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Alesis Q20

Stereo Multi-effects Unit By Paul White
Published December 1998

Alesis Q20

Paul White meets the latest version of Alesis' Quadraverb concept, and finds it resplendent with 20‑bit I/O, improved digital and analogue interfacing, and a proper internal PSU.

The original Alesis Quadraverb is, I'm told, one of the best selling multi‑effects units of all time. The Quadraverb 2 or Q2 fared less well, however, possibly because it was viewed by many as being simply a revised Quadraverb at a much higher price. With hindsight, perhaps Alesis should have picked a different name, because the Q2 was a totally different device from the Quadraverb — even the 'Quadra' tag was misleading, because it allowed up to eight effects to be used in combination. Though it was still essentially a 16‑bit device, the Q2 was much quieter and cleaner‑sounding than the Quadraverb, and featured an elegant graphical interface that showed exactly how the various effect blocks were connected up. It also had an ADAT digital interface, which was unusual at the time.

The new Q20 is essentially a Q2 fitted with 20‑bit converters, but it's also been improved in other areas, not least in having twice as many user memories. Gone is the annoying external power supply, and in addition to the ADAT interface, there's also S/PDIF in and out on standard phonos. The input sockets are now combi XLRs that can accept balanced XLRs or regular quarter‑inch balanced/unbalanced jacks, and the outputs are available on separate balanced XLRs or balanced jacks. There's also a 48kHz clock input, footswitch jacks for bypass and patch advance, and MIDI sockets for In and Out/Thru.

The new Q20 is essentially a Q2 fitted with 20‑bit converters, but it's also been improved in other areas, not least in having twice as many user memories.

The effects are generated by the same proprietary 24‑bit Alesis DSP chip as was used in the Q2 which, depending on the complexity of the effects chosen, can generate up to eight programmable effects blocks at once, though in most cases, only four or five typical effects can be combined before the DSP limit is reached. You can even use all the DSP power on one super reverb. I think it's fair to say that the high quality of the Q2's reverb went sadly unnoticed, and in its new 20‑bit format, the Q20 reverb is even cleaner and smoother.

Set The Controls

The Q20 features a much greater range of analogue and digital I/O options than its predecessors. S/PDIF joins the digital ADAT connection of the Q2, and the analogue ins and outs are available on either XLRs or jacks.The Q20 features a much greater range of analogue and digital I/O options than its predecessors. S/PDIF joins the digital ADAT connection of the Q2, and the analogue ins and outs are available on either XLRs or jacks.

The operating system of the Q20 is virtually identical to that of its predecessor, but for the benefit of those unfamiliar with the Q2, I'll quickly go over the basics. Housed in the familiar 1U case, the Q20 has a custom display, rotary controls for input and output levels, and a data wheel for patch selection or parameter changing. A dual bargraph meter shows the input level. Cursor style rocker buttons are used for Block and Page selection with just 12 other single function buttons handling the rest of the navigation, and pressing the data wheel acts as an 'Enter' function. Operation really is so simple that most people could find their way around it fairly quickly without ever opening the manual, though because of the detailed display, it helps to have the unit where you can see it clearly. It's also a good idea to read the manual through at least once as there are features that you may never suspect exist from simply looking at the front panel.

The effects occupying the blocks are divided into EQ, Pitch, Delay and Reverb, and further subdivided into over 50 effects type algorithms including hall, room and plate reverb, graphic and parametric EQ, flanging, chorus, pitch‑shifting, delay, rotary speaker simulation, overdrive, Doppler autopanning and even stereo sampling. Blocks may be connected in any order, and the linking between blocks is shown by virtual patch cords in the display window. Each block has stereo outputs as well as a mono mix output and at nodes where signals are combined, the mix ratio can be set by the user. Routing is actually very simple as once you've selected a signal destination, you simply use the entry dial to scroll through the available sources and then pick the one you want. The display graphics change dynamically to follow this process so you can always see what you've got.

Creating or editing a patch involves selecting one of the blocks, then using the panel buttons to select Type, Routing, Parameter or Mix. The Block cursor buttons are used to move from one block to the next, and blocks may be added or removed at will up to the maximum the DSP can support. A new Quick Route feature has been added that allows any block to receive signal direct from the left and right inputs (separately, from either one or mixed) and to have its outputs sent directly to the left and right outputs. The wheel scrolls between None, Left, Right or Both. Routing levels can be changed to prevent overload caused by EQ boost and so on, and in Quick Route mode, the routes added are set to ‑6dB until changed by the user.

As well as the basic effects, the Q20 also includes two modulation source generators, each of which can be set to Input Envelope, Peak Follower, Ramp, LFO or Footswitch. Real‑time MIDI modulation of up to eight parameters per patch is also possible, though the parameters that can be controlled depend on what effect type is assigned to a block. Again, setting up is simple: select a modulator, choose a target, choose the modulation source and set the amount of modulation.

