FFT on iPhone to ignore background noise and find lower pitches

Question

I have implemented Demetri\'s Pitch Detector project for the iPhone and hitting up against two problems. 1) any sort of background noise sends the frequency reading bananas

Answer 1

At the very least you need to apply a window function to your time domain data, prior to calculating the FFT. Without this step the power spectrum will contain artefacts (see: spectral leakage) which will interfere with your attempts at extracting pitch information.

A simple Hann (aka Hanning) window should suffice.