[LAU] Wah update

Justin Smith noisesmith at gmail.com
Mon Jul 20 00:32:21 EDT 2009

On Sun, Jul 19, 2009 at 8:10 PM, Ken Restivo<ken at restivo.org> wrote:
> Just a quick update on the wah research.
> A friend owns a Dunlop "Jimi Hendrix Wah", which says it is the "Original Thomas Design", by which I assume they mean to claim it's the same design as the Thomas Organ Wah, formerly Vox.
> This website's describes the frequency response as a lowpass with a resonant peak:
> http://www.geofex.com/Article_Folders/wahpedl/wahped.htm
> So here is what JAPA says it does (and I believe JAPA more than some random website):
> When fully closed, it's a bandpass, with a VERY high Q!
> http://restivo.org/misc/lowend-jimi.png
> But, wait, when I open it up, suddenly it becomes more like a highpass, but with a lot of resonance:
> http://restivo.org/misc/midrange-jimi.png
> When it's fully opened, it's definitely a highpass, but with a helluva peak:
> http://restivo.org/misc/high-jimi.png
> So, not only is the opposite of what that article says, but it's also kind of non-linear. I'll poke around the various LADSPA plugins and see if I can find something nearly like this.
> Another guitar-player friend has a different wah (IIRC, either a "Cry Baby", or a Morley), and I'll see if I can run his through this and see what it comes up looking like.
> -ken
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Cool. Nice to see some good open source DSP design in process. Is your
goal to make something like a wah with a combination of LADSPA plugins
or would you also consider making a new plugin emulating this
behavior? It may be worth considering trying to build something in
puredata or csound, given that they have much more fine grained
control for building customized processing chains than could be done
in a single instance of jack-rack.

I think the best way to mimic the wah behavior will probably be to
manipulate the Q and center frequency based on a pair of table
lookups, or additionally/alternatively you could have a pair of
filters and crossfade between them based on your virtual pedal

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