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Evolution Synthesis EVS1 Sound Expander

This British designed multitimbral synth expander offers several types of synthesis, free Atari ST editing software, built-in drum sounds, and a low price. Paul Ireson lends an eager ear.

Evolution Synthesis is a new name in the hi-tech music field, and therefore it was something of a surprise to find their first product, the EVS1 expander, promising so much: several different types of synthesis including FM; on-board drum sounds; a free Atari ST editor; and low cost. As it turns out, the surprises don't stop there, and the EVS1 is a far more versatile and attractive unit than it needs to be in order to be a success.

The EVS1 is a 1U high rackmount expander, and it follows a familiar front panel layout: power switch; cursor buttons; Data Increment buttons; Enter button; level control; headphones socket; Bank/Util button; a three-digit LED display; a set of LEDs to indicate what parameter(s) is/are being displayed. Like most budget devices these days, the EVS1 power supply is an external 9V adaptor.

The unit is eight-part multitimbral (ie. it can generate up to eight different sounds simultaneously) and 16-note polyphonic. 100 Sounds are held in memory; 20 of these are user-programmable, and the other 80 are ROM sounds. These Sounds can be used in 20 Groups, each of which is an arrangement of eight Banks. For each Bank within a Group you can select a Sound and set MIDI Channel, Volume, Pan Position, Transpose, Detune, and Lo and Hi Split parameters. You can also specify whether each Bank will respond to various types of controller data: Velocity, Mod Wheel, Pitch Bend, MIDI Controller (assignable), Channel Aftertouch, Pitch Bend, LFO Output. The latter is not a MIDI source, but refers to the internal LFO modulation, and you can therefore turn off the LFO modulation within a Sound in a Group without having to go in and edit the Sound.

The EVS1 seems intended primarily as a kind of 'instant gratification' expander, offering a new set of different sounds to add to those that your existing equipment offers. At the attractive price of £299, and with the inclusion of its onboard drum sounds (two of the 80 ROM sounds are drum setups), it is an obvious candidate as a cheap first expander. The fact that most of the sounds are not user-programmable seems to reinforce its suitability for this kind of role, but when you actually get down to programming the instrument, it turns out to be a surprisingly sophisticated synthesizer in many respects.


Ah yes, editing... As it happens, although you can edit all of the Groups from the front panel, you cannot actually do anything to the sounds. Evolution Synthesis have chosen instead to provide a free (that's F-R-E-E, other manufacturers please note) Atari ST editor/librarian to enable you to do this. A PC version is also available. The editor does not have the sophistication of a dedicated product by any means, but it does have everything it needs to make editing sounds a relatively easy process. You have graphic display and control of envelopes, or if you prefer you can edit the Rate and Level parameters one by one, and there are plenty of keyboard shortcuts to speed things up once you're more familiar with the program.

I said editing sounds is only 'relatively easy' because the manual is little help in actually explaining how the EVS1's synthesis method(s) operate, and therefore a good deal of experimenting is called for before you can really get the hang of things. You can use factory sounds in the 20 user locations as starting points for your own editing, but unfortunately there's no way of copying any of the 80 ROM sounds into the user memories to use for inspiration.


Rather than opt for a single synthesis system, the EVS1 can use several. The unit is all-digital, with 16-bit 44.1kHz D-to-A conversion, and — echoes of the Yamaha SY22 and Peavey DPM3 here — when creating sounds, you start by choosing one of 28 algorithms that use the internal processing power to simulate a variety of techniques. These include Frequency Modulation, Phase Modulation (not a million miles from the Phase Distortion employed on Casio's CZ synths), Ring Modulation, Amplitude Modulation, Width Modulation (not the same thing as Pulse Width Modulation) and Waveshaping. Some algorithms use a single technique — there are several pure FM algorithms — whereas others use two.

The different algorithms contain different elements — let's call them modules. Only Oscillators and Amplifiers are common to all, and others include Waveshapers, Ring Modulators, Width Controls. The algorithms and therefore the elements that are in use determine the nature and number of the parameters that can be edited, although essentially you simply set pitches and select waveforms for oscillators (except in those configurations that only allow sine waves), and specify how you want the four envelopes and several other modulation sources to affect pitches, amplitudes, and so on. Because oscillators may be used in quite different ways in different algorithms (eg. as an FM operator in one, and as an analogue-style oscillator in another), changing an oscillator's pitch may create radically different effects depending on which algorithm you have chosen. Oscillators can be transposed up or down 64 semitones (below or above the nominal keyboard pitch) or can be set to a fixed pitch within that same range.

One of the EVS1's strengths is the depth of its modulation facilities. Firstly, each of the four envelopes is not hardwired to anything — instead, for each envelope, you specify modulation depth and routings to two destinations, which can be any of the algorithm's mod destinations (see accompanying panel). In practice, this means you can modulate just about everything that you might want to in an algorithm. Two LFOs per voice can also be used: each LFO has variable waveform, delay, and speed, and can be used to modulate any two destinations. Finally, there is a modulation matrix, through which five performance sources can modulate any four user-defined destinations. The sources are Keyboard Scaling (variable depth and breakpoint), Velocity, Aftertouch, MIDI Controller, and Mod Wheel.

