[sdiy] Pole Mixing

Brian Willoughby brianw at audiobanshee.com
Fri Apr 9 19:53:49 CEST 2021

This is excellent! Thank you for sharing this online.

As a Matrix-12 owner, I appreciate the list of presets that cover the available modes. It looks like you've even included some modes that aren't available in the Oberheim. Is that correct?

Did you use impulse response measurements to obtain the frequency response?

The reason I ask is that I wrote a macOS CoreAudio application that can load various AudioUnit plugins and measure their frequency response by simply feeding a short, 1-sample impulse into the plugin and doing a Fourier transform on the result. This only works for pure LTI (Linear Time-Invariant) plugins, but it's spot-on for those that fall into the category (i.e. no distortion or envelope-controlled dynamics).


On Apr 8, 2021, at 15:24, David Moylan wrote:
> Hi All.  I banged together a little web app to play around with filter pole mixing, of the Oberheim Xpander type.  You can mix poles in varying amounts and see the output magnitude shape as well as the transfer function.  Y axis is Db and X axis is log scale based on normalized frequency (so basically 1 equals the cutoff frequency).  Haven't done phase plot yet.
> If you have an interest in this sort of thing check it out:
> https://expeditionelectronics.com/Diy/Polemixing

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