Peterson Sonuus Wahoo - Manual (Page 16)

16 © Copyright 2012 Sonuus Limited Wahoo
Owner’s Manual
Note that frequencies above the cutoff frequency do not immediately fall to zero. The slope of the
curve beyond the cutoff frequency is called the filter roll-off and is a characteristic of the filter. The
roll-off is measured in dB per octave and the low-pass filter in the Wahoo has a roll-off of 24dB per
octave. The band-pass filter has a roll-off of 12dB per octave on each side of fc. Note that this means
the low-pass filter is more effective at removing frequencies above fc than the band-pass filter.
The shape of the filter around the cutoff frequency is another characteristic of the filter and is
represented by the parameter Q (or resonance). A high value of Q is associated with a “peaky” filter
which has high gain at the cutoff frequency. At maximum Q the Wahoo filters will self-oscillate at fc
even with no input signal.
Unlike other filter effects, the Wahoo lets you dynamically change the filter Q as the cutoff frequency
changes by using the
Q-hi and Q-lo parameters. This gives you enhanced control of the sonic
character of the filter and makes it easier to emulate vintage filter effects.
Different effects are achieved using low-pass and band-pass filtering. Low-pass filtering will retain
more of the original signal’s low end, whereas band-pass filtering can often introduce more character
into the sound.
FILTER
curve. Changing the curve lets you adjust the “feel” of the footpedal, or the response of the
envelope tracker. Take the example of using the footpedal to control the cutoff frequency of the filter.
Normally the filter cutoff, from
freq-lo to freq-hi, is mapped linearly to the output via the position of
the footpedal. The minimum filter cutoff is usually achieved with the footpedal in heel down position
and the maximum with the footpedal in toe down position. The filter cutoff is controlled linearly by
the position of the footpedal when the footpedal is between its two extreme positions.
The Wahoo allows you to change this mapping from linear to the curves shown below.
-20
-10
0
10
20
30
40
50
Frequency
S
ig
nal
Le
ve
l [
dB
] low-Q
mid-Q
high-Q