DAT IS HERE TO STAY - FOR A WHILE AT LEAST BUT IS IT RIGHT FOR YOU AND YOUR STUDIO? IS A DIGITAL RECORDING SYSTEM WHOSE MACHINES COME NO BIGGER THAN CASSETTE DECKS, AND WHOSE TAPES ARE CONSIDERABLY SMALLER, GOOD ENOUGH FOR PRO STUDIOS OR CHEAP ENOUGH FOR SMALL ONES?

IF YOU CAST your mind back to the July 1989 issue of Music Technology, you'll remember we looked into the technology behind a recent hi-tech revolution: Digital Audio Tape. In the ensuing eight months or so, there has been little change from the situation outlined then. A couple of new machines have appeared - and one that's about to appear is going to make DAT a far cheaper proposition - but there haven't been any technical developments to write home about. This is partly because of the problems with CD piracy on domestic DAT machines. The Sony DTC1000ES, Aiwa XD001 and Technics SV360 machines all either have been, or can be, modified to record digitally on 44.1kHz. Sony have a new system called the Sony Copying Management System (SCMS) which will apparently allow you to copy a CD once and then writes a code to the DAT tape preventing you from making further copies. The politics of the situation are such that Sony have new machines waiting to be distributed but can't make up their minds whether to include the SCMS chip or not. Hopefully, the situation will have been resolved by this summer.

Meanwhile, the sales of DAT machines go from strength to strength. HHB report a sales increase of some 20-25% over the past six months and Ampex, the big guns of audio tape, have seen a substantial rise in DAT tape sales over the past year.

SEMI-PRO USE

WHEN YOU CONSIDER how long it takes the average engineer (pro or otherwise) to be able to get good results recording with analogue tape, it should come as no surprise that making good digital recordings isn't without its own problems. And it also should be pointed out that certain bad habits which yield good results when working with analogue tape machines do not carry across to digital.

Due to the nature of analogue audio tape and recorders, they exhibit certain characteristics that can be used to benefit the music being recorded. The most obvious of these is over-recording. When you push the meters into the red, the first result is tape compression. This is where the dynamics of the music are no longer as clearly defined, and is followed by a gradual harshness creeping into the top end of the signal. This harshness continues to get worse to the point where it's categorised as distortion (though this point will vary from person to person). This initial effect of signal overload is often used creatively. The soft compression often manifests itself as "warmth" although you should never lose sight of the fact that it is still distortion. Ears become rapidly acclimatised to sound and what "feels" wrong one moment may well appear to be pleasing the next. Listening back to the recording the next morning may, however, show you just how unobjective you had become after a lengthy session.

Where digital recording is concerned, meter-pushing is something to be avoided. There is only one way to describe the sound of digital distortion - painful. There's no warmth, no soft edge to the music, just unpleasant distortion. Bad habits once learned can be difficult to break. Monitoring off tape is one habit that helps you keep an eye on your results - unfortunately this is not normally possible with DAT. Apart from the Fostex D20 and the up-and-coming Nakamichi 1000, both of which are very expensive, no DAT machines allow this form of monitoring - which means that you appreciate your mistakes only too late.

The dynamic range of an analogue recording system is frequency dependent; that is to say, the dynamic range will be different for different frequencies - or sounds - in a recording. Again, this is not the case when dealing with a digital recording system. When working with analogue, you become accustomed to pushing lower frequencies in order to achieve satisfactory definition off tape. The corresponding result from a digital system is inverted speaker cones.

Another unpleasant surprise awaits you when you first begin to use a DAT recorder - you'll find out just how noisy some of your trusted equipment actually is. Some synths are exceedingly noisy: Yamaha's TX7 and Roland's MKS70 and U110 exhibit a disappointing level of noise when recorded onto a digital system. The problem arises because, while standard cassette or quarter-inch reel-to-reel machines will play back noise down to around -65dB, DAT is good to at least -90dB (nearer -96dB on more expensive models). Consequently, what was inaudible noise becomes a recognisable problem.

Few samplers allow you to fade out a sample - and this spells trouble when trying to fade a sound which is either inherently noisy or which has too much background hiss. The usual procedure with a bass drum, for example, is to cut the sample close to the end of the sound but to leave a short tail after it. This leaves a bit of hiss on the release of the sample which you will probably have been unaware of until DAT came along. And that noisy slider on your mixing desk will now sound like a fresh crisp packet at point blank range. Untidy drop-ins, too, will have to become a thing of the past if you're serious about "going digital".

