Korg MS-20 - features and functions

5) Features and Functions ^

Voltage Controlled Oscillator (VCO)

Frequency Modulation controls

Voltage Controlled High-Pass Filter (VCHPF)

Voltage Controlled Low-Pass Filter (VCLPF)

Cut-off Frequency Modulation Controls

Voltage Controlled Amplifier (VCA)

Envelope Generator 1

Envelope Generator 2

Modulation Generator

Manual Controllers

Patching panel
- input and output jacks
- modulation voltage controlled amplifier (MVCA)
- noise generators
- sample and hold

External Signal Processor

[Ringed numbers refer to the front panel illustration]

Voltage Controlled Oscillator (VCO) ^

The VCO is the source of all sound for the MS-20 synthesizer.
It is here that all pitch and basic tone color elements are determined. The MS-20 is equipped with two wide-range VCO's.

	Scale: This control is an Octave selector. With each halving of the number displayed, the pitch goes up one octave. For example the 4' (foot) scale indication is one octave higher than the 8'; similarly, 16' is one octave lower that 8'. VCO-1 is variable from 32' to 4'; VCO-2 is variable from 16' to 2'.
	Waveform: This selects the various waveforms that determine the basic tone color (timbre). VCO-1 has four waveforms: , , , ; VCO-2 has three waveforms: , , , plus a Ring Modulator setting. Each waveform has its own unique characteristic sound.

(Triangle Wave): A very basic waveform having few harmonics, and possessing a soft, rounded tone color. Excellent for flute, vibes and other such effects. The Triangle Wave may be changed into a Sine Wave (having no harmonics) by the use of the Low Pass Filter.

(Sawtooth): A waveform rich in all the harmonics, and one of the most useful to the synthesist. Used for string, brass, voice and other harmonically rich sounds. The Voltage Controlled Filter (VCF) is highly effective on Sawtooth Waveforms.

(Rectangle Wave): A variable waveform having different timbres depending on the width of the top (called Pulse Width). When the top and bottom widths are equal, the waveform is called a Square Wave, and possesses the "hollow" qualities of the reed family (i.e., the clarinet). As the pulse width proportionately decreases, a strong shift in tone color occurs; the sound becomes "nasal" in quality. This waveform is called a Pulse Wave. Pulse Width is varied on the MS-20 using the PW control (see below).

(White Noise): An unpitched sound consisting of equal amounts of all frequencies. Used for wind, surf, gunshot, percussion instrument and other such effects. The use of filters will emphasize certain frequencies over others, creating many different sound effects.

(Square Wave): A variation on the Rectangle Wave, with equal top and bottom widths. A "hollow" sounding waveform with only odd numbered harmonics present. Used to simulate reed instruments and other closed pipe sounds.

(Pulse Wave): This Rectangle Waveform has a relatively narrow top width, and is characterized by a "nasal" tone quality, with strong presence of upper harmonics. Used to simulate double reed instruments (e.g., the oboe) and certain plucked string sounds (e.g., harpsichord and clavinet).

(RING) Ring Modulator: This setting combines the sounds of both VCO's in such a way as to create sums and differences of all harmonics present. The result is a clangorous, "metallic" sound which is useful for gong, chime and other such effects. The two Scale controls as well as the Pitch and PW controls all affect the resulting sound, and should be used judiciously to create the desired effect.

[vco waveforms]
- VCO waveforms

	Pitch: This control varies the VCO-2's pitch over a range of +/- one octave. You can either match VCO-2's pitch to VCO-1, or set it at any relative interval (e.g., third, fifth, etc.) Once set, the pitch level remains extremely stable throughout the playing range, thanks to Korg technology.
	PW: This control varies the pulse width (PW) of VCO-1's Rectangle Wave. At "0", the waveform is symmetrical (i.e., a Square Wave). Rotating the control clockwise proportionately decreases the pulse width. Near the full clockwise position, the pulse width becomes so narrow as to virtually disappear, and no sound will be heard.
	Portamento: Varies the rate of "glide". . .the time it takes the MS-20 to go from note to note. The ability to effect smooth transitions in pitch between notes is unique to the monophonic synthesizer, and adds to the creative effects available.
	Master Tune: This control varies the pitch of both VCO's over a range of +-2 semitones, so that you can match the synthesizer's pitch with that of other instruments.

