Unable to get correct frequency value on iphone

Question

I'm trying to analyze frequency detection algorithms on iOS platform. So I found several implementations using FFT and CoreAudio (example 1 and example 2). But in both cases there is some imprecision in frequency exists:

• (1) For A4 (440Hz) shows 441.430664 Hz.
• (1) For C6 (1046.5 Hz) shows 1518.09082 Hz.
• (2) For A4 (440Hz) shows 440.72 Hz.
• (2) For C6 (1046.5 Hz) shows 1042.396606 Hz.

Why this happens and how to avoid this problem and detect frequency in more accurate way?

Answer 1

Resolution in the frequency domain is inversely related to number of FFT bins. You need to either:

• increase the size of your FFT to get finer resolution
• use magnitude of adjacent bins to tweak the frequency estimate
• use an alternative method for frequency estimation rather than FFT e.g. parametric model