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8. Synthesis basics: Subtractive synthesis
To remedy this problem, many synthesizers have a parameter called Filter Keyboard Tracking. When this
is activated, the filter Cutoff Frequency varies with which key you play, just as the oscillator frequency
does. This ensures a constant harmonic spectrum for all keys.
Amplitude
R R R R
( ( ( (Q-
Q-
Q-
Q-
E E E E S S S S O O O O N N N N A A A A N N N N C C C C E E E E
Resonance in a filter is created by connecting the output of the filter to its input, in other words setting
up a "feedback loop". This feedback connection already exists inside the filter, and the amount of feed-
back is then controlled with a Resonance parameter on the filter module. Resonance is also referred to as
Q-value.
When you apply resonance, the frequencies just around the cutoff point of the filter will be amplified
(louder). As you increase the resonance further and further, the filter will start to behave more an more
like a bandpass filter, where only the frequencies around the cutoff point are let through. The filter will
start to "ring", which means it almost sounds like it is adding frequencies to the sound. If the resonance
is then raised even further (on some Nord Modular filter modules), the filter will start to self-oscillate,
producing a sound of its own, just like an oscillator.
The figure below shows a lowpass filter frequency spectrum at different resonance amounts (Q-values).
Amplitude
Q=1
Q=0.5
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) ) ) )
V V V V A A A A L L L L U U U U E E E E
Q=4
Q=2
Cutoff
Frequency
Frequency
Frequency
NORD MODULAR V3.0
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