Subtractive synthesis

Subtractive synthesis is a form of audio synthesis where the timbre of a tone or signal is changed by subtracting waveforms from it. This results in a less complex signal and a different-sounding tone.

The original tone is usually generated by an audio synthesizer. The original can be a square wave[?], a pulse wave[?], saw wave or triangle wave. The wave is subsequently modified by the harmonics from the seed waveform.

Subtractive synthesis is usually (but not exclusively) associated with analogue voltage controlled synthesizers such as the moog or the minimoog. Subtractive synthesis can produce very natural changes in a recorded sound, owing to the intuitive way in which it works.

When a lowpass filter[?] is used, the high frequencies are taken out, creating a sound which sounds very smooth, with a lot of bass. If a highpass filter[?] is used, the low frequencies are taken out, making a much harsher waveform.

Example of subtractive synthesis

The following is an example of subtractive synthesis as it might occur in a simple electronic instrument. We will create an A note using common techniques.

First, we generate a 110 Hz (two octaves below middle A) square wave:
Square.ogg

We generate a triangle wave at 330 Hz, a multiple of 110 Hz:
Tri.ogg

Both these waves are enveloped using different Attack-Decay-Sustain-Release settings:
Squareenv.ogg
Trienv.ogg

The waves are added together:
Squaretri.ogg

The added waves are subjected to a low-pass filter with a cutoff frequency that changes over time:
Filtered.ogg

The flitered note is then subjected to mild distortion:
Distorted.ogg

While this example is quite electronic and artificial sounding, the same technique can be used to create more natural sounds. When low-frequency oscillators are used to vary the parameters of the synthesis over time, sounds which are very organic indeed can be produced.

Note: Due to the lossy nature of Ogg Vorbis compression, waveforms will not appear exactly square or triangular if examined with a sound editing program.

External links

• Buzz Tracker (http://www.buzzmachines.com) - A freeware electronic music program which could be used to explore this topic further.