You are going to face a number of tasks: 1) How to obtain your digital guitar signal. IE you need to read the A/D output from somewhere. Perhaps you have a library or set of routines already to access the data from your sound card. If you don't this is going to be step 1. 2) As the previous answerer posted this is no simple task but it can be fun to experiment. Basically for a wah effect you are looking for a variable filter. Filters can be low-pass, band-pass, high-pass and many others. The Wah effect is usually a variable filter that takes the high end (upper frequency) and as you rock the Wah pedal lowers that high end. This was the simplest form of Wah filter. They are much more complex now days. I built an analog version many years ago and it wasn't too hard. Unfortunately in the digital world it is actually a little harder to do. But once you have the data from step 1 you can write some code or use a library to modify it and get some interesting results. 3) Sending the modified data some where. Again like step one you are going to need to figure out where/how to transmit your modified data back out either to your sound card or perhaps in early stages just write it to a WAV file and then play that file back to see what your filters did. I think there are signal processing libs in MatLab as mentioned above. There are probably some commercial libs to do this as well. I unfortunately cannot point you to any. Good luck