perjantai 12. joulukuuta 2014

Rob Hordijk's Twin Peak Filter Simulation

Rob Hordijk presented an interesting masterclass in Sines And Squares Festival 2014:

At 10:00 of this Part-2 Video Rob starts to talk about his Twin Peak Filter. It is an interesting solution for band-pass filter. You connect two low-pass filters parallel and subtract the output of the one filter from the output of the other one. This works if the gain of the both LP filters is always equal. I decided to try this with MicroModulars classic LP filters. Filters are in 12dB/Oct mode and one filter output is inverted (F2-F1) before they are summed in mixer. I defined a morph group for resonance (max resonance is limited so that the filters are just not oscillating) of the both filters and assigned a knob to control resonance. This assures that the resonance and the gain of the both filters is equal. Pictured is the test-patch of this filter and a picture that shows the different filter topologies you can get out of this patch when you alter the cutoff frequencies of the LP filters.
In dual band pass mode when you dial equal frequencies to F1 and F2 the sound disappears and there is only silence (F2-F1=0). You can get the idea of Rob's filter easily from this emulation. It doesn't sound bad ;)

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