they
also have more to loose than most when eventually the format fizzles out, as
inevitably it must. It's not surprising they have been working longer and
harder than anyone else to develop a twenty-first century replacement for VHS.
Super VHS was the first serious attempt to move the format
forward, JVC realised right from the start that any new system must be
backwards compatible with standard VHS. S-VHS did reasonably well in Japan and
one or two other areas but it never gained sufficient momentum to have an
impact on the world market.
JVC dallied briefly with another high performance analogue
sub-format in the late 1980s, called W-VHS (the W stood for widescreen). A few
prototypes were shown at trade exhibitions and again, it had some success in
Japan but it has sunk into relative obscurity. By the early 1990 it was
becoming obvious that analogue broadcasting and recording technologies were
heading up a blind alley. Rapid advances in digital processing -- spurred on by
developments in broadcasting and the computer industry -- were starting to have
an impact on all forms of audio and video home entertainment technology.
DIGITAL OR DATA?
And so it was in April 1995 JVC announced to the world that
the specifications for a new recording system, known as D-VHS, had been agreed
with leading consumer electronics manufacturers including Hitachi, Matsushita
and Philips. JVC wisely carried out
most of the initial research and development, and the subsequent negotiations
with other companies took place discretely behind closed doors. It was a shrewd
move and they managed to avoid almost all of the arguments and disputes that
have bedevilled recent format launches.
Nevertheless D-VHS hasn't been without its birth pangs, as
we'll see later on. However, the first real hurdle was the D-VHS name and this
caused immediate confusion. Everyone assumed it meant digital -- even some JVC
personelle referred to it as such in the early days -- but the official line
then, and now, is that it stands for 'data'. This is an important distinction
for marketing people; it frees the format from an overly close association with
home entertainment and opens the door for a tie in with the wider world of
The first and arguably the most important feature of the new
format is that it is one hundred percent backwards compatible with standard
VHS. In other words all D-VHS decks will be able to replay analogue VHS
cassettes -- even old tapes with mono sound -- and that includes Super VHS
recordings as well. Needless to say D-VHS recordings will not play back on
ordinary VHS (or S-VHS) video recorders, but we'll say it anyway as somebody is
bound to ask…
JVC engineers and designers realised right from the
beginning that backwards compatibility was essential if the format was to
succeed, but it has imposed some strict limitations on the design of the tape
cassette. It should therefore come as no surprise to learn that a D-VHS
cassette looks identical to a standard VHS tape. In fact the only visible
differences will be the sticky label and a small ident hole on the underside.
The tape itself is a high performance ferric oxide formulation, identical to
that used in S-VHS cassettes. That means cassettes are going to be a little
dearer than normal VHS tapes, though not by much. To give you some idea, a
typical 3-hour S-VHS cassette currently sells for around £10, that's three or four
times as much as a bog standard VHS E-180 but a lot less than a 3-hour DVC
cassette, say, which will set you back around £40. JVC are working on special
length D-VHS tapes, the standard item is likely to be a 5 hour (DF-300) tape
and even longer ones are in the pipeline.
The downside of backwards compatibility is that we'll be
stuck with clunky cassettes that rattle and take up far too much room for the
next quarter of a century, assuming of course that the format takes off.
However, it does means that D-VHS equipment is going to be a lot cheaper to
manufacture and to buy. Unlike virtually all new AV formats we won't have to
wait for the economies of scale to kick in and bring down the price of
mechanical components. They're almost always the most costly element in any
piece of AV equipment. Inside every D-VHS deck will be a more or less standard
VHS deck mechanism, almost nothing needs to be changed.
The only relatively minor difference will be the layout of
the head drum, two sets of video heads are needed to read both analogue and
digital data. Some additional electronics is required to process the two signal
streams, the analogue half is entirely conventional. Digital processing
circuitry will add to the cost but it involves mostly off the shelf microchips
and comparatively little new technology has had to be developed.
The first D-VHS video recorders have recently gone on sale
in the US for less than $1000 (around £750). If all goes well the first
machines that will be sold in the UK are likely to cost under £800; prices
should fall quickly to £500 or less if sales are brisk. We can safely assume
that first generation D-VHS video recorders will look like, and work like the
VHS video recorders we're familiar with now, but that's where the similarities with
the old system begin and end, and the cue for a grand tour of the
The first and most important feature -- apart from being
able to play old VHS tapes -- and the one that ties it in with digital
broadcasting, is bitstream recording. That's another way of saying that D-VHS
is capable of recording and replaying digital data, as it comes from the
satellite or TV transmitter, without the need for any additional signal
processing. That may not sound very important but until recently it simply
wasn't possible without recourse to compression, or data overflow, meaning that
information is lost when the recording is replayed. In fact D-VHS is well
within the ballpark for current MPEG 2 digital broadcasts which will normally
be transmitted at between 3 to 10 megabits per second. D-VHS has a fixed data
input rate of 14.1 Mbits/sec. That is significantly faster than DVD, which can
currently manage to process only 3.7Mbits/sec of compressed data, and another
reason why D-VHS is better suited to digital TV recording.
