LinPlug Spectral - Manual (Page 72)

Wah-Wah
The Wah-Wah effect is an amplitude-controlled bandpass filter that can be
used to produce vocal-like sounds, particularly “wah-type” sounds.
The Sensitivity control sets the degree to which the input signal's amplitude
affects the filter cutoff frequency. Lower values produce a less-pronounced
wah effect, while higher values produce stronger, more vocal-like wah
sounds.
The Cutoff control is used to set the centre frequency (in Hz) at which the
bandpass filter operates.
The Resonance control is used to set the amount of emphasis around the
cutoff frequency. Higher settings create a more pronounced peak in the
signal while lower settings produce a flatter response.
The Volume dial is primarily to adjust the level after the filter, as the Wah-
Wah can reduce volume quite a bit (or in case of heavy Resonance even
boost it).
The Attack control is used to set the response time of the filter to changes
in the input signal's amplitude. Faster Attack times mean that the wah effect
is triggered more quickly, while slower Attack times introduce a delay before
the wah effect is produced.
The Decay control is used to set the recovery time of the filter after the
input signal's amplitude has changed. Faster Decay times mean that the
wah effect returns to its default value more quickly, while slower Decay
times mean that the wah effect returns to its default value more slowly.