mixxxdj/mixxx — pull request #347 by daschuer (2014-09-24 22:05:20+00:00)
Title: Filter effect

This is a replacement of the current Filter with a Bequad type.
Bequad based filters are standard on most hardware Mixer like Pioneer DMJ-250 or Xone 22.
This on features dedicated HPF and LPF knob and a Q knob in the range of -8 to 12 dB.
The rool-off is -12 dB/Oct, this is relative smooth compared to the -48 dB/Oct Butterworth type we had before. This one is also suitable to be placed on the upcoming EQ Rack.

I am planning a Moog Ladder filter as a second filter alternative with a steeper roll-off

This PR is based on the link-fix branch. It includes a revamp of the LinPotmeter with a tweak able logarithmic scale, default to -40 db = two decades. We may add a tweak option to the effect manifest in a later PR.