i just finished an arduino sketch that allows decent audio processing with just a few resistors and capacitors. the arduino sketch is up here:
it takes in audio on ADC0 and uses a dual pwm to create 16b audio out. you can process the audio in-between and make a low-fi effects pedal. it can be used for just analog out as well, and is much higher quality than using analogwrite (although more complicated too).
there is a much more in-depth tutorial on pwm in general up here: