Section 7 — Voice Parameters
EPS-16 PLUS Musician's Manual
About Filters
Each voice of the EPS-16 PLUS' twenty voices has its own pair of digital filters,
F1 and F2, which are connected in series. The filter settings determine which
frequencies will be allowed to pass through to the output,
Low-Pass and High Pass
A low-pass filter allows only those frequencies below the filter cutoff frequency
to pass—higher frequencies are filtered out. The reverse is true for the high-pass
filters. In the EPS-16 PLUS, the first filter (F1) is always a low-pass filter. The
second filter (F2) can be either a high-pass or low-pass filter.
Poles: Rolloff Curves
"Pole" is an engineering term that describes the steepness of a filter. Each
additional pole gives a filter a steeper rolloff curve. In the EPS-16 PLUS, four
poles are available, but they are divided between two filters; either as 2 and 2, or
as 3 and 1. A single-pole filter will rolloff at 6 dB per octave; a 2- pole, 12 dB
per octave; a 3-pole, 18 dB per octave; and 4-pole, 24 dB per octave. To
reproduce a 4-pole low-pass filter (for that "classic" analog synth sound) you
would set both low-pass filters to roll off at 12 dB per octave, resulting in a 24
dB per octave rolloff.
Cutoff Frequency
Every filter has a "knee" in the response curve, known as the cutoff frequency.
The filter cutoff frequency can remain fixed over time, or it can be varied by
modulating the filter with an envelope, LFO, velocity, etc. You can create some
very interesting filter configurations by using a different modulator for each filter.
For instance, try using pressure to modulate the filter. You can drive one filter up
with pressure, while simultaneously driving the other down.
7 - 20
About Filters
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