To put some flesh onto those numbers it means that a
standard 5-hour D-VHS tape will have a capacity of almost 32 gigabytes, JVC are
fairly confident they'll have a 7 hour tape (DF-420) before long, with a data
capacity of 44.7 gigabytes. That's equivalent to more than 65 CDs or CD-ROMS,
or 10 DVDs. A single D-VHS tape can hold three full-length movies -- with room
to spare -- in high quality MPEG 2 video, with accompanying multi-track digital
soundtracks. If the data rate is reduced, to accommodate MPEG-1 compressed signals,
the capacity of a 7-hour tape is increased to 21 hours of S-VHS quality
material or a staggering 49 hours of
VHS type recordings. Before you get too excited it is unlikely this facility
will be of any use for recording analogue TV transmissions as D-VHS equipment
is designed to record digital data streams, though there's no technical reason
why D-VHS VCRs couldn't be used with built-in or external analogue to digital
There are other, even more interesting possibilities. With
so much capacity available a D-VHS recorder will be able to record a complete
digital multiplex. A multiplex is a
group of channels, the number can vary according to how the broadcaster
organises the data bit rate, but it could mean a D-VHS VCR recording up to six
TV channels simultaneously. That could be six separate TV stations or six
camera views of a football match. As the recordings are made simultaneously the
viewer will be able to switch between cameras at any point during the match.
The channels could be part of an interactive program or even different plot
lines in a drama or movie.
Yet another development that D-VHS developers are actively
considering is 'burst transmission'. The technology has been conceived by a US
company called EMC3. They are planning to introduce a near video on demand
service using a system called electronic data delivery (EDD). At the heart of
EDD is a highly efficient video compression system that can squeeze 100 minutes
of MPEG 2 video data into a 'burst' of data, lasting just five minutes.
Specially adapted D-VHS recorders will capture the burst and replay the data at
a much slower speed, so the movie appears in real time. It's early days yet but
initial reports suggest the quality should be comparable with S-VHS.
JVC have also got their eye on the computer peripherals
market, and in particular the potential for D-VHS as a mass storage medium. It
has already been dubbed the 'digital refrigerator'… It's faster and more cost-effective
than any current tape-based backup or archiving system, and it is a perfect
medium for storing downloaded bulk software from satellite data channels.
Numerous commercial and industrial applications are also being investigated but
for the moment we'll confine ourselves to the domestic environment
Bitstream recording has other important advantages. It does
away with the need for any complex processing, encoding or encryption prior to
the signals going on to the tape. Put another way, D-VHS is completely
transparent, it doesn't matter if the data contains sub data signals for
multi-channel AC-3 (Dolby Digital) 5.1 audio for example, or data for EPG or
teletext displays. Everything that comes from the satellite or ground based
transmitter ends up on the tape, and comes out the other end.
That's the theory but complications have already arisen in
the US where makers of first generation D-VHS machines have opted to
incorporate on-board digital satellite decoders. The problem is different
receivers use different decryption and compression routines and the signals
that are recorded on the tape may not be playable on other makes of D-VHS
On a more positive note it appears that some sort of
agreement has been reached concerning connections with other digital devices.
JVC and the other manufacturers currently launching hardware in the US, and
later this year in Europe, have decided to adopt the industry-standard IEE 1394
or 'FireWire' digital interface.
Enough speculation, time for some actual hardware. At the
time of writing just one D-VHS video recorder has actually reached the
marketplace, and it's only available in the US. The machine is question is the
JVC HM-DSR100, which went on sale last October and before you ask, no it is not
going to be sold in the UK, at least not in its current form. The reason for
that is this particular machine is an NTSC standard model, dedicated to digital
satellite TV operation, recording broadcasts from the American DISH Network digital
direct broadcast satellite (DBS) service.
The HR-DSR100 has a built-in DBS tuner and is sold with a
24-inch dish and LNB, the selling price is a not unreasonable $1000 dollars.
