Microprocessor All-Pass Synths

Here are some examples of synthesis work I was doing on the M4 microprocessor before my PhD Qualifying Exams happened. Most of these involve large chains of allpass filters. Click through to listen.

No post-processing was done on any of these. They were generated straight off the M4 chip, without an external ADC/DAC, (which is the next thing to research)...

Single-sample impulses pushed through 200 2nd-order allpass filters in series (with a single comb filter). The only parameter adjusted was feedback gain. running on a cortex m4 microprocessor. Sounds like a spring reverb.

Lots of cascaded allpass filters with feedback, driven with sinewaves and pulses. Some extra knob tweaking occurred on this one. 🙂

This patch I actually gigged a little with in the fall. It is a pseudorandom oscillator connected to a cascade of 800 allpass filters w/ feedback. There is delay built into the filters. I was tweaking pseudorandom generator parameters on the oscillator with LFO's, and controlling the amount of the excitation into the filters, and also tweaking filter Q, frequency, and feedback. Really fun to play! It's called "It rained, but we were sexed early."

Everything was written in C for the Cortex M4 processor. I have a standalone modular device, which is capable of running on rechargeable batteries, and surviving extremely rough conditions. For some example code, check out my GitHub.

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