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Alesis ADAT XT

8-track Digital Audio Recorder By Paul White
Published January 1996

Alesis ADAT XT front panel.

ADAT is dead, long live the ADAT XT. Paul White reports on the rebirth of a classic.

When Alesis first introduced ADAT to a sceptical world, nobody was quite sure whether an 8‑track recorder based on a souped‑up domestic video transport would last the course, but history bears witness to its staying power. Inevitably there were teething problems, but ADAT has become an accepted and respected part of the audio community, both in amateur and professional circles, with a good many hit records to its credit.

The operating software and the transport have both been revised since the machine was first launched, and ADATs have proven themselves to be tough little workhorses, with some owners apparently reporting up to 10,000 hours of use from a single machine (at today's ADAT prices, this works out at little more than 25p per hour running costs!). However, by the time you read this, the familiar ADAT will have been out of production for almost three months and supplies of discounted, end‑of‑line stock will be dwindling.

What's New?

Alesis have kept very quiet about ADAT's successor, the ADAT XT machine, and although I got wind of it around a year ago, I was sworn to secrecy. Obviously they didn't want to fall into the old trap of announcing a product before they were in a position to deliver it. As is evident from our photograph, the XT is quite different from the original ADAT, and the difference is even more apparent when you see one close up. The brushed and sculpted aluminium front panel looks like a block of stainless steel, while the custom plasma metering system wouldn't be out of place on a top‑flight DAT machine. Many of the features previously accessible only via a BRC (Big Remote Control) are now directly served from dedicated front panel buttons, and all the controls have been designed to look and feel very professional and 'expensive'. Unfortunately, certain of the button legends are a little difficult to read in subdued lighting conditions, especially Format and Edit Value which are printed in dark colours on a dark background. Pity.

To touch the XT is to want to possess it, and I've already bolted the two review models into my rack and filed the heads off the mounting screws!

Inside the casing, new ASICs (Application Specific Integrated Circuits) have taken over completely from LSI (Large Scale Integration) chips, and the whole mechanism is now supported on a rigid, cast aluminium chassis, making the XT machine rather heavier than its ancestor. I'm told the chassis alone weighs seven pounds.

Another change is evident in the converter section of the machine where new 18‑bit, 128 times oversampling A/Ds and 20‑bit, 8 times oversampling D/As produce a very healthy signal‑to‑noise ratio in excess of 92dB and a 20Hz to 20kHz frequency response flat within half a dB. The optical ADAT interface and sync cable setup is exactly as it was on the original machine, allowing up to 16 recorders to be locked up to provide a 128‑track system.

Paradoxically, where the greatest change is evident is the area that has changed least in hardware terms — the transport. If you've heard anything at all about the ADAT XT, it's probably that the transport winds significantly faster than it did on previous ADATs, but at heart it is based on the same Panasonic SVHS mechanism. Essentially, the transport has been modified so that it is capable of winding around four times faster than before. But unlike the previous model, where you had to disengage the tape from the head to achieve a good fast‑wind speed, the XT keeps the tape engaged at all times in normal operation (unless the machine is left idle for several minutes, in which case the tape unlaces itself to prevent head wear). It is now possible to go into disengaged mode by hitting Stop twice to double the fast‑wind speed, but this is unlikely to be needed unless you're completely rewinding a tape. The outcome is that the fast‑wind time is about 40 times play speed which, although not quite as nippy as a DAT, is actually quite close.

Though I have no in‑depth details, I understand that a radically new set of control software has been developed for the XT which provides dynamic braking. In order to keep the tape handling as fast as possible, the system constantly monitors the machine's winding performance and 'relearns' the transport characteristics continually, allowing it to compensate for overshooting when fast‑winding and so on.

Keeping the tape threaded ensures faster lockup, because the machine can read its own timecode during fast‑wind, so that it always knows where it is. Head wear is said to be negligible, because a protective cushion of air now forms between the tape and the head in fast‑wind mode. In fact, on talking to Alesis' UK distributor Sound Technology, they inform me that in all the time ADAT has been on the market, they've never yet come across a single head that's been worn out. They've had to replace damaged heads from time to time, but never worn‑out ones.

Other external differences become evident when you look how the XT connects to the outside world. EDAC connectors are still used to provide professional (+4dBu) balanced connections, but the ‑10dBV ins and outs now use phono connectors. Jacks are still used for the Punch In/Out and Locate/Play footswitches, and a newly designed LRC (Little Remote Control) now provides access to the auto punch‑in/out functions of the machine as well as to the more basic transport functions.

Is It Compatible?

Current ADAT users are going to want to know if the ADAT XT is compatible with their existing ADATs, and the answer is 'yes' — but with certain stipulations. Firstly, if a BRC is being used to control the system, it should be fitted with no lower than software version 2.03 and preferably version 2.04, otherwise it won't work properly. Secondly, the XT should be the master or first machine in the system, because of its faster transport. The chase and lockup time will still be dictated by the slowest machine in the system, so for real improved performance in this respect, you need to use only XT machines.

