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Cheetah MS6

Synth Expander

The long-awaited, rack-mounting, multitimbrol, budget analogue synth expander from Cheetah has arrived. Simon Trask turns on and trips out.

With old-style analogue sounds making something of a comeback, Cheetah's programmable multi-timbral analogue rackmount could be a timely release. And at just under £300 it could be a killer.

SOMETHING IS STIRRING in the jungle. Spotting a gap in the undergrowth (sorry, market), Cheetah have come up with the MS6, a six-voice, multi-timbral analogue synth expander with front-panel programmability for £3OO. Do you think this is some kind of joke? No. Read on - you could be doing yourself a big favour.


THE MS6 GIVES you 320 ROM sounds, 96 non-volatile RAM sounds and 64 Performance memories - the latter being used for creating multi-timbral setups of up to six independent parts. These are organised into eight banks, with the Performance memories in Bank eight and the RAM Patch locations in Banks six and seven.

The sounds can respond to both attack velocity and channel aftertouch via MIDI; you can set a single MIDI receive channel (1-16) in Patch mode and any combination of up to six channels in Performance mode. The MS6 responds over an eight-octave note-range (24-119) and will respond to pitch-bend, modulation, volume and sustain controllers.

Front-panel operation is fairly straightforward: along with the reasonably informative LED window (which variously displays things like Bank and Patch numbers, or parameter and value numbers) you get an eight-button numeric keypad, value +/- buttons and Bank and Edit select buttons. The rear panel is even more straightforward, consisting of MIDI In, Out and Thru sockets and a single audio output jack.

As you might guess, all Patch and Performance parameters are identified by number (which you tap in on the keypad). Fortunately, Cheetah have included a complete parameter listing on the top panel of the MS6 - not much use if you're slotting the expander into a rack, but a damn sight better than nothing if you're not. Fortunately, Cheetah have organised the parameters in a fairly logical fashion, making it easier to memorise the numbers. After a few prolonged editing sessions you'll probably find them sinking in, and eventually becoming automatic.

Logically enough, repeated pressing of the Bank button steps you through the Banks, while Patch numbers within each Bank have to be entered via the eight-key numeric keypad. Patches within the current Bank can also be selected via MIDI (unlike on the Matrix 1000, there is no means of selecting Banks via MIDI). However, as Cheetah use the awkward 11-88 numbering system, some quick mental conversions may be called for (alternatively, you can refer to the conversion chart thoughtfully provided in the back of the manual). Remember that when you're in Bank eight you'll be calling up Performances rather than Patches.

Sounds and programming

CHEETAH HAVE ADOPTED a policy of grouping like sounds. Thus, for instance, you'll find string sounds in Bank one, piano and brass sounds in Bank two, and bass and lead sounds in Bank four. The overall standard and consistency of programming isn't up to that found on Oberheim's Matrix 1000 (reviewed MT, August '88), the nearest thing the MS6 has to a competitor. But then, unlike Oberheim, Cheetah don't have a large user-base to draw on for a cream-of-the-crop compilation - yet. The company seem to have programmed sounds which they personally like, but which of course may not be everyone's proverbial cup of tea. However, the idea is that you have plenty of starting points for tailoring your own ideal sounds. The first things you'll probably find yourself doing will be altering the amplitude envelope, adjusting the velocity responsiveness and perhaps lowering the filter cutoff a little (I found myself doing this on many of the ensemble string sounds, which were a little too buzzy for my liking). Not exactly overtaxing on the old programming skills.

Keyboard sounds are, on the whole, not the MS6's strong point (nor are they the Matrix 1000's, incidentally), but the clean, hard-edged acoustic/electric piano of patch '2.14' and the delicate, spindly harpsichord of '5.68' are sounds worth playing around with. There are plenty of string pads to work from, including the deep, resonant drone-strings of '1.48' and the smooth strings of '1.42'; as you might expect, the MS6 is capable of producing the sort of string sounds you probably won't get from yer average digital synth.

"It's not every day a company - let alone one new to the field of synthesis - brings out a quality programmable, multi-timbral analogue synth expander for £300."

The MS6 is also capable of producing some spunky synthbass sounds, though on the whole you'll need to do a bit of work to get them (however, there's the odd acid-styled bass, such as '7.26' with its resonance and LFO mods). Atmospheric sounds can be eerie and floating (such as '3.52'), dark and growling (such as '3.43' and '7.34') or all-round weird (get programming; pushing a system to extremes always strikes me as a good way of getting to know it; the MS6 won't let you down here, especially with its powerful - some might say vicious - filter resonance).