For the technically inclined it uses an 8-head recording system with four 19
micrometre DA4 head used for VHS/S-VHS recording. It has two FM audio heads,
and two further heads exclusively for digital data recording and playback. In
addition to all normal VCR functions it also contains a 'V-Chip' for parental
control. (This, you may recall allows the user to bar access to certain
programs, based on transmitted ratings and content codes).
The JVC machine is fitted with a high-speed data terminal, as
far as we're aware this is not a FireWire connection on first generation models
but JVC are apparently working on a plug-in adaptor that will make it
compatible with IEEE 1394 protocols. The DISH Network broadcast an electronic
programme guide (EPG) and this is fully supported by the DSR100, enabling users
to access detailed programme information and simplify timer programming. DISH
Network also supports what's known as 'browse' features, this includes
superimposing on-screen information relating to the current program, plus
what's on the other channels. This is basically text and graphics and it is
included in the datastream, and recorded on the tape, so it can be viewed
during playback as well. Installation
is supposedly very simple and this extends to the alignment of the dish, which
is set automatically by inputting the owner's 'zip' code (the equivalent of a
postcode). The unified multi-brand remote control handset is also interesting;
it emits both infra-red (for close range) and UHF signals, so it can control
the VCR and a TV from a distance of up to 100 feet.
Whilst we're on the subject of the US market, Hitachi and
Thomson have also announced they'll be launching D-VHS equipment in the near
future. Hitachi models will also be sold under the RCA brand name. Both OEM manufacturers
are reported to be aiming for a $600 price point for their machines. Matsushita,
the parent company of Panasonic and JVC are reported to have an integrated
D-VHS video recorder and satellite decoder in development but as yet we have no
news of any US or European launches. Toshiba are the only company to have said
publicly they have no immediate plans to follow JVC's lead, citing the current lack
of support from broadcasters and the cost of production.
Here in the UK we can expect to see the first D-VHS video
recorder in the shops this autumn. The DVR-1000 is being made by Philips and
the target price will be £799.99. Unfortunately Philips are being fairly cagey
about what the machine will be capable of and the final specification,
suggesting that it is still being fine tuned. What we do know so far is that
it's going to be a stand-alone unit, without an on-board satellite decoder, and
it will be compatible with Philips own set-top digital boxes. The analogue
portion of the deck appears to be entirely conventional and is based around one
of their Turbo Drive mechanisms. Analogue features should include Video Plus+,
NICAM with stereo hi-fi sound plus a full range of replay speeds. The D-VHS
facilities are going to take full advantage of the format's outstanding tape
navigation features, using simple on-screen displays.
Since the DVR-1000 is going to have to be able to record and
play back existing PAL analogue tapes there are some minor differences between
this machine and its US counterparts. The principle one concerns the tape head
drum, which will operate at two speeds. When recording and replaying analogue PAL
recordings it spins at 1500rpm, but when it is in the digital mode it speeds up
to 1800rpm, in accordance with the D-VHS specification. Since the machine doesn't
have any built-in decoding facilities it won't have any EPG functions as such --
that will be the responsibility of the set top decoder and TV to which it is connected.
However, the machine will be able to make timed shift recordings using EPG
control signals, these will be sent to the machine via its digital interface. Just
before we went to press Philips confirmed that it would be using the
industry-standard FireWire interface on the DVR-1000. That should go some way
towards avoiding the connectivity problems encountered in the US, though it is
by no means certain that other set-top box manufacturers will also fit a
FireWire socket. For the moment at least the DVR-1000 looks like it will mainly
be of interest to owners of Philips digital decoders and TVs.
BOX COPY 1 350
The similarity between standard VHS and D-VHS tape cassettes
and deck mechanisms extends to the way information is physically recorded on
the tape. On both systems it is laid down as a series of diagonal tracks by a
pair of tape heads on a spinning head drum. Head drum speed on US models is
1800rpm. The linear tape speed for NTSC standard definition (SD) D-VHS recording/playback
is 16.67 mm/sec, that compares with 23.39mm/sec on a standard PAL VHS video
recorder. Frugal tape consumption has made it a little easier for tape manufacturers
to increase running times, without resorting to radically new formulations and
super-thin base films. Tape tracking is taken care of by the conventional CTL
edge track system, which is common to all VHS formats. The rate at which data is recorded on the tape
is 19.14 Mbits per second though the actual main data input rate, from other
digital devices is 14.1Mbits/sec. The modulation system, used to record
information, goes under the name of SI-NRZI (non return zero inverted). Collectors
of technical trivia and party bores might also like to know that the data
stream employs a sync block lasting precisely 112 bytes with code shuffling
across 6 tracks, so now you know…
Of more immediate importance is the fact that stand alone
D-VHS video recorders will only have digital data inputs and outputs for
bitstream recording and playback. The implication of that is a D-VHS machine
will not have any on-board digital to analogue conversion facilities, so the output
will have to be piped to suitable decoders, to extract video and audio signals.
