The Itti Bitti uses the PIC's built-in A/D converter to sample audio signals, and then it uses a really crude D/A converter made with resistors to send the sound out. Current it just passes the audio through itself, but it could do more! The sound is sampled and played back in 8 bits.
How it Works
There is a very simple software loop that gets a sample from the A/D and copies it to the DAC. The loop runs on a timer so that the sample rate can be adjusted. You can adjust the sample rate using a pot connected to one of the PIC's analog inputs. This lets you control the sample rate from that of noisy but intelligible all the way down to totally awful but radical! Some simple modifications to the code will allow different sample rates to be used, although at the highest setting it's pretty much going as fast as possible. Some of the timing requirements of the A/D are being ignored, but from my testing in another application, it doesn't seem to make any difference.
There is no anti-aliasing filter, so frequencies above the Nyquist rate (which can be incredible low!) get folded over to create all sorts of weird sounds that were never intended to be there. This is quite apparent at very low sample rates. Some very low rates create sounds that bring me back to the 80s and sound like audio sampled on the C64! Inputting a sweeping tone and adjusting the sample rate produces all kinds of strange and interesting sounds. I'm sure guitar or bass sounds would be mangled to complete awesomeness!
http://www.andrewkilpatrick.org/mind/itti_bitti/
