This term is normally used to refer to the tradional synthesis model used by analog synthesizers in the 1970s. It is also known as subtractive synthesis. It involves oscillators, the outputs of which are mixed together and fed into a filter (where certain frequencies are subtracted) after which they are fed through an amplifier. The amplifier and filter are normally also driven by envelope generators....
Korg MS-20
"The MS-20 [the most popular of the MS series] was designed in Japan by Messrs.
Mieda (who designed Korg's first keyboard product, and organ back in 1967 and went
on to become head of Korg engineering) and Mori (who moved on to a special
engineering group working working on new synthesis techniques, after leading the
design teams on the CX-3, Mono/Poly and Poly 800). The idea behind the MS-20 was
to produce a scaled down version of Korg's bulky PS series of polyphonic patch bay
synths produced in the same year. At this time, there were plenty of good small mono
synths on the market, but few boasting patch bays like you'd find on the big boys from
Moog, Moog, or indeed Korg. (The beauty of a patch bay is that you can physically
connect 'modules' of the instrument, such as the filter, the oscillator or the LFO, in the
precise way you want rather than having to stick to a predefined layout and routing.)
"The MS-20 stands out physically, with its steeply sloping control panel (though it
doesn't collapse like that of the Minimoog) and tiny, 'professional-looking' schematics
and labels dotted about on its battleship-gray metal casing [with a 3-octave 37-note (C-
C) keyboard and 35-socket patch bay]. High-quality components were used; the control
knobs [a total of 36] offer the sort of precision that only money can buy. Compact
compared to the PS series, the MS-20 is still an awkward shape, with the lone control
wheel tucked down below the botttom C on the final inch's worth of ledge. The design
has definite pose value, but once cased, an MS-20 does make a hefty package to cart
around.
"This is a dual-oscillator synth. Each Voltage Controlled Oscillator, or VCO, has its own
marked-out area of panel, allowing you to set up different waveforms and different
pitches for each. VCO1 offers triangle, sawtooth and variable-pulse waveforms, as well
as white noise (for steam sounds, explosions, breath of wind sounds, etc.). Pitch can be
varied over four octaves. VCO2 offers sawtooth, set [non-variable] square and narrow
pulse waveforms, and a ring modulator. The ring modulator setting harnesses both
oscillators to produce those hard-edged bell and gong-like sounds used in the 1990s by
artists like The Shamen. VCO2 is also scaled one octave higher. To the right, there is a
small mixing panel with separate control knobs for VCO1 and VCO2 levels. Pitch can be
modulated by the LFO or one of the two envelope generators.
"Already this has the makings of a powerful system: independent waveforms, ring
modulation, noise, independent balance. But the MS-20 also offers separate low- and
high-pass filtering, each with its own 'peak' (resonance) controls. Filtering can be
modulated by the modulation generator (LFO) for filter vibrato or wah effects and
shaped over time using one of the envelope generators.
"The modulation generator itself offers a number of knob-controlled waveshapes, plus
full control over mod speed. There are two envelope generators [which can be triggered
via the keyboard or a manual trigger button]: EG1, which is internally routed to the
oscillator, featuring delay [to delay the triggering of the envelope], attack and release
time; EG2, which is generally used for shaping both VCA and VCF and offers attack,
decay, sustain, release and hold. [Both envelopes are available in the patch bay at
positive and negative values.]
"Along with Portamento (a lone knob governing time - i.e., speed) and master tune,
these are the MS-20's basic sound-generating tools. Features under know control are
simple and direct. If you want to carry out more advanced maneuvers, then you can reel
out sundry lengths of spaghetti and start customizing and patching. You can, for
instance, reverse the polarity of the EGs; patch in a footpedal to control the filter cutoff
in real time; make use of a sample and hold circuit (for crazy, random squeaks and
squaks); or harness the (darker) pink noise, either as a source or a modulation signal.
"You can also get really adventurous and use the MS-20's own pitch-to-voltage
converter and External Signal Processor inputs to trigger the instrument from a guitar or
even a microphone, for a form of guitar synthesis or vocoding. You can also fire off an
MS-20 sound triggered from, say, a snare drum on tape. The flexibility this offers, both
internally and externally, is almost unlimited -- providing you have the time, the
inclination and a modicum of knowledge to exploit it. If you are lucky enough to find one,
the MS-20 manual is extremely concise and helpful on the subject of patching."
"What does an MS-20 sound like? The 12dB/octave filtering (using custom-designed
Korg filters) may not furnish the raw power of a Curtis chip, but the high/low (and even
bandpass, from the patchbay) filtering options, plus ring modulation, definitely give the
instrument bags of character, in the hard-edged, electronic way that is totally in keeping
with its vaguely military appearance. In pure sound terms, Korg Japan advises that the
signal-to-noise ration does leave a little to be desired, so you might want to gate out
residual white noise inherent in the circuitry. the problem may be particularly apparent
on the MS-20's single-oscillator baby brother, the MS-10, whose white noise generator
delivers a sound more like breakup than noise anyway.
"A point of interest is that Korg UK's Phil MacDonald sampled his own MS-20 for many
of the 'spitty' drum noises on Korg's i-series workstations. Phil's [MS-20] is one of the
extremely rare 'Big MS-20,' giant-scale versions of the instrument made by hand for a
select number of star endorsees [including Keith Emerson, YMO and Kitaro] and music
colleges. Only around 20 of these instruments were ever produced."
"Though relatively reliable, the MS-20 can use standard transistors and op amps,
rendering spares not a problem, theoretically. When examining a second-hand unit, it
might be advisable to check the state of the jack field (sockets can rust, among other
things), though even these can be replaced without too much heartache. A number of
accessories were produced, including cut-to-length patchcords [only two were provided
when you bought the MS-20 new]; the MS-01 foot controller, with which you can
operate parameters like filter cutoff in real time; and the SQ-10 analog sequencer, which
allows you to program a sequence of up to 24 notes with individual pitch, timing and
tone color. (Since the unit can also be used to store MS-20 sounds, it makes a useful
addition to your system.)
"Interfacing the MS-20 with the outside world was always a bit of a problem, largely
because Korg adopted the Hz-to-voltage system rather than the more common on volt-
per-octave standard used by the other synths at the time. Korg's stout devense was the
Hz-to-voltage gives you greater oscillator (pitch) stability. Track down an MS-20
interface, which converts to one volt-per-octave, or more likely a third-party equivalent, if
you feel the burning need to interface with other synths and sequencers."