Using Apple's Accelerate framework, FFT, Hann windowing and Overlapping

Question

I\'m trying to setup FFT for a project and really didn\'t get a clear picture on things... Basically, I am using Audio Units to get the data from t

Answer 1

You don't actually need to overlap - typically frames are overlapped to give higher resolution in the time axis, e.g. for plotting spectrograms or for estimating note onset times. You could just get your code working without overlapping for now, as it's less complicated, and then decide whether you need higher resolution on the time axis later.

If you decide you do want to add overlapping then you will need to save a chunk of the previous buffer (e.g. 50%) and then for each new buffer you will process two complete buffers as follows:

• process last 50% of old buffer + first 50% of new buffer
• process 100% of new buffer
• save last 50% of new buffer for next iteration

For different overlap percentages a similar logic applies.

Note that increasing overlap beyond a certain point can become counterproductive as the required processing bandwidth increases greatly with little gain in resolution.