auto-wah LADSPA plugin

 This LADSPA plugin is the combination of a 'wah' pedal and
 a simple envelope follower.
 .
 Controls are:
  - Freq: the resonance frequency of wah filter.
    This would normally be controlled using a
    midi pedal.
  - Mix: crossfades between dry and wet signal, the
    first is the original input signal and the latter
    is the pure output of the resonant filter amplified
    by 18 dB.
 .
 The three remaining parameters control the envelope
 follower. This produces a control signal that is
 added to the 'Freq' setting.
  - Drive: input gain to the envelope follower (so
    this gain is not in the signal path).
  - Decay: controls the decay time of the envelope.
  - Range: controls how much the envelope is allowed
    to modify the basic frequency.