ALESIS FUSION
ANALOG SYNTHESIS TUTORIAL
Highpass filter
Allows high frequency harmonics to pass through but filters out lower frequency harmonics
below the cutoff frequency:
As you can see, the fundamental and
second harmonic are filtered out (and the third is
attenuated) which will result in a very thin sound.
Band Stop / Notch filter
This filter type allows lower and higher frequency harmonics to pass through but removes
harmonics in between:
Again, you can see the effect this filter type will have on the sound - the fundamental and the
first few harmonics are
preserved, some upper harmonics are removed but the upper
harmonics remain intact. In practice, the effect of this filter is quite subtle
but it can have its
uses and when the notch is moved during the course of
a note, it can sound like a mild phase
shifting effect.
Band Boost / EQ filter
This is not so much a ‘filter’ (i.e.
a device to
remove
harmonics) but more of an ‘enhancer’ as it
actually boosts certain harmonics:
In many respects, this filter
type can be used almost as a simple tone control for accentuating
certain harmonics in the basic waveform. Its effect is subtle but it does
come into its own when
its frequency control is changed during the course of a note.
As mentioned,
the most commonly used filter type is the lowpass, probably because
psychologically
it corresponds to what we are used to hearing when playing acoustic
instruments - i.e. they tend to get mellower over the course of a
note and playing harder or
softer creates a brighter or softer sound respectively. There are other filter types however.....
Sound processors / modifiers
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