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Korg MS20

Article from Music Technology, June 1989

This month's trip down memory lane takes us to Korg's MS20. Greg Truckell reacquaints himself with an analogue synth that may be better suited to use in 1989 than 1979.

While the major manufacturers play digital mix 'n' match with their gear, the hip musician is moving into analogue technology — and discovering there's more to old synths than the Minimoog and Bassline.

SOME MUSICAL INSTRUMENTS, particularly synthesisers, are instantly appealing. Others, it must be said, are instantly appalling. As far as first impressions are concerned, the Korg MS20 comes closer to the latter category than the first. I can remember going through the handbook and setting up all the patches of my new synth and being increasingly impressed by how unlike anything else the Korg MS20 sounded particularly when it was supposed to sound like something else. But after living with my MS20 for about seven years. I've become convinced that it really is a remarkable machine. It's come in for a fair bit of criticism over the years; "thin", "nasal", "reedy"... You've heard it all before, and all it tells you is that the MS20 doesn't sound much like a Minimoog. Well, I've yet to hear a fat-sounding oboe, but that doesn't keep them out of the orchestra or the recording studio. Forget easy big fat bass and solo lines for a while. Even in the minimalist pop musics of today, there's space for sounds other than "fat" basses and "thick" lead lines. You can get fat sounds out of the MS20 — if you work at it — but where the little Korg excels is in a different sort of cutting timbre: a thinner sound capable of getting through a smaller gap in the mix.


THE MS20 IS a distinctly odd beast to look at; three octaves of keys and a generous 35 knobs to twiddle on a steeply-angled front panel. To the left of the keyboard is a single modulation wheel and a small button. There's also a rather intimidating 35-hole jackfield. This can be quite confusing at first, and is printed with an array of interconnecting lines, arrows and little boxes to ensure it remains a mystery for as long as possible.

The Korg MS series approach to synthesis is probably best described as semi-modular. "Conventional connections" are made by hardwired internal connections, but these can be overridden or supplemented by plugging a patch lead into the relevant socket — like the system you might find on a normalised audio patchbay. The diagrams printed on the jackfield are supposed to explain what the hardwired connections are. While less flexible than a fully modular system, the Korg system is easier to get to grips with, less expensive and more compact. It doesn't make the MS20 a pretty machine, but it makes good practical, technical and ergonomic sense.

Like many odd beasts, the MS20 comes from an odd family. The MS10 was a little brother in all respects (though it would make a useful addition to an MS20). The MS50, a single-oscillator job like the MS10, had no keyboard (one of the earliest expander modules), but did have a few unusual modules — for example, a voltage divider, voltage inverter and a voltage-controlled LFO, where a CV from any source could control the frequency of the LFO. Another relative was the SQ10 24-step analogue sequencer, a useful enough box of knobs with a clock inside it, and a number of modulation pedals, with and without LFOs. The SE5OO was a tape echo unit with a CV input for the tape speed seriously whacky, though sadly guaranteed to glitch if you sent it anything other than very gradually changing CV signals. One of the most useful black boxes was the MS02 interface, which converted both ways between the standard 1Volt/Octave system used by most other manufacturers and Korg's more stable Volts/Hz system, also converting between positive and negative-going gate signals. Although Korg's MS02 handbook said that you should give the MS02 a ten-minute warmup and expect the occasional need to retune, I found mine to be perfectly stable as were the MS series in general. Korg got round the problem of using inherently unstable log/amp circuitry by using a different keyboard algorithm.

While the MS02 interface opened up the possibilities of using the MS20 with, for example, Roland sequencers (like the MC202 and TB303) there was another little module, called the External Signal Processor (ESP), which was available separately, but was also a standard feature on the MS20. This module was used to amplify and analyse any input signal, allowing the MS20 to derive CV information from other instruments — but don't be tempted to think you could take your Strat and double it with exciting synth lines for the ultimate in pre-MIDI solo; acoustic events in particular, and even electronic instruments like guitars, are too complex for proper conversion into bunch of analogue CVs. Pitch-to-CV conversion requires analysis of the input in terms of simple waveforms, where the loudest harmonic by far is the fundamental. In practice you might get away with just under one octave of control, if you play slowly and only one note at a time. Play two notes or more at a time and you get garbage.

The ESP sections most interesting and useful applications lie in deriving a trigger from any input, whether it be acoustic, such from a click track or a kick drum off tape, or electronic, such as a trigger from a drum machine or sequencer. Using this method to trigger the MS20's filters and envelopes. they can be used to process any audio input — there is an external audio input before the filters and envelopes. You could also use whatever your source of spikes might be just to trigger the MS20, and control the pitch from the keyboard, or from a sequencer. Suppose you had an MC202 controlling the pitch of the MS20 via a MS02 interface, but with the MC202 running independent of the tempo of the song. With the MS20 triggered from a spare drum machine output, or a spare audio output, and a handful of pitches derived from the main key of the song programmed into the MC202, you'd have instant pseudo-random selection from a user-defined range of pitches, coming in precisely on the beats you want. This is an example of the sort of effect you can get from algorithmic composition software like Intelligent Music's M or Dr T's Programmable Variations Generator — only with knobs.