Frequency Modulation controls ^

These controls allow other parts of the synthesizer to affect the VCO's pitch, for such effects as vibrato, trills, pitch bends, "sweeps," etc.

	MG / T.EXT Varies the intensity of vibrato from the Modulation Generator (MG) Triangle Wave output, or whatever signal is patched into the TOTAL jack.
	EG1 / EXT: With no patch in the patch panel's FREQ jack, this control varies the effect of the Envelope Generator 1 on the VCO's. Advance the control and play a note on the keyboard. Notice that the pitch of the note rises and falls corresponding to the envelope curve (see Envelope Generator 1). With any external controller patched in (e.g., Control Wheel, Reverse Envelope, etc.), the control now varies the intensity of this effect.
	VCO Mixer: Independent output level controls for VCO-1 and VCO-2 allow the user to freely adjust the balance of the two oscillators, or eliminate both VCO's when processing external sound sources.

Voltage Controlled High-Pass Filter (VCHPF) ^

This removes portions of the harmonic elements present in the waveform chosen with the VCO section. The cut-off frequency is variable from the low range on up. Use the Cut-Off Frequency knob or an external control voltage to determine the cut-off frequency.

Cut-off Frequency: The scale on this knob goes from 0 ~ 10 but in the "0" position, the filter is completely open and the basic tone color of the waveform is left unchanged. As you turn up the knob, the tone color becomes brighter. Play a note on the keyboard, turn the knob, and note the effect.

Peak: This knob determines the amount of amount of emphasis applied to the area right before the low-range cut-off frequency chosen with the knob above. When turned up to around its maximum position, the filter itself begins to oscillate, becoming in effect another sound source. This self-oscillation capability is another big feature found in the MS-20.

Voltage Controlled Low-Pass Filter (VCLPF) ^

This removes upper harmonic elements of the waveform chosen with the VCO section. The cut-off frequency is variable from the high range down, and is adjusted by means of the Cut-Off Frequency knob or an external control voltage.

Cut-off Frequency: The scale on this knob goes from 0 ~ 10 but in the "10" position, the filter is completely open and has no effect on tone color. As you turn up the knob counter clockwise, the sound will gradually become more rounded. At the lowest setting it becomes barely recognisable as a sound. Turn the knob while playing a key, and note the effect.

Peak: This knob emphasises the point right before the cut-off frequency. Near its highest position, the filter itself begins to oscillate. This self-oscillation may be used as a separate sound source.

Cut-off Frequency Modulation Controls ^

These controls allow other parts of the synthesizer to vary each filter's cut-off frequency, in a manner similar to VCO frequency modulation.

	MG / T.EXT: The Modulation Generator's Triangle Wave output modulates the filter frequency, for filter vibrato, automatic "wa-wa", etc.
	EG2 / EXT: This control varies the modulation intensity from Envelope Generator 2 (when no patch is in the respective filter "CUT OFF FREQ" jack). This highly useful effect is called "filter contouring", and allows you to obtain changes in tonal quality over time. Learn to use this function, and to experiment with different settings of Envelope Generator 2 controls. When an external device (e.g., Control Wheel, Pedal, Reverse Envelope, etc.) is patched into the appropriate filter CUT OFF FREQ jack on the patch panel, this control varies the intensity of the external modulation effect. - high pass filter / low pass filter
	Voltage Controlled Amplifier (VCA): This device varies the volume of sound passing through it in accordance with the sum of control voltages from Envelope Generator 2 (EG 2), and from any external controller patched into the patch panel VCA INITIAL GAIN jack.

Envelope Generator 1 (EG-1) ^

A special purpose Envelope Generator which is internally patched to the MS-20's VCO's and MVCA (Modulation VCA) control inputs for pitch bends and delayed vibrato effects respectively. In addition, both normal and reverse envelopes are available at the patch panel for greater flexibility.