If all this is making your dodgy old Revox or tired hi-fi cassette deck sound more friendly by the minute, don't despair. DAT isn't there to make you re-think your entire studio. But it will mean you have to tidy up a lot of the sloppy working practices you've been getting away with. And a few simple rules of thumb will be worth their weight in gold: dropping in and out of record at the same time as a dynamic peak such as a bass drum or snare drum will hide any clunks due to the multitrack transport, and using a noise gate, especially one with a downward expander, will also keep recorded noise to a minimum. Single-ended noise reduction units, such as the Symetrix 511 or the dbx SNR1, are invaluable both for recording onto a multitrack and across the mixer outputs on mixdown, where their program-conscious nature will ensure that background noise is minimal.

Even after taking every precaution possible, there is one area of working with DAT that's very difficult to get around. Because R-DAT recorders are at the kind of price which interests studios using predominantly semi-professional equipment, the inherent noise is a factor which will make its presence felt. For example, if a noise gate is used for autofading, the noise attributable to its circuitry may still be in the region of 30dB worse than that which can be recorded by DAT and will set itself as the reference point for the noise basement. A system will only be as good as the final link in the chain, if that link is being used to reduce the overall noise of the system.

SOUND ADVICE

THROUGH USING DAT frequently over the past year, I've already had to deal with many of the sorts of problems you're about to encounter if you invest in a DAT machine. I'll give you a few examples.

There's never enough room on the DAT cassette inlay card to write down everything you need to - Ampex make a slightly more professional package with one or two tapes in a Betamax-sized case with sheets of A4 printed for song details.

OK, you can write everything down on separate pieces of paper, but that's not quite as convenient. I tend to keep a folder specifically for this purpose.

DAT tapes are similar in construction to analogue cassette but differ in one main respect. If you look at a standard C120 against a C60 compact cassette, you will notice that the amount of tape inside the casing is the same and yet plays for twice as long. This is because the acetate backing is thinner - one very good reason to avoid C120s. Comparing a DAT R60 with an R120 you'll notice that there is substantially more tape in the latter. This is because the actual quality of tape is the same, so you need more tape to get a longer playing time. A two-hour tape costs perhaps 40% more than a one-hour tape.

So how much more expensive is a DAT tape than a compact equivalent? Two decent metal C60s will cost around six pounds while an R120 is around nine pounds. Not as much difference as you may have thought.

We all know what happens when we copy a cassette: the tape hiss builds up (as the square of the number of copies) and the dynamic level decreases with each copy until you're sure that there is something on tape but you're not quite sure what it is. But as DAT encodes the signal into zeros and ones and uses a method to record these onto tape which is particularly stable, it is not prone to the same cumulative deterioration (this is what's at the heart of the DAT copycode controversy). This doesn't mean that making copies of DAT tapes between two machines using the analogue in/outputs will give perfect copies - the signal is being continuously decoded/encoded and so the noise from the pre-amps will then be recorded. However, as we are dealing with a digital signal, it can be copied from one tape to another using the digital inputs and outputs. This will effectively clone the original instead of merely copying it. This is certainly the best way of backing up master DATs.

Finally, a lot has been written about the "drop-out" or audible glitching of DAT. It has been suggested that DAT is not a "professional" medium because of this. But from personal experience, I can say that I've never heard a glitch when using DAT, and this includes cloning a DAT tape over 50 times to see whether any audible difference could be heard. DAT appears to be more reliable than compact cassette if for no other reason than the far superior design of the casing (which is a scaled-down version of a video tape).

DAT OR NOT?

DAT IS A technology which is unlikely to take off in a domestic sense - for which it was initially marketed - and as the demand is low the prices are unlikely to fall much further than they already have. But even Casio's modest DA2 recorder will out-perform practically any cassette deck or two-track reel-to-reel machine. Does DAT, with its unpleasant distortion characteristics produce an "uncomfortable" sound? Personally, I think it sounds smoother than many CDs I've heard.

If you're considering adopting the new DAT technology as the mastering stage of your studio - whether it's a pro, semi-pro or even "personal" setup, it offers a far higher quality medium than any of the alternatives. There are machines available to suit deep and shallow pockets alike and the portability of some of the machines also makes them perfect for "field recordings" to be transferred to a sampler later. Give this technology a close look over. I think you'll be impressed.

For those of you interested in moving into DAT, we've compiled a list of most of the DAT machines currently available in the UK. Please note that specifications are not intended to be exhaustive, and if you have an interest in a particular machine, you should contact the relevant distributor for full Information.

AIWA HDX1

Probably the smallest, and one of the cheapest DAT machines currently available, the HDX1 is almost pocket-sized, making it eminently portable. New 1-bit oversampling converters give good audio performance and its low selling price makes it a sensible first machine or backup choice. A remote control is supplied and the machine offers digital Ins and Outs.

CASIO DA2

The DA2 is a compact, portable, budget DAT recorder with 15-bit sample resolution, featuring a rechargeable battery pack for mobile recording. Special functions include the ability to program start IDs automatically or manually for display at the beginning of a selection, the ability to edit or delete IDs during playback and a Skip Play function to allow you to skip selections in forward or reverse. No digital In/Out is provided.

CASIO DA1

The predecessor to the DA2 is still available on the secondhand market.

FOSTEX D20

The first production digital recorder from Fostex, the D20 is an impressive machine with professional facilities and a price to match. One of its main applications is intended to be as a stereo mastering machine offering full SMPTE facilities, as it replicates the timecode and control capabilities of quarter-inch analogue timecode machines and also offers a range of familiar features. Despite the D20's SMPTE features, tapes recorded on it are fully compatible with all existing DAT machines on the market. Numerous features on offer include glitch-free varispeed, punch in/out editing and timecode refresh. An optional 8320 remote control is also available.

TASCAM DA30

A professional-quality DAT recorder with a range of features including XLR balanced analogue inputs and outputs, AES/EBU digital interface and 8-times oversampling 18-bit D/A conversion, plus a range of start and skip ID editing functions and a comprehensive display panel which includes a Margin display (shows available headroom in dB). A wired remote control unit is supplied with the DA30.

TECHNICS SV360

This is a professional quality, 2U-high rack-mounting unit. During recording, the SV360 uses two A/D convertors with 18-bit resolution to reduce conversion error by 75%. Features offered include an indexing function which allows you to add and delete skip ID and start ID markers even after recording, multiple sample frequencies, balanced XLR analogue In/Out and coaxial digital In/Out, plus a supplied remote control unit.

TECHNICS SV260A

A compact, professional-quality DAT recorder whose small size is achieved by a unique, half-size head drum. Features include S/PDIF digital output (no input), End Search function providing instant access to the end of the recorded material on the tape, and high resolution meters. The 260A differs from the previous 260 in that it has an improved microphone input.

SONY DTC1000ES

Professional quality, rack-mountable DAT recorder which has become the studio standard machine. Digital Ins and Outs are to the S/PDIF format, and the machine has its own infra-red remote control. Features offered include start ID and skip ID, and a full array of sub-code indexing routines.

SONY PCM2500

The PCM2500 is based on the DTC1000ES, but features a wide range of additional facilities which suit it for both broadcast and studio recording applications. These include balanced XLR connectors and analogue ins and outs. It accepts SDIF 2 and AES/EBU digital inputs at 44.1kHz, and S/PDIF at 48kHz to allow transfer to and from other DAT recorders. Supplied with both infra-red and wired remote, and can be rack-mounted.

SONY PCM 2000

A portable recorder designed especially for ENG (Electronic News Gathering) applications. Its principal feature is a linear track time-code capability. Other features include rugged design and long record time.

SONY TCD D10

A portable DAT recorder weighing only 1.8kg, the TCD D10 is supplied with a comprehensive range of accessories including carrying case, power unit, batteries and recharger, remote control and stereo microphone. No digital In/Out.

SONY TCD D10 PRO

This portable recorder is an upgraded version of the TCD D10, featuring professional features and functions, including balanced analogue line level inputs with XLR connectors and digital In/Outs in both AES/EBU and S/PDIF formats. It records from analogue input at 48kHz and at 48kHz, 44.1kHz and 32kHz frequencies from a digital input. Improvements over the TCD D10 include new design high resolution LCD offering 20-segment peak-level metering.