ENSONIQ SQ-R

S&R Miisician 's Manual Section 6 - Standard Soimd Programming
Filter Bank
Each SQ-R voice has its own pair of digital filters, Filter 1 and Filter 2, which are
connected in series. The filter settings determine which ranges of frequencies will
be allowed to pass through to the output.
Low-pass/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 a high-pass
filter — it lets frequencies higher than the cutoff frequency pass and filters out
those below. In the SQ-R, Filter 1 is always a low-pass filter. Filter 2 can be
either a high-pass or low-pass filter.
Poles: Rolloff Curves
"Pole" is an engineering term which describes the steepness of a filter, or the
filter's cutoff slope. Each additional pole gives a filter a steeper rolloff curve. In
the SQ-R, the filter modes are interdependent; that is, the combined number of
poles in Filter 1 and Filter 2 is always four.
These four poles are divided between the two filters; either as 2 and 2, or as 3 and
1. A 1-pole filter will rolloff at 6 dB per octave; a 2-pole filter, 12 dB per octave;
a 3-pole filter, 18 dB per octave; and 4-pole filter, 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.
This is the frequency at which the filter begins filtering out frequencies. The filter
cutoff frequency can remain fixed over time, or it can be varied by modulating the
filter with an envelope, LFO, velocity, etc.
Filter1/Filter2
Filter Bank
Filterl= 2LoPass
Filter2= 2HiPass
Filter 1 Mode — Determines whether Filter 1 will be a 2-pole or 3-pole low-pass
filter.
■ilter2
Filter 2 Mode — Filter 2 can be configured as a 2-pole or 1-pole high-pass filter,
or a 2-pole or 1-pole low-pass filter.
These two parameters are "tied together" in that changing the value of either will
result in a corresponding change in the other.
iher Bank 6-25