	Delay Time: Determines the amount of time between the arrival of the trigger signal and the beginning of the attack cycle.
	Attack Time: Adjusts the time it takes for the Envelope voltage to go from zero to its peak level following the end of the delay time.
	Release Time: Determines the amount of time it takes for the voltage to drop to zero again following the termination of the trigger signal.
	- envelope generator 1

Envelope Generator 2 (EG-2) ^

This device generates a rising and falling voltage which when applied to the VCA and VCF produces corresponding changes in volume and tone color respectively. The MS-20 features a unique 5 part Envelope Generator for added flexibility. When "triggered" (usually by depressing a note on the keyboard), the EG voltage rises to a peak at a rate set by the Attack Time control, then falls at the Decay Time, control rate to a level set by the Sustain Level control, and eventually falls back to zero following termination of the trigger signal and the end of the hold Time at the Release Time control rate.

	Hold Time: Extends the trigger signal by a variable amount of time. In effect, it "remembers" the trigger for a specified time period.
	Attack Time: Sets the time the voltage takes to rise to a peak.
	Decay Time: Sets the time the voltage takes to fall from the peak to the Sustain Level.
	Sustain Level: Sets the voltage level which will be sustained for the duration of the trigger signal (plus time set by Hold control).
	Release Time: Sets the time the voltage takes to fall to zero following termination of the trigger signal.

The EG-2 output is internally patched to the VCA so that changes in volume over time will occur to sounds according to the EG-2 control settings. In addition, another EG-2 output is sent to the Filter Modulation controls (EG-2/EXT) so as to modulate the VCF's cut-off frequency. In this mode the filter's "steady state" is the Sustain Level. The filter's cut-off frequency will start below this level initially, will rise above the Sustain level during Attack cycle, will fall to the Sustain level, and then will fall below to the initial level again following trigger release.

- envelope generator 2

Modulation Generator (MG): ^

This device generates a variable speed low frequency modulation signal, and is also known as a Low Frequency Oscillator (LFO). Its main purpose is to provide vibrato, trills, repetitive attack, and other cyclical (i.e., repeating) types of modulations.

The MS-20 MG features two different simultaneous waveforms- triangle and rectangle- both of whose shapes are continously variable by means of the Waveform control (see front panel diagram). The MG frequency is selected by the Frequency control, and is displayed via a flashing red LED for easy visual confirmation. Both waveforms are available via patch panel connection. In addition, The MG's Triangle Wave is internally patched to the VCO's and VCF's via their respective MG Modulation Intensity controls. This modulating signal is patched through the T.EXT jack on the patch panel.

A different modulation signal (e.g. Sample & Hold, "Delayed" Vibrato, Wheel- controlled Vibrato, etc.) may be substituted at any time and routed to all three MG intensity controls via this input jack.

- modulation generator waveforms

Manual Controllers ^

Consists of two Controllers located to the left of the keyboard for easy manipulation while playing.

Programmable Control Wheel:

When connected to various control inputs, this highly useful device can give such effects as pitch bends, modulation depth control, filter "sweeping", sample and hold "arpeggios", and many more.

Momentary Switch:

This switch is useful for triggering either or both MS-20 envelope generators, or for triggering external devices, i.e., another synthesizer or sequencer.

Patch Panel ^

External Signal Processor (ESP): ^

This powerful module allows external instruments to actually "play" the MS-20 synthesizer, with the same power and flexibility as achieved by playing the keyboard!

Since everything in a synthesizer is voltage controlled, it is normally not possible to control a synthesizer directly with an external instrument, which generates audio signals. However, the MS-20's ESP module permits external sound sources to vary the synthesizer's pitch, volume, tone color and attack and decay by means of built-in Pitch and Envelope Followers, which produces control voltages conforming with the input signal's pitch and volume respectively. A trigger signal can also be produced to trigger the MS-20's Envelope Generators, for programmed attack/decay cycles.

The ESP module consists of high gain preamplifier, variable band-pass filter, Envelope Follower/Trigger Detector, and Pitch to Voltage converter. The various outputs are available at the patch panel for connections to other parts of the synthesizer.

[See the MS-20 synthesizer E.S.P. owners manual supplement]

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