I ask this mostly because I want to understand what sort of output signal I= need like if I wanted to make a subtractive synthesizer. Is the square wa= ve that comes out of a 555 something that can be used, then filtered to mak= e different sounds? Kind regards, Lindy --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .