David Mellor compares the new Sony DTC M100 Digital Audio Tape recorder with the studio industry standard - the Sony DTC 1000ES.

DAT IS...

DAT - he says, desperately trying to avoid puns on the word 'that' - is a cassette-based digital recording system. It uses a 16-bit data format (like Compact Disc) and a sampling rate of 32, 44.1 or 48kHz (Compact Disc is always 44.1 kHz). I should add that there is provision in the DAT format for 12-bit operation, but I know of no machines that can record to that standard.

Why there should be a multiplicity of sampling rates is a good question: 32kHz is there for recording audio directly from digitally encoded satellite broadcasts, with the appropriate receiver; 48kHz is there as the standard DAT sampling rate. Recording at 44.1 kHz is supported only on professional DAT machines like the Sony PCM 2500 or Fostex D20, although all machines can play back at this sampling rate. Digital copying of 44.1 kHz recordings is not allowed on 'domestic' machines like the 1000ES and M100, to prevent you from making digital clones of Compact Discs. You can thank the record industry for that restriction.

Of course, there is no restriction on what you can record through the analogue inputs of any DAT machine. And since CDs copied onto DAT this way sound hardly any different if you are listening on home hifi, and an infinite number of 48kHz clones can be made from one via-analogue copy, the 44.1 kHz restriction has hardly achieved anything, has it? That's politics for you, and the music industry has managed to all but kill off DAT as a domestic recording medium.

For the creative home recordist, it would be a problem not being able to record at 44.1 kHz. If you are aiming to release a CD of your music, then your 48kHz DAT recordings will have to be 'sample rate converted', losing a dB or two of signal-to-noise ratio in the process, or - more likely - converted by passing through an analogue stage. Either route is inelegant and less than optimum.

Thankfully, although the standard off-the-shelf DTC 1000ES is not able to record at 44.1 kHz, the machine is available with a small modification which makes the pro standard sampling rate possible. Unfortunately, the word is that second generation DAT machines like the M100 have been constructed as 44.1 kHz-free zones from the ground up. There is apparently no modification, simple or otherwise, possible which will enable 44.1 kHz recordings to be made. Or is there an electronics boffin out there who knows different? We'll have to wait and see.

DTC M100

Just because the DTC M100 can't record at the CD sampling rate doesn't mean that it has no potential for the home recordist, just that it has a slight limitation when it comes to using it as a mastering medium for later CD release. (Students of the English language may care to spot the triple negative in the last sentence!).

The sound quality of DAT, even domestic DAT, is extremely good. In fact, to obtain a similar standard of sound quality on analogue equipment would cost at least four or five thousand pounds for a decent stereo tape recorder and noise reduction unit. I have compared the sound quality of my 1000ES with the M100, and also the M100 line in and line out, and I can't detect any significant difference. Full marks for that.

In presentation, the M100 is definitely not a pro engineer's tool - but neither is the 1000ES. I saw a modified version of the 1000ES, at a recent exhibition, which was intended to be used in radio stations. It had an extra box fastened onto the bottom with lovely big buttons - Red for Stop and Green for Play, and such like. Fiddly little hifi buttons are not conducive to efficient operation. The Stop and Play buttons are the right size, if not the right colour, but the rest are just too small.

But does the M100 have the right buttons for the ambitious home recordist? Let's see...

The DAT format includes data recording as well as audio. This data includes Start ID codes, which not only identify the beginning of each track but also number them. When I first encountered this facility on the 1000ES, I was a little sceptical of its value. But that was because I wasn't used to the particular requirements of the cassette medium.

The Start ID codes perform the same function as white leader between tracks in reel-to-reel tape, and the machine can be programmed to play from any ID number. There are also Skip ID codes, which you can use to automatically pass over any passages which you don't need to listen to.

As well as the transport controls, ID code related controls, and the essential recording level control, the M100 has a numeric keypad used for finding the particular track you want to listen to. There can be up to 99 numbered tracks on a DAT cassette, which is sufficient for most purposes (but not all, according to at least one engineer who archives samples onto DAT). Actually, you can repeat the codes 1 to 99 as many times as you like, but it makes finding the right track tricky, so it's best to stick to what the machine can properly understand.

There are enough controls to keep most people happy, but one function that I would have liked, however, is some sort of autolocation that did not rely on codes recorded onto the tape. But the M100 is a domestic, not a studio, machine and autolocate functions were probably not considered appropriate.

Metering is via a fluorescent bargraph display. With my DTC 1000ES I find that the meter is not quite fast enough to register some signal peaks. The red 'Over' LED, which lights when you try to put too much level into the system, is faster than the bargraph itself but I have still been able to find material which meters OK but causes slight clipping. The meter and peak LED on the M100 both react, as far as I can tell, with the same speed. There is a small margin for error above the level at which the peak LED comes on. I tried to catch it out with some peaky synth waveforms - but this model was not to be fooled.

There is an extremely useful extra feature on the M100 that I have been wishing for for years - a display of the maximum level achieved during a recording, called 'Margin'. With a display such as this, you don't have to keep your eye on the meters all the time to check that a recording has remained within bounds throughout. For example, if the highest level during a recording, so far, has been 5.5dB below absolute maximum, then the Margin display will read -5.5dB and hold that value until a higher peak comes along or until you press 'Margin Reset' to start the process over again.

Of course, you and I should be closely monitoring our recordings as we make them, but it's good to have a second opinion.

DIGITAL COPYING

Having DAT is nice, but if you only have one machine then you soon realise the limitations of the cassette format (as outlined in a separate panel). A second machine for copying would seem ideal, but with the DTC 1000ES/M100 combination, there are certain problems.

The 1000ES has two phono sockets for digital input and output (each phono carries both left and right channels). The first thing I noticed when I tried to hook up a digital link to the M100 was that HHB's otherwise perfect 19" rack-mounting tray for the 1000ES has a metal bar right in front of the digital output socket. "!", was all I could find to say to that, but I unscrewed the shell of the phono connector and squeezed the rest of it past.

The second point that came to my attention was that the M100 has a digital phono connector, but just for the input. Digital output is only available on a fancy fibre optic output. Now fibre optics may be the latest and greatest thing in interconnection, but not to be able to have two-way digital communication between two Sony machines whose model numbers have the same DTC prefix is just silly.

I'm not one to be beaten and it didn't take half a second for it to occur to me that all I had to do was dedicate my 1000ES to the playback side of the arrangement and the M100 to the recording. But the M100 will not record at 44.1 kHz. It plays back at that rate, but refuses to record. So I had no way of making digital copies of any of my material recorded at 44.1 kHz - which is most of it. I had to conclude that the M100 was not useful in my personal situation. But if you need digital dubs only at 48kHz, then it's all systems go.

PROBLEMS

Unfortunately, digital dubbing problems were not my only source of concern while I had the M100. I have heard talk in the industry that there are occasional compatibility problems when replaying a DAT cassette recorded on a different machine. This was the case with the particular 1000ES and M100 units that I had.

I found that recordings made on my 1000ES machine would not play reliably on the M100; there would be frequent dropouts. Recordings made on the M100 would play fine on the 1000ES. The only conclusion I can come to from this information is that one of the machines is not operating correctly - but which one?

The M100 also had trouble finding Start ID codes. It would record them, and when I transferred the cassette to the 1000ES, that machine could find them, but the M100 could not find its own Start IDs. I am forced to believe, therefore, that the review model was not operating correctly. (I had a similar but not identical problem with the DTC 1000ES when I first used it. It was changed for another unit which has operated absolutely perfectly ever since).

It is never pleasant having to criticise a piece of musical or audio equipment. I always get the feeling that one day a design engineer will come up to me and say: 'Well, let's see you do any better'. But the fact is that if equipment is not suitable for the job in hand, then it should remain on the dealer's shelf.

Assuming that the ID code recording and compatibility problems I encountered are not typical - and Sony does have a reputation for producing quality products - I can come to some conclusions:

Buy the M100 if:
- You want a good digital cassette deck for your hifi.
- You need to check at home DAT cassettes recorded in the studio.
- You want a second DAT machine to make digital copies at 48kHz.

Don't buy the M100 if:
- You need full studio standard functions. (You need the Sony PCM 2500).
- You need to record at 44.1 kHz.
- You need to make digital copies at 44.1 kHz.

To conclude, the DTC M100 would make an excellent alternative to a high end analogue cassette deck, but for general studio use the DTC 1000ES - at a higher price - is the one to go for.

FURTHER INFORMATION

£899.30 inc VAT.

Axis Audio Systems, (Contact Details).