External Signal Processor - Arturia KORG MS-20 V User Manual

5.6. External Signal Processor

The External Signal Processor (ESP) is a processing chain for external audio signals. Fumio
Mieda, lead designer of the original MS-20, thought it might be fun for guitarists or other
musicians to run signals through the MS-20 architecture, as well as actually play the MS-20
from their instrument.
To do this, the signal from the instrument is input to the ESP (SIGNAL IN), run through an
Amplifier to get a good volume for future processing (Signal Level), then routed through a
Bandpass Filter to remove extreme low (Low Cut Freq) and high (High Cut Freq) frequencies
that could adversely affect the later elements in the chain. Note that the audio signal can be
tapped after the Amplifier or Bandpass Filter with the appropriate OUT patch points.
The next module is the Frequency-to-Voltage (F-V) Converter. This analyzes the frequency
of the incoming signal and creates a control voltage from it that tracks the pitch of the
instrument. The output is provided at the F-V CV OUT patch point. The actual voltage that's
output from there is fine-tuned with the CV Adjust knob. That provides the pitch information
the synthesizer needs.
To control the synth pitch, you can plug F-V CV OUT to VCO 1+2 CV IN.
To start and stop notes (and provide a semblance of dynamics and envelope shape), the
original signal from the Amplifier is split and routed to an Envelope Follower, which creates
a voltage based on the loudness it sees at its input (ENV OUT). In addition, when the signal
input reaches a level determined by the Threshold Level knob, it sends a TRIG OUT to start
the note playing.
In practice, the ESP requires a great deal of careful playing and pitch stability, but it can
produce some truly fun results – and you don't even need an external instrument to use it!
It's perfectly happy listening to signals from elsewhere in the synth and processing them.
Experiment!
75 Arturia - User Manual KORG MS-20 V - The Hardware Panel