The voice architecture of the MS6 is essentially the familiar oscillator-filter-amplifier model, with two DCOs, one 24dB/octave filter, two ADSR envelopes and one LFO per voice. All in all there are a maximum of 59 parameters governing each Patch. One particularly handy feature is the ability to store an overall volume level for each Patch; you can also adjust volume in Play mode using the +/- buttons.

DCOs A and B both provide a choice of square, triangle and sawtooth waves, while DCO B additionally offers noise; the square wave can be modified, independently for each DCO, by adjusting its pulse width - this in turn can be a static or dynamic adjustment. Each DCO can be switched to one of four octaves, and can additionally be tuned to any semi-tone within the octave, while DCO B can be detuned against DCO A +/-93 cents in three-cent intervals.

The pitch of each DCO can be controlled by the LFO, with depth independently controllable but rate defined by the setting in the LFO section; it's also possible to impose a pitch envelope on each DCO, with envelopes one and two individually assignable. Pitch-bend range (an octave maximum) can be set independently for each DCO, as can the control source (which can be the pitch-bend wheel or channel aftertouch).

The MS6 scores heavily with its filter section, which uses the famous Curtis chips as found in Sequential's Prophet 5. As well as being able to set filter cutoff frequency and resonance amount, you have the option to dynamically control the cutoff from the LFO, envelope one or two, and channel aftertouch (with depth settings in each case). As you can set overall velocity sensitivity and attack-time velocity sensitivity independently for each envelope, it follows that you can control the filter envelope from velocity as well as aftertouch. In both these cases (but not LFO filter modulation) you can invert the response, so that for instance a hard keystrike will close the filter.

Envelope one is hard-wired to controlling the amplitude of both oscillators, but can also be used to control filter cutoff, pulse width and pitch (in the latter two cases, of either or both DCOs). Envelope two can be used to control the same features excepting amplitude. Key follow can be set independently for each envelope; with this on, decay and release time shorten as you play higher up the keyboard (the degree of change can be set on a scale of 0-15). As this is typically what happens with plucked and struck instruments, it's a useful feature to have. Potentially useful for percussive sounds is a "sustain switch" feature, which allows you to decide independently for each envelope whether or not the sustain phase will be ignored, with the envelope going straight from decay to release.

"Pushing a system to extremes always strikes me as a good way of getting to know it; the MS6 won't let you down here, especially with its powerful filter resonance."

The LFO section allows you to choose from triangle, sawtooth, square and random waveforms, with parameters governing delay-time and frequency together with pitch- and filter-modulation depth. Additionally you can select pitch-bend wheel or channel aftertouch as the modulation source for each destination. Unfortunately you don't have the option to reset each voice's LFO when a new note is played, but I for one can live without that on an instrument of this price.

Although the MS6's oscillators are factory-calibrated and digitally controlled. Cheetah have been ultra-cautious and included a calibration routine. This should be used with care, as calibration takes some three-and-a-half minutes and cannot be stopped once started; it's also a good idea to ensure your amplification is turned down low, as the MS emits some rather piercing sounds during the course of this ritual. However, it's extremely unlikely you'll need to use it; I certainly never had any problems with tuning stability (but then I'm a pretty stable sort of person).

There's good news for those of you who like to play around with filter cutoff, resonance and God-knows-what as part of a performance; the MS6's Patch parameter edits change in real-time. But being a digital access system, the MS6's editing only allows you to alter one parameter at a time. What's more, tapping in parameter numbers and adjusting +/- buttons isn't in quite the same league as being able to twiddle knobs or waggle sliders. However, with practice and familiarity you can get to move around the synth's voice architecture relatively quickly.

Creating a Performance

THE MS6's 64 programmable Performance memories allow you to define up to six Instruments, each consisting of settings for Bank and Patch, number of voices (there's no dynamic voice allocation), low and high note limits, MIDI receive channel (1-16) and patch volume. To call up these memories (either from the front panel or via MIDI) you must first step through to Bank eight.

Essentially there are two ways to make use of the Performance memories: either as a means of playing up to six independent sounds, or as a means of creating "Super Patches" by layering a maximum of six Patches at a time. However, you aren't able to edit Patches in Performance mode, which does make it difficult, but not impossible, to edit one sound with reference to others.

