Subtractive synthesis

Considered the baseline of synthesis, subtractive synthesis is a great foundation for your understanding of differing types

We’re going to begin by looking at the most common form of synthesis, known as subtractive synthesis. In some circles, you may hear subtractive described as analogue synthesis; it is effectively the same thing, but in the case of the latter, the moniker has stuck thanks to subtractive’s association with analogue synthesisers – very much those existing in the hardware world, rather than software. Analogue technology with subtractive synthesis was where it all started, with many of the current crop of synth plugins looking to emulate the early vintage classics. Like most audio-related matters, subtractive works on a principal of a signal chain, so we’ll begin at the front of this chain, with the oscillator.

In literal terms, the oscillator emits a pulse a number of times per second. The more frequent that these pulses become, the closer together they are, with the consequence being that as they increase in frequency, the sound moves from a singular pulse to something which sounds like a pitch.

The frequency of these pulses is measured in a unit known as Hertz, which literally translates as ‘cycles per second’. Even if you’re not great at mathematics, it’s a relatively simple concept. Let’s take a common note, such as the note A, above middle C. This is often used by guitarists to tune, and even used by full symphony orchestras. It’s also referred to as A440 as the 440 is its measurement in Hertz, being 440 pulses per second. If you drop that note by one octave, the rate divides by two, becoming A220. Drop another octave and it becomes A110. Keep on like that and you will eventually reach A27.5, which starts to become less of a note, and more of a series of pulses. And just in case you’re wondering, yes you do double the figure every time you go an octave higher.

So now you’re probably thinking, ‘well, that’s all very well, but what’s it got to do with my synth sound?’. The word frequency appears a lot in discussion of synthesis, and in this setting the frequency of a note translates to how many pulses there are per second, which also translates to the pitch of the note. Save that frequency thought; we shall return!