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8. THE BASICS OF SUBTRACTIVE SYNTHESIS
There are many forms of synthesis available today. The most common form, subtractive
synthesis , was pioneered on the first commercial synthesizers in the 1960s and has become
a guideline for the designers of many synths that came afterward. If you learn the basics
of subtractive synthesis, you'll find yourself able to find your way around the vast majority
of synthesizers – even new ones based on digital processes like sampling, ROM playback,
wavetable scanning, and vector synthesis.
While the original KORG MS-20 (and therefore, naturally, also the KORG MS-20 V model)
has a few unique elements to its architecture, it still serves as an excellent platform for
learning the basics of how synthesizers work.
8.1. The Signal Path and its elements: VCO, VCF, VCA
When we talk about the signal path of a synthesizer, we're referring to the path that sound
takes from its moment of creation until it leaves the synthesizer to be heard. While there are
endless variations, the basic signal path looks like this:
•
First, we must create the basic waveform of the sound, with a certain harmonic
structure. We do that with an oscillator .
•
Next, we shape the tone of this waveform by altering its harmonic content over
time. We do that with a filter .
•
Finally, we shape the amplitude (loudness) of the waveform to create individual
notes. We do that with an amplifier .
In analog synthesizers like the KORG MS-20, these three elements can have their properties
changed in real time by electrical signals called control voltages . We therefore say that these
elements are voltage controlled . Let's learn about them now, one by one.
8.1.1. The Voltage Controlled Oscillator (VCO)
The VCO is where we create the initial waveform that we then sculpt to form our
synthesized sound.
The main properties of a VCO are:
The frequency, which determines the pitch that we hear. You can set the
•
frequency of the oscillator with two controllers:
•
First, we set the octave of the oscillator. On various synthesizers, it may be
named Frequency, Coarse Frequency, Octave, or (as on the MS-20) Scale. On the
MS-20, as with many early synthesizers, octaves are marked in feet.
Why would you mark octaves in feet? Because when developing synthesizers, many manufacturers
indicated octaves the same way they were indicated on electric organs, which in turn got their settings
from pipe organs: by the length of the pipes. Doubling the length would drop the pitch by one octave: 2',
4', 8', 16', etc.
Arturia - User Manual KORG MS-20 V - The Basics of Subtractive Synthesis
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