The intention is that it will hook up to a set-top digital receiver.
The latest news is that JVC have now unveiled a high
definition (HD) variant, which will be able to record pure HDTV signals. This
will meet the needs of future developments, including the proposed ATSC and DTV
systems currently under development in Japan and the US. The provisional specs
suggest that HD D-VHS machines will have a maximum data rate twice than of SD
D-VHS at 28Mbits/sec, with an anticipated recording time of 3.5 hours.
BOX COPY 2
WHAT DOES THIS MEAN TO DVD?
Is D-VHS a threat to DVD? That seems very unlikely, DVD has
always been promoted as a playback-only medium and whilst recordable DVD
systems have been developed, privately a lot of companies are dubious about its
potential as a replacement for the VCR as we know it today. One of the problems
is its inability to make bitstream recordings of digital terrestrial and
satellite transmissions. It would, in effect only be able to make compressed
recordings of a single channel, ruling out the multi-camera angle facility. It
would also have an impact on picture quality, nor would it be able to capture
the sub-data information, needed to make effective use of extra facilities,
like the electronic program guide. DVD's future lies with cheap and abundant
pre-recorded software, if recordable systems do appear -- and that is still
open to debate -- then they're more likely to be viewed as a simple time-shift mechanism
for terrestrial programmes. However, a far more likely scenario is that
recordable DVD will evolve in to a computer peripheral (DVD-RAM), and
development is well under way with the first PC-sized player/recorders due to
be launched in the next few months.
BOX COPY 3
WORKING IN THE DIGITAL DOMAIN
One of the reasons we're going to need a technology like
D-VHS is the sheer number of TV channels that will shortly become available. At
the moment, with just five terrestrial and a dozen or so satellite stations we
can just about get by with a simple VHS video recorder. It also helps that
there's often only one or two programmes worth watching… D-VHS has the
capability of recording several channels simultaneously. Whether or not the
choice will improve with 100 or more channels on offer remains to be seen, but
the point is digital broadcasting is a whole new ball game.
Firstly there is the question of digital picture quality, it
has the potential to be better than current analogue TV, and D-VHS is currently
the only system able to record TV programmes in broadcast quality. In other
words recordings should be virtually indistinguishable from the off-air
picture. However, the biggest impact will be the change in picture aspect
ratio, from 4:3 to 16:9, and that does demand a more sophisticated recording
system. At the moment analogue VHS can only record widescreen transmissions in
letterboxed form, or by using anamorphic compression. In the first instance
there is a significant reduction in picture quality, and in the case of
anamorphic broadcasts, there won't be any, at least not from digital satellites
and in any case it requires specialised encoding/decoder circuitry.
D-VHS is also the only viable solution when it comes to
making use of the extra facilities available from digital broadcasters, namely
the electronic programme guide. That's because D-VHS has the capacity to record
the whole datastream, which will include the text and visuals that go to make
up the EPG. It will be like having access to an on-line listings magazine, but
one that's tied into the VCRs timer. You'll be able to read reviews, a potted
synopsis and any other information the broadcaster cares to include; this can
be categorised according to your tastes. If you like what you see, all you will
have to so is press a single button to program the timer.
BOX COPY 4
KIT OR CLEVER FUNCTIONS?
It's easy to wax lyrical about the future possibilities but
the fact is we're still at the very early stages of development and no-one
really knows what will eventually be on offer. There are going to be plenty of
growing pains too, and already the US experience is throwing up some unexpected
problems, concerning the compatibility of tapes recorded on different makes of
machine, and the lack of standardisation between the various types of
connections. Hopefully, by the time D-VHS arrives here the plugs and sockets
will be sorted out, and the FireWire digital interface is almost certainly
going to be the de-facto digital connection, but what other facilities will be
built in? Again, looking at the emerging American market an on-board digital
satellite receiver seems a likely prospect but the situation is a little more
complicated in Europe and the UK. We will have terrestrial digital broadcasts
to contend with and it is still uncertain when there will be a single decoder
box capable of handling both satellite
and terrestrial signals. Then there's the problems concerning conditional
access, interoperability and smart cards. In short, early adopters can expect a
bumpy ride, and anyone considering buying a first generation D-VHS video
recorder can look forward to early obsolecence.
R. Maybury 1998 3006