It's also possible to regard the MS20 as an analogue signal processor. Effects like swept resonance gates, or resonant phasing, are easily set up. Effects quite unlike anything possible with other techniques are also worth exploring. For example, take any input which has some sort of sustain to the sound. Send this through the MS20's ESP section and trigger the MS20 from a sequence using whatever techniques you fancy to control the filter cutoff frequency. With short envelopes and resonant filters, this can create stuttering, staccato timbral sequences, chopping up your source instrument and creating something quite new. Having mentioned timbral sequences (in which the interest derives from rhythmic changes in timbre rather than pitch), it's worth adding that the MS20's filters respond to CV signals in the range -5 to +5V, which means that a CV from any analogue sequencer or micro-composer can control the filters, without the need for accurate conversion required for pitches. There's nothing to prevent you connecting the MS20 to anything with CV sockets. Rope in an adding amplifier (as found on the MS50) and you can even hook into the CV pedal input on Ensoniq's ESQ1 and generate streams of MIDI continuous controller data from your analogue system. Watch out for the warranty on the ESQ, though.

Have You Met...

THE MS20 HAS two VCOs with waveforms including saw, square, variable pulse, narrow pulse, triangle and white noise. Regrettably perhaps, there is no facility for CV control of the pulse width, which makes it even less likely that you'll get thick, lush sounds from your MS20. VCO2 can be finely and coarsely detuned against VCO1, while both can be tuned over four octave settings. Ring modulation is available for metallic sounds. There are two 12dB/octave filters, one low- and one high-pass, both with resonance from zero to self-oscillating. There are two envelope generators; EG2 is the main envelope, controlling the main VCA, and is a standard ADSR affair with an extra Hold parameter, which delays the release stage after key-release. EG1 has three time controls, Delay, Attack and Release, and is most often used in conjunction with the modulation VCA for effects such as delayed vibrato, where the vibrato is not only delayed, but builds up over the attack time rather then just starting at full level once the delay time has elapsed. The modulation VCA allows some fairly clever effects to be created: it has a control input, source input and output. To create delayed vibrato, EG1 is the control input, the LFO is the source, and the VCOs are the destination. Both EGs sport reversed polarity CV outputs on the jackfield, and both of these usefully have a zero volts sustain level. This means you can apply them to the VCOs to obtain a pitch envelope without having to worry about the sustain pitch of the patch being out of tune — but watch out when you release the key.

The modulation wheel is unusual in that it isn't centre-sprung. This means that if you intend using it for pitchbends, you either have to be very careful and keep feeling for the rather weak centre click position, or you only use pitchbend in one direction, and tune the synth so that the maximum travel of the wheel in one direction gives an unbent pitch. For wheel-controlled vibrato, use the modulation VCA with wheel as the control input, LFO as the source and the VCOs as the destination.

Next to the modulation wheel is that little switch — this generates a trigger signal and holds until released. Applications for this tend towards the odd side of things. One that springs to mind is to trigger EG1, with this envelope modulating the VCOs, for an envelope-controlled pitch-sweep. This is handy for wide-ranging pitch-sweeps such as from subaudio up to the pitch of the held key. A pitchbend like this would be very tricky to execute smoothly with a wheel, especially if it occurred over a second or two. Using an envelope to modulate the pitch smoothly, some really dramatic performance effects can be obtained.

Other features include white and pink noise generators and a sample and hold module. Most people think of sample and hold as being a periodic random CV, usually sent to the filter at a rate determined by the LFO, creating a gurgling filter effect. You can do this on the MS20, but it's only one possibility. What a proper sample and hold module does is to sample the input wherever it's triggered, and hold its output CV at the discrete value obtained from the sample until the module is triggered again. The input could be noise, as is the case in most preset sample and hold modules, but it could equally be an envelope, LFO, modulation wheel or whatever. Suppose you use the LFO as a source: the MS20's LFO has two waveforms available separately and simultaneously. The LFO waveforms themselves are continuously variable In one case, you can vary the waveform from a falling sawtooth, through triangle to rising sawtooth. In the other case you can vary from a wide pulse, through square, to narrow pulse. If you're triggering the MS20 from an external source (sequencer, drum machine), then you can trigger the S&H unit on every new note of a particular sequence, and with the LFO set to a slow rising sawtooth, and the modulation destination set to the lowpass filter, the result would be sequences of notes with increasingly open filtering. Since the LFO frequency is independent of the tempo of the music, these timbral sequences would tug against the beat in a shifting manner. Fascinating to hear, easy to control and, again, the sort of thing even sophisticated algorithmic composition software and clever synthesiser programming might be hard pressed to imitate.

See You Soon...

THERE AREN'T MANY two-oscillator analogue synths you can pick up for less than a hundred quid these days — few of these will have two filters (four if you count the two in the ESP section). Still less of these two-figure bargains are also sophisticated analogue signal processors.

To me the MS20 is like a Minimoog: in a class of its own. When synths were synths and only for synth music, the MS20 wouldn't earn you hero status. But those days are gone — today the more discerning producers have tired of the search for the ultimate snare drum, and are looking for something different, something they haven't heard before. They may hear it in the MS20 — so may you.

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

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Music Technology - Jun 1989


Vintage Instruments

Gear in this article:

Synthesizer > Korg > MS20

Gear Tags:

Analog Synth

Retrospective (Gear) by Greg Truckell

Previous article in this issue:

> Front Line

Next article in this issue:

> Yamaha RX8

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