12. Synthesis basics: The filter
NORD MODULAR G2 V1.1
Page 210
In the Nord Modular G2, the Nord Filter filter can be switched between 12 and 24dB modes. For sounds
with high resonance (see below), similar to those in the Roland TB-303, we recommend the 12dB vari-
ation. For most other sounds we recommend 24dB.
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The most important parameter for a filter is its
cutoff frequency
, which is the setting that determines
where
in the frequency material it should start cutting. If the cutoff frequency in a low pass filter is set to a very
low value, only the lowest harmonics (the bass) will pass through. If you raise the cutoff all the way up,
all
frequencies will be let through, as the figure below illustrates.
Changing the cutoff frequency is often referred to as “sweeping the filter”. This is probably one of the
most important ways of shaping the timbre of a synthesizer sound. By using an envelope you can for ex-
ample have a high cutoff at the beginning of a sound which is then gradually lowered (the filter “closes”
as the sound decays). This would emulate the way most plucked string sound (piano, guitar etc.) behave;
the amplitude of the harmonics decreases as the sound decays.
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When you play different pitches, the oscillators produce different frequencies. This means that the over-
tones in the waveform appear at different frequencies. The cutoff frequency of the
filter
however, is fixed.
This means that different overtones will be cut off at different pitches. To be more precise, the further up
the keyboard you play, the muddier the sound will be.
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.
