Alesis XT Digital Reverb
For even less than the price of a semi in Rotherham, you too can experience high quality digital reverb in the privacy of your own home.
Whenever a new product hits the market, the words 'price breakthrough' and 'revolutionary' are bandied about all too frequently, but if applied to the Alesis XT, there would be some justification.
You can now get a truly flexible and high quality stereo digital reverb that will give you change from £1000 - though you might only just be able to afford fish and chips on the way home.
Hailing from Los Angeles, California, the Alesis offers fully variable decay times between 200ms and 10 seconds, and eight switchable parameters allow the creation of a great number of different reverb effects. You can probably tell from the photograph that this is a 1U device of standard 19 inch width and 9¼ inch depth so I won't even mention these facts - so now on to the interesting bits.
With the exception of the defeat switch socket, all the controls are mounted on the black anodised front panel and as you might expect, the first one that you're likely to need is the input level control which works in conjunction with a six section LED ladder meter. The Mix and Output controls are fairly self explanatory, as is the Decay control which gives a maximum reverberation time of around ten seconds in a fully clockwise position.
Of course there is much more to simulating a specific reverb effect than simply altering the decay time; both the pattern of the initial reflections and the spectral content and density of all subsequent reflections play a vital role in giving an acoustic environment its identity. The simplest parameter to introduce is pre-delay, which creates an illusion of space by delaying the onset of the initial reflections for a finite time after the initiation of the original sound. The Alesis XT has a switchable pre-delay, the exact value of which depends on the setting of the Size control. This latter function gives a choice of two reverb algorithms, one for small rooms and one for large halls. The main difference between these settings is that a small room exhibits more pronounced resonances than a larger room, and as such generates a more coloured sound.
Slap Back is, as far as I know, unique to the Alesis XT - certainly at the budget end of the market and is an extra stage of pre-delay with feedback. This extends the duration and complexity of the reverb pattern and gives a bigger sound, though it does create a hint of a flutter at longer decay times.
In order to further extend the range of effects that can be produced, two rates of diffusion are selectable. With the button depressed, there are more reflections in any given period of time lending a smoother texture to the reverb decay. This is a particularly useful option for use with percussive sounds as the least diffuse setting can sound granular, particularly on low toms or bass drums.
The spectral content of the reverb can be modified by switching in a high-cut or a low-cut filter to emulate, the reflective qualities of various surfaces whilst the HF Damp option causes the high frequency component of the reverb tail to die away faster than the low and middle frequencies, thereby simulating the absorption characteristics of a typical room or hall.
Lastly comes the defeat button, which like all the other buttons has a status LED, and this cuts off the input to the reverb circuitry, allowing any sound already reverberating to die away naturally rather than be cut off abruptly. This function may also be controlled via an optional footswitch which is connected to a standard jack socket on the rear panel.
On the rear panel itself, the mono input and twin stereo outputs are quarter inch unbalanced jacks and an extra pair of sockets are wired as an effects loop after the input level control but before the level meter circuit. Extra delay or other signal processing equipment may be patched in at this point, though for most applications, nothing extra would be necessary.
With a frequency response extending from 30Hz to 14kHz, the XT in this respect equals or even excels most upmarket models. A dynamic range of 75dB ensures low noise operation and the unit will cope with a wide range of signal levels giving adequate headroom, even with a system operating at +4dBm levels.
Technical specifications are important in so far as a unit should perform quietly and without significant distortion, but with something as subjective as reverberation, the only viable way to evaluate the effect is to use your ears.
Units such as the Lexicon PCM60 offer a choice of plate and room programs but with the Alesis XT, the user has to create the desired sound by combining the push button parameters with a variable decay time. This is quite satisfactory in most cases and if the user keeps a record of useful settings, these may be quickly and accurately set up at a later date.
The basic reverb sound lies somewhere between a room and a plate but by combining the in-board parameters with a little external EQ, both types of effect may be convincingly reproduced. In fact, the only currently popular reverb sounds that can't be set up are the so-called non-linear and reverse programs which are not really to be expected at this price. Having said that, the unit is software updateable and so future updates may well include these effects. It is however possible to use a noise gate in conjunction with the Alesis XT to create the popular gated drum sound, and a short reverb with pre-delay also sounds quite convincing if you don't have a couple of spare gates.
In practice the reverb was smooth and fairly natural in character with plenty of stereo depth though with all the filters out, the reverb sound can be made much brighter than anything normally encountered in real life. Used with drums, the setting with maximum diffusion gave the smoothest sound but the bass drum tended to sound rather crunchy when large amounts of reverb were applied. This is not a criticism of the Alesis but more an observation of a side effect which is evident on nearly all digital reverbs, even the very expensive ones, and is probably due to the extended frequency response of digital reverb processors.
It is however unusual to add any significant amount of reverb to bass drums, so this is not really a problem and the overall impression is one of quality and sophistication beyond what would normally be expected of a unit in this price range. Background noise was minimal.
Vocals and instruments were also handled with ease and the resulting sound was natural and bright without any bad habits or side effects being evident.
The inclusion of a pre-delay is a real boon because you don't need to tie up your main DDL in such trivial pursuits and it adds terrific depth to percussive and vocal sounds. I found that the extra slapback facility was a little over-the-top for most purposes but as it's there, I'm sure that it will find its uses for thickening vocals and so on.
Criticisms of the Alesis are minor, even when its surprisingly modest price tag isn't taken into account. True, there is no power-on mute so if your studio is isolated by a single contact breaker as mine is, the initial burst of noise is fed directly to the monitor system, and this can be a source of alarm for the studio cat.
The basic performance however, both in terms of subjective appraisal and lack of unwanted noise is really very good and I would venture to suggest that very few people could tell if a mix were done using this unit or a top industrial model, provided that the effects set up were similar and the reverb not over prominent in the mix.
That isn't to suggest that the Alesis is as good as an AMS or a Klark-Technic unit because after all, it's not programmable, much less flexible, and you can tell the difference if you compare the reverb only sound. It does, however, show that the budget units are catching up with the big boys and the law of diminishing returns is as applicable now as it ever was.
Further information is available from Atlantex Music Ltd, (Contact Details).
Review by Paul White
mu:zines is the result of thousands of hours of effort, and will require many thousands more going forward to reach our goals of getting all this content online.
If you value this resource, you can support this project - it really helps!