How to find the fundamental frequency of a guitar string sound?

Question

I want to build a guitar tuner app for Iphone. My goal is to find the fundamental frequency of sound generated by a guitar string. I have used bits of code from aurioTouch s

Answer 1

Finding the musical pitches in a chord is far more difficult than estimating the pitch of one single string or note played at a time. The overtones for the multiple notes in a chord might all be overlapping and interleaving. And all the notes in common chords may themselves be at overtone frequencies for one or more non-existent lower pitched notes.

For single notes, autocorrelation is a common technique used by some guitar tuners. But with autocorrelation, you have to be aware of some potential octave uncertainty, as guitars may produce inharmonic and decaying overtones which thus don't exactly match from pitch period to pitch period. Cepstrum and Harmonic Product Spectrum are two other pitch estimation methods which may or may not have different problems, depending on the guitar and the note.

RAPT appears to be one published algorithm for more robust pitch estimation. YIN is another.

Also Objective C is a superset of ANSI C. So you can use any C DSP routines you find for pitch estimation within an Objective C app.