There is one more point to watch, and this is something I've only become aware of recently. Apparently, the original ADAT inverted the phase of the input before digitising it, and then reinverted the phase after conversion back to an analogue signal. This is fine, since no phase inversion occurs from analogue input to analogue output, but the new XT has been rationalised to eliminate the phase inversion of the digital data, because some users were transferring their digital data to hard disk and then wondering why it was inverted in phase. This being the case, there's no problem mixing ADATs in a system, but if you take a tape made on an old ADAT and play it back on a new XT (or vice versa), the phase of the audio output will be inverted. In most situations, this won't cause a problem, but if you have a multi‑microphone setup or a stereo pair split between two machines, then you could come unstuck. Once you are aware of the problem, of course, you can compensate by using the phase invert buttons on your mixing desk.

One feature I had hoped to see on the XT is a basic MTC (MIDI Time Code) output. Sadly, there isn't one. Even a simple system with 25 or 30fps selection and no offset control would have been useful, as most users can take care of offsets inside their sequencer packages. As it is, you still have to buy an external third‑party box (available from J.L Cooper and others) or a BRC.

Front Panel Access

Before continuing, I'd like to cover the functions that are now accessible directly from the front panel. Previously, pretty much all of these could only be used if you had a BRC, though there's one important addition in the form of a switchable 44.1/48kHz sampling rate. This doesn't make any difference to the audio quality, but for anyone mastering onto two tracks of the XT who then wants to clone onto DAT or a hard disk editor (via something like an AI‑1 interface), it saves having to pass through a stage of sample rate conversion. However, when the machines are under the control of a BRC, the BRC provides the master clock, and at the moment this is set to 48kHz only (unless you cheat using the varispeed), so perhaps a BRC software update is in order?

The XT is a natural and worthy evolution from the phenomenally successful ADAT...

The metering can be directly switched from absolute to relative mode, much as it can on the BRC, and tracks can now be copied from one to the other in the digital domain. The punch‑in crossfade time can be selected from 11 to 46 milliseconds. In systems of two or more machines, an offset can be added to allow a chorus from one machine, say, to be pasted to several different locations on the other machine. Such offset copying obviously isn't possible with only a single XT.

The display helps when setting up offsets — a miniature bargraph display shows you the amount of track delay you've entered. Individual tracks may be delayed by up to 170ms to compensate for timing errors, or simply to create effects, and very usefully, the front panel now includes a full 10‑point autolocator accurate to 10ms — the same resolution as the tape counter. Another first is the ability to drop individual tracks in and out of record using the Record‑Ready buttons — with the revered ADAT, you had to first select your tracks with the Record‑Ready buttons, then place them in and out of record all at once.

The display now has three rather useful peak display modes (no hold, short hold, hold peak until cleared) and plenty of status information is available in the window; dedicated, illuminated legends are now used for specific functions instead of the more cryptic display of the older ADAT. For example, when formatting, the word 'Format' is illuminated and the current sample rate is always shown; when two or more machines are establishing lock, the word 'Chase' is displayed followed by 'Locked'. Far nicer...

The original ADAT offered only two autolocate points plus a return‑to‑zero function, but the XT features a full 10‑point autolocator which is quite independent of the BRC and, to my mind, rather more logical to operate. BRC users can, therefore, enjoy the luxury of 10 additional locate points with the proviso that the XT's own locate points can only be accessed from the XT's front panel, not from the BRC. Exactly the same is true of the auto punch‑in/out function — if auto punch‑in is executed from the BRC, then the XT's own auto punch‑in function isn't used, but if an auto punch‑in is executed from the XT's front panel (which works between autolocate points 2 and 3), the BRC doesn't get involved at all, other than as a remote transport control.

There's also a loop function that allows the section between locators 1 and 4 to be repeated indefinitely, with the option to work in loop record mode so that you can keep cycling over a section until you get it just right. Occasionally, you can get caught out by not turning off the track copy or loop functions when you've finished with them, but at least the information is shown in the display if you look for it.

Sadly, the meter outputs fitted to the earlier ADAT have not been carried through to this model, so anyone with an RMB meter bridge (apparently only me, according to the sales figures!) will be left with an expensive paperweight when they upgrade.

In Performance

I managed to verify that the front panel functions worked OK with very little effort, thanks to a very clearly written manual. The biggest difference is in the transport speed, but the best lockup time is also slightly improved, clocking in at around 2.5 seconds. However, the transports of multiple machines seem to keep much better pace with each other during enganged fast‑wind, so the whole lockup procedure is much more consistent with few legitimate manoeuvres taking more than three seconds. If you try to drop into play directly from fast‑wind, however, the system hunts for a while, taking up to seven seconds to lock if you've just done a very long wind. On the other hand, if you've just spun back a few bars to perform a drop‑in, the lockup time can be almost as quick as if you had used the locators. Even so, the rule remains the same as it was with the original ADAT — let the machine park before you hit Play, or use the locator points if you want the fastest possible lockup times.

