On Sun, Jul 19, 2009 at 10:33 PM, Justin Smith<noisesmith@xxxxxxxxx> wrote: > On Sun, Jul 19, 2009 at 10:24 PM, Ken Restivo<ken@xxxxxxxxxxx> wrote: >> On Sun, Jul 19, 2009 at 09:32:21PM -0700, Justin Smith wrote: >>> On Sun, Jul 19, 2009 at 8:10 PM, Ken Restivo<ken@xxxxxxxxxxx> 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. >>> > >>> >>> 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'm either going to find a LADSPA plugin which does this, or hack something together in JACK-RACK or via some custom C using existing plugins. >> >> I haven't the maths skills to write any serious DSP in C, and probably not in PD or Csound either. Whatever I end up with will have to be in C, however, and efficient too, so it can run on a netbook along with many other synths and plugins. >> >>> 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 betwengn them based on your virtual pedal >>> position. >> >> Tonight I tried every LADSPA bandpass filter I could find, and none came even close AFAICT. Comparing its shape to those of other LADSPA plugins indicates to me that the "Thomas Organ" wah circuit isn't a band-pass after all, just a high-pass with a VERY high Q. So, yeah, I might be able to get pretty close with one ofthe existing LADSPA HPF's and varying the Q, as you suggested. >> >> -ken >> > > Just to clarify, the pd or csound solution would only have to have > premade filters in it, plus some parameter routing, the issue with > jack-rack is that you cannot tie parameters to one another in > jack-rack itself (and as far as I know you cannot even have parallel > signal paths), and any external solution you hack together is going to > be less efficient and more fragile than pd, csound, or the like. When > you say whatever you make would have to be written in c I hope you > understand that pd and csound are written and c and will have less > overhead than jack-rack plus whatever midi preprocessing and shell > scripting you need for the alternative approach (though I will not > argue the fact that coding the whole thing in c would be even more > efficient, but also more time consuming and error prone than a > dedicated DSP language). > > Suddenly it occurs to me that maybe your goal is to get me so > opinionated about the right way to do this that I just do it for you > myself :) > Never mind, I replied too soon, reading what you wrote more carefully, I think what I said was mostly moot. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
