This article is part of the series: Modular Synthesis: Core Concepts
Modules in a modular synthesizer can be thought of as strangers sitting next to each other on a train compartment in an embarrassed silence.
Creating music from a modular synthesizer is like starting a conversation on our hypothetical train compartment, by connecting modules with patch cables and making them “speak” to each other.
For any conversation to happen we need two things: the people must have something to say (like an argument), and they must speak the same language.
In modular synthesizers, the argument is your musical idea, and it is beyond the scope of this article, while the common language to make your modules communicate is the voltage.
Voltage (and Current)
A general introduction on the concept of voltage might be useful to better understand how these instruments work.
Voltage is the difference in electric potential between two points of a circuit, or, oversimplifying, «what you apply to cause currents to flow.»[1] It is measured in volts, whose symbol is V. Without any other specification, the voltage is calculated between any point of the circuit and a reference point called ground (0 V).
Electric potential brings in the concept of current, which is the actual flow of electric charge through a circuit. Electric charge is measured in coulomb (C), while the current is measured in amperes (A): 1 ampere equals to 1 coulomb of charge passing through a given point in 1 second.
Enough for the technical stuff: now it’s time to see how voltage and current turn into (electronic) music
DC and AC
There are two kinds of current, each of which implies a different kind of voltage. They are direct and alternating current, abbreviated DC and AC respectively, and we use both in modular synthesizers.
In case of direct current, our charge flows only in one direction: if the current is steady, so will do the voltage. This kind of fixed voltages are what we use, for example, to send note information to the sound source.
In case of alternate current, our charge flows back and forth in our circuit. Its alternation over time can be displayed with a waveform diagram. In case of alternate current, the voltage changes over time as well. We use this kind of varying voltages to generate, for example, waveforms that ultimately will turn into sound.
Sources:
[1] Horowitz, Paul. The Art of Electronics. Third edition. New York: Cambridge University Press, 2019, page 1, note 2.