Where the new XT system definitely scores is that it is far less prone to hunting aimlessly if you try to lock up when the two transports are fast‑winding at different time locations. The way in which the transport gets the second machine into the right position seems much improved, even when you deliberately offset the two machines — so perhaps this intelligent 'learning' transport software really is a bit clever.

Tape handling seems smoother than before, with less clunking and more whirring, no doubt again a result of the new control software. Due to the incessant demand for longer recording times, it's now possible to select 180, 240 or 260 minute (PAL) tapes, giving from 40 minutes to a maximum of 62 minutes recording time. The use of 180 or 240 tapes was possible on the older machine, and once again the function is selected using an odd combination of existing buttons. It's also possible to use the shorter 60 minute tapes on an XT, though there's no need to tell the machine because it can recognise these tapes from their shell casing. The same length of tape should be used in all machines, and if the XT is being used with a BRC, the tape length setting will be memorised when the system is turned off. As expected, the first two minutes of the tape is reserved for header data, which includes the BRC setup and song data. Unlike the Fostex RD8 ADAT, however, there seems to be no way to save a setup of the XT's own locator values onto the tape.

Despite the increased number and smaller size of the control buttons, the fact that there are relatively few 'hidden' functions makes XT operation extremely simple. One hidden function that I did find informative was the error readout. In normal mode, you get a simple blinking red indicator if a serious error occurs, but by selecting the Error Rate display (Set Locate and Rec Enable 3), a continuously updated error rate is shown after the tape counter display figure. This will always show a few errors in normal usage and counts the errors per 14 drum revolutions before resetting. Readings of less than 10 are considered fine and new tapes will apparently read up to 100 errors with no problem. Rates above 1000 are corrected by interpolation — which means the machine is actually making up data to fill the gaps. So if you get error readings much over a couple of hundred, I'd recommend cloning the tape as quickly as possible. On a new 3M ADAT tape, I got typical error rates of between 2 and 7, which I feel happy about.

It delivers better performance, more features, and much nicer styling for just a little less than the original price of ADAT.

So what about the sound quality? The new converters are technically superior to the original ones, and on some material it is possible to hear a difference, though it is very, very slight. If anything, the sound is smoother and less metallic than it used to be, but then I never had any argument with the sound quality of the original ADAT.

Summary

The Alesis ADAT XT certainly looks a lot nicer than its ancestor and the rigid chassis gives it a reassuring feel, but I'm still a little irritated by the lack of any meter sockets and I know that some users will frown at the inclusion of phono sockets. Personally, I think phonos are fine if you're not going to keep unplugging them, and if you want to run balanced, there's always the EDAC connector. The faster wind speed is much welcomed, as is the apparently gentler tape handling. Although the best lockup time is still around 2 to 2.5 seconds from a standing start, the lockup procedure does seem far more consistent with no unexpected long waits.

Front panel access to the previously hidden features is a great bonus to non‑BRC users, but anyone using BRCs has little to gain in this area (other than the admittedly useful ability to drop individual tracks in and out of record, and of course the better error rate readout). There's also little to be gained on the speed front if you are mixing ADATs with ADAT XTs in a multi‑machine setup, because the slower machines will always dictate the maximum search rate. On the plus side, just one XT working as a master does provide access to all those hidden functions without the need for a BRC. In fact, the only real let‑down is the lack of an MTC output, a disappointment that I know a lot of people will share.

All things considered, the XT is a natural and worthy evolution from the phenomenally successful ADAT and is pitched at the same markets. It delivers better performance, more features, and much nicer styling for just a little less than the original price of ADAT, and once you've played with one, I think you'll like it as much as I did. Alesis have made their mark on audio history with the ADAT format, and have confirmed their commitment to the ADAT project by continually refining and updating the software. I'm sure that the new XT will enjoy similar support, which leads me to speculate on the possibility of a shiny, silver BRC II, an add‑on MTC box, and possibly a periscope attachment for those of us who want to the read the meters when the XT's are whirring away under a table or round a corner? Regardless of what the mobile phone people say, it looks as though the future is silver. To touch the XT is to want to possess it, and I've already bolted the two review models into my rack and filed the heads off the mounting screws!

Pros

  • Much faster winding speed, better tape handling and more consistent lockup times.
  • Previously 'hidden' features can now be used directly from the front panel controls.
  • Heavier construction and infinitely nicer styling.

Cons

  • Still no MTC output.
  • No meter outputs for the (now discontinued) Remote Meter Bridge.
  • I refuse to whinge about the phono sockets!

Summary

A very elegant, second generation ADAT which offers most benefits to non‑BRC users. However, the more professional presentation and faster tape handling will appeal to all users. Another classic.

Published January 1996