So, plenty of sources, and as you work through the algorithms, you find that you can modulate pretty well everything you want to. Now is probably the best time to look at the algorithms, and see how they work.


Algorithms 1-4 are all 4-operator FM stacks. Here the EVS1's oscillators become FM operators, and use only sine waves — your control over the sound is exercised by changing the pitch and amplitude of the four oscillators. Algorithm 1 is a 'straight through' stack, with only oscillator 1 being output as an audio tone. Algorithm 2 has two modulators in parallel modulating a carrier, which in turn is modulating a final (audible) carrier. Algorithm 3 has two modulator-carrier stacks in parallel, and Algorithm 4 has a single modulator operating on two audible carriers, with the third oscillator output in parallel. Some old FM tricks can be applied, such as fixing the pitch (frequency) of a modulator to create 'formants'. Of course, you have to think in terms of conventional musical intervals rather than FM ratios, because you are setting the pitch of each oscillator just as you would in a non-FM synth.

Algorithms 5 to 8 are Phase Modulation (PM), and use architecturally identical stacks to the four FM algorithms. Phase Modulation differs from FM (Frequency Modulation) in that rather than the frequency of the carrier sine wave being modulated, its phase is modulated. Casio's CZ synths used this technique, but went about it rather differently by offering the programmer a choice of waveforms that the synth would be able to produce by distorting a sine wave — the process by which the sine wave became a more complex waveform was hidden from the operator. Here, you are thrown in the deep end with four sine waves, and it's up to you to find out how to manipulate their amplitudes and pitches to produce results.

PM actually sounds a little like a mellower version of FM. Raising a modulator's pitch produces the same kind of effect as it would in FM — higher frequency overtones — but the range of sounds is altogether more subtle, and it's perhaps less easy to find yourself out of control and producing a sound that you really don't like.

Algorithms 9 to 12 combine FM and PM. Again, the same four stacks are used. What seems to be happening is that oscillator 4 performs frequency modulation on whatever it is routed to in the algorithm, and the other connections are all PM.



Square smoothed
Square with resonance
Sawtooth with resonance
Wind 2
Vocal aah
Vocal ooh
Bass sustain
Smooth text
Marimba attack
Piano rough
Piano B
Church organ
Wind sustain
Bass sustain
Smooth string
Noise 3
Noise 4
Hard clip
Soft clip
Smooth brass 1
Smooth brass 2
Smooth bass
Smooth sawtooth

The remaining 16 algorithms don't split quite so easily into sets. Algorithm 13 has three oscillators in parallel, and any of 32 stored waveforms can be used for each oscillator. The waveforms (see panel) are all single cycle types. There is no filtering available, so timbral changes are created by fading one oscillator up and another one down. Algorithm 14 also has three oscillators with switchable waveforms, but two are arranged in an FM stack, so you can try your hand at FM with waves other than sine. Algorithm 15 is the same, but with PM instead of FM.

Wherever a waveform is chosen in an algorithm, the choice of waveform can be a modulation destination — you can change the waveform during the course of a note. This is how wavetable synthesis works, and although the 32 rather diverse waves that are available here hardly constitute a wavetable, you can create some great effects by messing about with this facility.

Waveshapers are used in Algorithms 16, 17, and 18. Algorithm 16 has twin Waveshapers in parallel, which take the output of a sine wave oscillator and distort it in a way that is determined by the shape of the waveform chosen for the Waveshaping module. Any of the standard 32 waves can be chosen, and some of the waves have been included specifically for their suitability for use in waveshaping — Soft Clip and Hard Clip both simulate a kind of distortion. (For more details see the three-part series of articles on Digital Signal Processing: SOS Oct-Dec 1989.)

The important thing, of course, is what it sounds like. Distorting the input wave in this way changes the harmonic content, and varying the level of the input signal (there are amplitude stages before and after the Waveshaper module) can produce continuous changes in harmonic content as well as output level, which is also modified by a dedicated amplifier module. Again, you have to experiment to get a feel for what's going on, but it is possible to create an effect with the Waveshaper that is similar to sweeping a resonant filter, although the sound has a more aggressive edge to it.

Algorithms 17 and 18 have, respectively, an FM and a PM stack passing through a single Waveshaper module. The carrier can also be heard directly via an amplifier module.

Amplitude Modulation (AM) is used in the next two algorithms. In algorithm 19, an oscillator playing any wave can be amplitude modulated by the output of a ring modulator. One of the inputs to the ring modulator is a second 'regular' oscillator, and the third is a sine wave. The first oscillator can also be Width Modulated, but more of this in a moment. Algorithm 20 has two simpler amplitude modulation units in parallel.

The effects of amplitude modulation are much easier to predict, but equally the technique does not have the potential of FM for creating such a diverse range of sounds. New harmonics are created at frequencies that are the numerical sum and difference of the modulator and its source.


The Width Modulation that I mentioned a moment ago is used in algorithm 21, where two width mod stacks are used in parallel. In each, you are given a single oscillator (which can play any wave) and amplifier module, plus a third Width module. The Width module has a frequency parameter, and sweeping this up and down produces an effect very similar to that of sweeping the frequency of the driving oscillator in an analogue synth when another oscillator is synced to it.

The 'width' referred to in the name of this kind of synthesis is in fact the proportion of the oscillator's waveform that is actually used — rather than simply repeating the whole waveform, a part of it, or a whole cycle and then a part of a cycle is repeated. The fundamental frequency of the sound is always that of the oscillator that is being modulated, but the harmonic content is determined both by the waveform that is chosen and just what portion of the waveform is repeated. This is very much what happens in analogue hard sync, hence the similar sound.

Algorithm 22 is a rather boring one, and simply has four sine wave oscillators in parallel. Algorithm 23 and 24 are both FM stacks with feedback, where any wave can be used by the oscillators. Algorithm 25 has a single oscillator performing FM on itself via a feedback loop, in parallel with a width modulation stack. Algorithm 26 (Vosim) is a slight modification of the one-oscillator-with-width-modulation arrangement, in which a Decay module allows you to control a separate set of harmonics. 'Vosim' is an abbreviation for 'voice simulation', and although it is loosely based on a technique for achieving exactly this, in the drastically cut down form in which it appears on the EVS1, it's really only a slight variation on Width Modulation.

Algorithm 27 has a two oscillator Phase Modulation stack in parallel with a filtered noise source. Unfortunately the filter has a very shallow slope, and sweeping the cutoff frequency down (which, rather confusingly, requires you to apply positive modulation) sounds more like lowering the volume. The final algorithm is a four oscillator Phase Modulation stack, with a single feedback loop.

All in all, the 28 algorithms cover a good deal of ground and provide you with some quite varied synthesis techniques. The modules are always very simple — at most you can change only two parameters on any module — but the ways in which they can interact are not, and the excellent modulation facilities enable you to make the most of the algorithms. In algorithm 18, for example, at the most basic level you can use amplitude and pitch modulation on oscillators 1 and 2 in two-operator FM synthesis. Modulating the input level into the Waveshaper module creates further timbral changes, and you could even modulate the wave allocated to the Waveshaper module.


With all this going for it, it's a real shame that the EVS1 doesn't offer more room for user sounds, or perhaps a RAM card slot. The preset sounds are very usable, with only about five 'effect' type sounds that, inevitably, will only ever be used once or twice. The selection is stronger on strings, synth pads, and some rather good basses, than on acoustic imitations.

The two drum setups (same sounds, different keyboard mapping, one of which conforms to the Roland standard) feature excellent sounds. The choices are good — modern, tight, and aggressive — and the sound quality certainly belies the low price of the EVS1.

Still on the subject of sound quality, the synth sounds are also good, although many of the techniques do introduce FM-style digital noise. One minor criticism I would level is in regard to the envelope resolution. If an envelope is slowly sweeping over a large range, it is often all too easy to hear the digital 'steps' as the envelope level rises or falls. This is definitely a problem at source, rather than at the modulation destination, although in many cases problems can be reduced in the following way. Whenever you assign an envelope to modulate any destination, you must set a modulation level. When programming your envelopes, you may find that you tend to leave the modulation value unchanged, and reduce the levels at each of the envelope stages. The effects of stepping will be less obvious if you increase envelope level values as much as possible (thereby using more of the envelope generator's resolution) and reduce the modulation level.


As I said at the start, the EVS1 is a surprising unit. It undoubtedly succeeds in offering a decent variety of 'off the shelf' synth sounds to supplement those of a modest keyboard setup. However, the ways in which it produces these sounds are quite varied — the fact that there are several is odd enough — and for this reason the EVS1 will prove a highly rewarding box of tricks for programmers. Provided you can live with slight limitations, such as only 20 user memories and the envelope resolution, the EVS1 offers a great deal of off-beat, in-depth synthesis for you to explore.


£299 inc VAT.

Evolution Synthesis Ltd, (Contact Details).


Oscillator frequency
Wave (select, oscillator or waveshaper)
LFO 1 speed
LFO 1 depth
LFO 2 speed
LFO 2 depth
EG Rate Output (amplitude module)
Waveshaper In (amplitude)
Waveshaper Out (amplitude)
Ring (frequency of sine wave input to ring modulator)

Also featuring gear in this article

Previous Article in this issue

Dave Stewart's Music Seminar

Next article in this issue

Summer 1990 NAMM Show Report

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Aug 1990

Donated & scanned by: Mike Gorman

Review by Paul Ireson

Previous article in this issue:

> Dave Stewart's Music Seminar...

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> Summer 1990 NAMM Show Report...

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