In Use

I've used a Q2 before, so the Q20 felt quite familiar to me, but even if you're a little nervous of effect programming, there are so many good presets that most of the time you can tweak one of these to give you what you need within a few seconds. There are 100 factory presets plus 200 user memories, which come ready filled with interesting patches for you to use, edit or replace. Most of the factory patches are identical to those in the Q2, though there are a few new ones. The reverbs are exceptionally smooth and luxurious‑sounding and the overall range of effects is pretty comprehensive, though occasionally you find them lurking in odd categories. For example, the EQ section also includes a resonator, tremolo effects, a stereo simulator, panning and even overdrive.

There are 14 different reverb types to choose from, including spring, reverse and gated, but the polyphonic resonator of the Quadraverb is still absent. All the modulated delay effects are very classy, with the chorus and flanging rivalling the best on offer, and though I've yet to hear an electronic box that does flanging as well as two analogue tape recorders, this one gets pretty close. It also does a pretty mean noise‑free Electric Mistress sound too.

Compared with the Q2, there's not a huge subjective difference in sound, but reverb decays are smoother and you can leave a little more headroom without running into noise problems. However, the improvement in signal‑to‑noise ratio is less dramatic than the improvement in low‑level resolution. Editing is straightforward, but the small display means you have to work pretty close up to see what you're doing, so don't mount this unit right at the bottom of a floor‑standing rack!


The Q20 compares favourably with other effects units in the same price range, but this is a tough market with so many 'good enough'‑sounding effects units costing less. In fact, many retailers claim the market for £600 to £1000 effects barely exists in the UK. My own view is that Alesis should have added more DSP power, so that more effects blocks could be combined before the 'game over' message appears. It would also have been nice to have had a MIDI controlled synth‑type filter and a ring modulator. As it is, I feel the effects are a little on the safe side for some of today's musicians, albeit extremely good in quality. I also know a lot of original Quadraverb owners who are still hanging onto those machines because of two or three favourite patches that they can't quite duplicate on anything else. In theory, the Q20 can emulate just about all the effects blocks and configurations of the Quadraverb, and I wouldn't mind betting that if Alesis included a computer disk that would enable patches from the Quadraverb to be translated into their nearest Q20 equivalent, they'd sell a whole lot more.

Those criticisms aside, the Q20 is a superb sounding, easy‑to‑use machine that can be used either as a multi‑effects box or as a really first‑rate main reverb. The comprehensive digital I/O means it can be slotted into systems using ADATs and digital mixers, and the more professional analogue I/O is to be welcomed along with the internal PSU. If you're in the market for a good effects box that falls midway between all those 'good for the money' boxes and those high‑end car‑priced pro units, I'd recommend you give the Q20 a try. Its obvious competitor in this price range is the Lexicon MPX1, which I also happen to like very much, but the two units have quite different characters and effect repertoires, so I'd strongly recommend you try to hear them side by side.

Digital I/O

The Q20 can accept or transmit digital data via two channels of an ADAT light‑pipe or via S/PDIF, and synchronisation is either via the subcode of the digital connection itself, or the unit can be externally locked from a 48kHz master clock such as that provided on the Alesis BRC. Within the Global setup pages of the Q20, the desired pair of ADAT tracks to be addressed via the ADAT I/O can be selected.


  • Frequency Response: 20Hz to 20kHz +/‑0.2dB.
  • Dynamic Range: >92 dB 20Hz‑22 kHz.
  • Distortion (THD+N): <0.005% @1kHz.
  • Crosstalk: >88dB below full scale.
  • Sampling Rate: 48kHz (variable from 40.4kHz to 50.8kHz under external control).
  • Analogue Inputs: Stereo (L/R) Combination XLR/quarter‑inch TRS jacks, balanced/unbalanced.
  • Analogue Outputs: Stereo (L/R) XLR, Stereo quarter‑inch jacks, balanced/unbalanced.
  • Digital Conversion: 20‑bit 256 times oversampling A‑D; 20‑bit, 256 times oversampling D‑A.
  • Digital Input/Output: ADAT Multi‑channel Optical Digital Interface, S/PDIF Digital Interface, BNC jack for 48kHz word clock connection.
  • Factory Preset Programs (ROM): 100.
  • User Programs (RAM): 200.
  • Dimensions (WxHxD): 19 x 1.75 x 7 (inches). (483mm x 45mm x 178mm).
  • Weight: 4.25 lbs. (1.9kg).


  • Well designed operating system.
  • Very classy reverbs and effects.
  • Flexible effect routing options.
  • Comprehensive analogue and digital I/O.
  • Internal PSU.


  • DSP isn't always adequate to combine as many effect blocks as you'd like.
  • The detailed display means you have to be very close to the unit to edit patches.


The Q20 is a very professional‑sounding 20‑bit effects processor with equally professional I/O facilities. It does few things out of the ordinary, but there's no arguing with the sound quality.