Subtractive Sound Synthesis

Subtractive Synthesis

• Involves subtracting frequency components from a complex tone to produce a desired sound

• Why is it not worth trying to subtract frequencies from a sine wave?

• A sine wave only contains one frequency

Subtractive Synthesis

• Unwanted frequencies are attenuated using filters

• The most basic subtractive synth needs at least one oscillator and one filter

Subtractive Synthesisers

• Subtractive synths provide:

• two or more oscillators

• a noise generator

• at least one filter

• at least one envelope

• an LFO

• a modulation matrix

Filters

• Used to attenuate spectral components

• Implemented using electronic components or a digital algorithm

Filter Types

• Low Pass Filters

• High Pass Filters

• Band Stop Filters

• Band Pass Filters

Low Pass Filter

Amp.

Cut-off frequency

Frequency

• Lets through everything below a certain frequency

Filter Slope

• Ideal filters are like brick walls

• All real filters have slopes

• So some sound gets through beyond the cut-off

Filter Slope

KHz

dB

500 8000

roll-off

A low pass filter with a gentle slope of 6dB per octave.

High Pass Filter

Amp.

Cut-off frequency

Frequency

Band Pass Filter

Amp.

Centre frequency

Frequency

Band Stop Filter

Amp.

Centre frequency

Frequency

Envelopes

• Determine how the value of a certain parameter of a sound changes over time

• Can be used to alter any parameter, e.g. pitch

Amplitude Envelopes

• How the amplitude varies over time affects the character of a sound significantly

• So most synthesisers have an amplitude envelope

time

amplitude

attack decay sustain release

Amplitude Env. Parameters• attack – occurs at the start of the wave and is the

time it takes for the sound to reach peak amplitude

• decay – the time it takes for the peak amplitude to fall back (possibly to zero)

• sustain – the amplitude level the sound will fall back to following the initial decay

• release – the amount of time it takes for the sound to fall back (or decay) to zero after the sustain period (or after the key is released)

TS404 AMP ENVSubtractor

AMP ENV

Modulation

• Modulation traditionally means to change the key of a piece of music

• With synths it means to alter a parameter (target) in accordance with another signal (source)

• Example targets: amplitude, pitch, cut-off

Modulation

• Example sources: envelope, LFO, velocity

• Alter the intensity of the modulation over time

• Slider often used to alter the max extent of the modulation (the intensity of the overall effect)

Hardwired Modulations

• The ESP allows the LFO to be applied to:

• frequency (pitch) of oscillators; or

• the cut-off frequency

L.F.O.

• Low Frequency Oscillator

• 0.1 – 20Hz

• Can be synched to the project tempo

LFOs

Modulation Matrix

• Target: parameter to be altered

• Source: signal that is used to alter target

• Slider: sets modulation intensity

• Via: varies modulation intensity by another parameter

The ES2 Modulation Matrix