This project uses an Arduino as a digital effects processor for guitar, and is a derivative of this guitar pedal project by . This project uses the same schematic presented in the instructable, as well as the DSP library used for simulating analog output. However, I have rewritten the effects engines to provide zero-centered sound data and cleaner tones. Currently, I have implemented simple effects such as delay, a leslie-style tremolo, and a fuzz box.
To achieve a pure analog signal, the DSP files accelerate the Arduino’s PWM output by adjusting the prescalers for timers. This PWM signal is then sent through a filter capictor to smooth out the pulses. However, adjusting these prescalers also knocks out the serial connection, so debugging can be a bit tricky. Curiously, the DSP library code must be uploaded to the Arduino using an old version of the Arduino IDE (0020). I suspect this is because of advancements made in the Arduino library, but I have not yet found a way to make the DSP files compatible.
Overall, I was quite impressed with the Arduino’s performance, considering that it was not built for DSP work. Check out the code on my GitHub!