Subtractive synthesis (idea)

Substractive synthesis is the sound synthesis technique you find in most analog synths, and in their digital imitations. It is a very intuitive technique for a sound designer because the synthesis parameters produce direct, natural effects on the sound.

The idea is to take an initial waveform and sculpt its spectrum with filters. It is best to start with an oscillator like a sawtooth, a pulse or any other waveform rich in harmonics, which you will modify with the shape of the filter.

With a lopass filter, you remove the high frequencies, emphasizing the basses, and smoothing the waveform.

With a hipass filter, you remove the low frequencies, emphasizing the highs, and making the waveform harsher.

Since the filters have to be effective, filters with steep slopes around the cut-off frequency work best. It is also nice to be able to set the resonance of the filter, which is a region near the cutoff where the frequencies are emphasized just before being suppressed:

• it gives a certain 'edge' to the sound when sweeping the cut-off frequency.
• it is also good for modeling realistic sounds, since most natural devices have resonant frequencies.