Retrobilly tries to output some 16000hz wave files.

Quote from PoorAussie:

I spent a few hours tonight putting together a small (no pun intended) ROM which tries to output some 16000hz wave files. It works fairly well, except for some “noise” I am finding hard to get rid of, likely related to the non linear distribution of the SMS channels. . It uses two square channels and some preprocessing to get it into a SMS format that is adequate. 3 Squares might help get rid of some of the noise, but I found that small delays between each square channel adds its own distortions.

Scott from SMS Power Radio did the intro for it.

http://www.smspower.org/forums/viewtopic.php?t=11940