Cheetah have opted for the layered-sound approach, enabling them to build up some powerful composite sounds which you should definitely check out in order to fully appreciate the MS6's capabilities. However, unless you only want to use Performance mode for creating lead, bass or "orchestral" monophonic sounds, the chances are that you'll feel the pinch of only having six-note polyphony to start out with. This is where the MS6's MIDI Overflow mode comes in handy once again, because it overflows (retransmits via MIDI Out) any notes it can't handle internally on each active MIDI channel; hook up another MS6 and you've got a more reasonable 12-voice polyphony, another one again and you're up to 18 voices (for a not unreasonable £900). But it's not good news all the way: as with Patch mode, only notes overflow via MIDI - controller information and patch changes don't get past the first post. Better news is the fact that pitch-bend, modulation, volume and sustain on the "master" MS6 can be responded to on all active channels, and will only affect the relevant voices.

"The extra sophistication of the Matrix 1000's voice architecture allows it to reach into areas that the MS6 can't, but in many ways I'd say they're pretty evenly matched."

Further fattening up of a composite sound can be achieved by detuning the individual Patches against one another. However, detuning is a function of individual Patches (where you detune oscillator B against oscillator A). This means that if you want to detune, say, four layers of the same Patch, you'll have to literally make four copies of the Patch in the RAM Patch memory. What's more, as you can't edit sounds within Performance mode, you'll have to keep swapping between Patches and Performances, not forgetting to store your Patch adjustments each time, as you edit your detunes. Still, where there's a will there's a way, and it really is worth a spot of effort for the sort of results you can achieve (which, remember, can be called up instantly by selecting the appropriate Performance memory once stored).

System Exclusive

PATCHES AND PERFORMANCE memories can be SysEx bulk-dumped via MIDI, a process which takes under five seconds, allowing you to build up large sound libraries on relatively cheap floppy disks. SysEx dumps can be initiated from the MS6's front panel, and no handshaking procedures are required for transfer in either direction. For those of you counting your figures, a Bulk dump of Patches takes 8646 bytes and a bulk dump of Performances 3846 bytes.

Although it should be possible to produce editor/librarian software (Cheetah include the necessary SysEx details in the manual for those who want to try their hand), it does seem that only bulk memory dumps are possible, so individual parameter edits via SysEx might be a bit unrealistic.


CHEETAH SHOULD FEEL proud of themselves for what they've achieved here. It's not every day a company - let alone a company new to the field of synthesis - manages to bring out a quality programmable, multi-timbral analogue synth expander for £300.

The MS6's only real competitor is Oberheim's Matrix 1000 (reviewed MT August '88), which costs some £150 more, isn't programmable from the front panel and isn't multi-timbral. However, the Matrix offers a massive 1000 preset sounds (800 ROM, 200 RAM) and can be programmed remotely using a Matrix 6/6R or a computer-based editing package. The 1000's voice architecture is more sophisticated than that of the MS6, and its preset sounds (the pick of the crop from Matrix 6/6R users) are uniformly better than the sounds which Cheetah have provided. But the point about the MS6's sounds is that they provide you with starting points for tailoring a variety of sounds to your own personal taste. Not having been able to place an MS6 and Matrix 1000 side-by-side, I'm loath to make any direct comparisons. Obviously the extra sophistication and complexity of the Matrix's voice architecture allows it to reach into areas that the MS6 can't, but in many ways I'd say they're pretty evenly matched. As far as the MS6's voice architecture goes, Cheetah have arrived at a very successful balance of flexibility versus complexity, and personally I found programming the expander a lot of fun (how often can you say that about a synth nowadays?). You get the distinct impression that Cheetah have thought long and hard about what they wanted to fit in, and then put in as much as they could for the price they wanted to charge. The MS6 doesn't have the front-panel immediacy of the old knobs-n-sliders synths, but by going for number-specific parameters Cheetah have at least ensured that, with practice, you can edit pretty quickly. On the practical front, the casing is fairly rugged and the unit I had (a production model, incidentally) exhibited no overheating problems despite being left on for a couple of days.

The MS6's six voices might not seem much in this day and age, but by using the expander's Overflow mode you can increase this figure by adding further units (£600 buys you two MS6s and 12-voice polyphony).

Any synth player enamoured of analogue sounds should be able to find a place in their rack for at least one MS6. And if your digital synths aren't giving you all the depth and warmth of sound you'd like, Cheetah's expander offers the ideal solution. A serious product at a seriously low price.

Price £299.95 including VAT

(Contact Details)

Also featuring gear in this article

Previous Article in this issue

World Machine

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Yamaha YS200

Music Technology - Copyright: Music Maker Publications (UK), Future Publishing.


Music Technology - Nov 1988


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Gear in this article:

Synthesizer Module > Cheetah > MS6

Gear Tags:

Analog Synth

Review by Simon Trask

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