Real time pitch detection

I found several open source implementations of real-time pitch tracking

• dywapitchtrack uses a wavelet-based algorithm

• "Realtime C# Pitch Tracker" uses a modified autocorrelation approach now removed from Codeplex - try searching on GitHub

• aubio (mentioned by piem; several algorithms are available)

There are also some pitch trackers out there which might not be designed for real-time, but may be usable that way for all I know, and could also be useful as a reference to compare your real-time tracker to:

• Praat is an open source package sometimes used for pitch extraction by linguists and you can find the algorithm documented at http://www.fon.hum.uva.nl/paul/praat.html

• Snack and WaveSurfer also contain a pitch extractor

Taking a step back... To get this working you MUST figure out a way to plot intermediate steps of this process. What you're trying to do is not particularly hard, but it is error prone and fiddly. Clipping, windowing, bad wiring, aliasing, DC offsets, reading the wrong channels, the weird FFT frequency axis, impedance mismatches, frame size errors... who knows. But if you can plot the raw data, and then plot the FFT, all will become clear.