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Alesis S4 Quadrasynth

64-voice Sound Module
Published November 1994

Dave Crombie gets to grips with Alesis' Tardis‑like synth module and finds out that the inside is a lot bigger than the outside.

For me, the QuadraSynth is one of the more important new instruments to appear on the synth market for quite a while, not because of astounding new technologies, hi‑tech reworkings of old principles (à la OB*Mx, Wave, VL1, etc) or even because it sounds radically different to its rivals, but rather because it combines great power and sonic integrity at a very reasonable price.

It was obvious when Alesis announced their Quadrasynth that a module version would follow, and though the S4 module is considerably smaller than its keyboard counterpart, it is no less impressive. Other than the lack of keyboard and the loss of the volume knob, there are a few differences between the S4 module and the S5 keyboard (reviewed by Martin Russ in May 1994 SOS), but in view of the similarities, this review should be read in conjunction with the S5 review.

The S4 is a 64‑voice polyphonic module which also features percussion sounds. Voices can be stacked up to your heart's content as long as you're prepared to sacrifice some polyphony, and for many users, the S4 with a master keyboard and sequencer would make an excellent workstation. For those with existing MIDI systems, the S4 is an attractive additional sound resource. Even for a 1U module the S4 is small — a mere six inches deep — and very light, although this is in part due to the fact that it has an external power supply, linked by a 4‑pin DIN lead.

The voice architecture of the QuadraSynth is of the sample + synthesis variety, though there are no resonant filters.

  • At the base level there are digital samples of acoustic or electronic sounds. These samples are arranged into 16 banks: Piano, Organ, Keyboard, Synth, Waves, Bass, Guitar, Brass, Woodwind, String, Ensemble, Ethnic, Voice, SoundFX, Drums and Percussion.
  • Samples can be processed (filtering, amplitude and pitch modulation and so on): a processed sample is known as a Sound.
  • A Program comprises up to four Sounds, which can be split, layered, or assigned specific key ranges; in addition a Program has assigned to it any one of 256 preset or programmable Effects Patches. There are 128 preset and 128 user‑programmable Programs.
  • A Mix consists of up to 16 Programs, each with its own MIDI number, and a master Effect Patch.

The S4 may be used either in Mix mode or Program mode, depending on how you like to work; 1‑Sound Programs allow 64‑note polyphony in Program mode, though 4‑Sound Programs obviously reduce this to 16 notes.

Sonic integrity is assured by the use of 16‑bit, 48kHz samples. Each sample varies in span; individual piano samples span just three or four notes in the middle octaves, while other sounds may be less generously deployed. Though the synth is entirely digital, the signal path is quite conventional, with the oscillator/waveshaper producing the sample at the desired pitch, followed by filtering and then dynamic amplification (envelope generation). The Sound is then routed to either the main stereo output or the auxiliary stereo out; the latter can be via the effects processor. As stated, four Sounds make up a Program and each Program, not Sound, has its own Effect setting.

The S4 has a comprehensive Drum Mode. Drum Samples are stored with the other samples and can be used just as if they were normal samples, but in Drum Mode it is possible to create your own kit of up to 82 different samples and to map them as desired.


Synthesizers, like cars, are all tending towards the same 'shape' (building‑block‑wise). One area that still offers room for manoeuvre is that of modulation, a key area when evaluating the power of a synth. There are modulation Sources — LFOs, Envelopes and so on — and there are Destinations, such as Filter Frequency and Amplitude. The trick is to assimilate a large number of useful sources and then route them to the destinations as efficiently as possible, while still retaining flexibility and ease of use.

In the modulation sources department, the S4 is not lacking. Further to all the usual sources, including polyphonic aftertouch and note‑off velocity, is 'Trigrate' which analyses the speed (not velocity) at which you play notes on the keyboard. Using this, you could, for example, reduce the envelope attack time of a sound when you play the keyboard faster. There are 32 modulation destinations (very comprehensive) and there's even scope to control the portamento rate and the amount of signal sent to the effects from a modulation source.

The S4 uses a six‑way modulation matrix to set up modulation routing; up to six source‑to‑destination links can be created, using a separate edit page for each link. It all adds up to an extremely efficient and powerful modulation section, offering a wide range of functions but utilising them in an understandable way. It would have been nice to have more than six links available, but even so, there's plenty of flexibility.

One further facility worth mentioning at this stage is the Tracking Generator. This takes a modulation source and routes it to a destination independently of the Modulation Matrix. Its purpose is to take a linear source such as the mod wheel, which has values ranging from 0% to 100%, and re‑map the output. Using this, a variation of a linear input, say from 30% to 50% to 70%, could produce a non‑linear output going from 90% to 10% to 50% — the Tracking Generator interpolates so the transitions are smooth. This concept opens up a wealth of modulation possibilities.


I'm not usually a great fan of on‑board effects units, but here the effects are versatile, quiet and clean, and can be considered as being integrated into the synthesis process. You would expect a good effects section from Alesis and you won't be disappointed. Could there be Quadraverb II technology behind the front panel?


When you buy a synth module, your priorities are probably sound generation capabilities and price, with functionality coming a close third. On the sound front, the S4 is great, with incredibly clean, crisp and bright Programs (more Japanese in character than American, I feel). If there's a weakness, it must be the lack of resonant filters, which is particularly serious if you are producing dance/techno or retro synth music. Alesis are usually on the ball in matters contemporary, but this time they've spent their processing power on polyphony instead. Still, if you have a spare grand and an unused 1U slot in your rack, the S4 provides a very attractive way of filling it.


  • 16‑bit resolution samples
  • 48kHz Sample Rate
  • 16Mb of Sample ROM
  • 128 Preset Programs
  • 128 User Programs
  • 128 Preset Effects
  • 128 User Effects
  • 100 Preset Multitimbral Mixes
  • 100 User Multitimbral Mixes
  • 64‑note Polyphonic (1‑Sound Programs)
  • 4‑way Multi‑effects
  • 4 Quad Knob Controllers
  • Stereo Output jacks
  • Stereo Aux. jacks
  • ADAT Optical Out.

The Control Panel

The layout of the S4's front panel is intelligent, but could be easier to use. It centres around a nice clear back‑lit custom LCD display (which is virtually the height of the rack and five inches wide), and handles a lot of information — so much so that some of the text is incredibly small. On the positive side, the display is exceedingly sharp.

The diagram shows the display, with most of the elements shown ON. The PROG and EFFECT values are always shown, no matter what page is selected. To the right of the display are four control knobs — the 'Quad' knobs, as Alesis call them. Associated with these are four Select buttons, and a two‑way (increment/decrement) Value button. To the left of the display are eight parameter selection buttons with two‑way Function and Page up/down buttons. You select the Page of parameters to be edited from the controls on the left and change values with the controls on the right.

Back to the display, where the right hand alpha‑numeric section shows the name of the currently selected Mix, Program, Effect or Parameter, whilst the four bar‑graphs (lower right) indicate the respective settings of each of the Quad Knobs. Although these bar‑graphs make it easier to see the settings of the knobs at a distance, they are somewhat confusing. The display is also a bit sluggish to update, making it difficult to quickly home in on a specific value.

Alesis have been quite inventive with their user interface, trying to get away from the basic single data entry mode. In some ways they've cracked it. In others they've broken it!


The Programs and Mixes seem to be slightly different to those on the S5, though there are many that are common to both, and some that have been improved on the S4. Overall the sounds are very impressive, without the muddle that one tends to get with low‑pass filtered samples. Touch sensitivity (including note‑on and note‑off velocities) and additional mod wheel control add to the expressiveness of certain sounds, for example, the 'MoodyFlute' (Preset 14) where the mod wheel is used to add an extra chiff to the attack. Another example is the the excellent 'SaxSection' (Preset 24) where both vibrato and filter cutoff are controlled simultaneously by the mod wheel. The brass sounds and strings are quite superb, though many of the brasses utilise a short echo to fatten/double themselves up, which some might consider to be cheating.

Most types of sound, with the exception of a straight grand piano, are extremely well catered for. There are various other pianos, though — a rather brash 'Ballad Pno' (Preset 11); Pianoohs (Preset 21) — you can guess ‑‑; 'ArenaPiano' (User Program 91) — a bright, clean baby grand marred by just a hint of a rather inconsistent harmonic; and an electric grand entitled 'Fast Piano' (User Mix 40). I understand that one of the first ROM cards to be released will feature a dedicated Grand Piano ROM with vast amounts of memory assigned to acoustic piano samples.

The only real problem with the sounds is the lack of resonant filtering, which precludes a whole class of real‑time variable timbres.


  • Fantastic sound quality.
  • 64‑note polyphonic.
  • Good value.


  • No Resonant filter.
  • Sluggish display update.
  • External PSU.
  • Program or Mix Number display is rather too small to see at a distance.


A classy‑sounding module; few synths can produce such a range of uncoloured sounds with such depth and clarity. A most impressive, if slightly unexciting, unit.