How to make a RTA analyser in Iphone

Question

Hi Guys

I want to make a RTA for audio. I will try it by the aurioTouch sample code but i did not able to make that actual RTA, I want to make RTA on the basis of octave and 1/3 Octave.

Please suggest me the right way.

Thanks, KD

Answer 1

What you might want to try is an array of bandpass filters with your desired frequency response (octave or 3rd octave bandwidth, transition width, stopband attenuation, etc.), which you can implement using standard DSP IIR (or perhaps FFT overlap-add/save) filtering algorithms and techniques. The aurioTouch example already shows you how to get the audio samples to feed your chosen filtering process. Then plot the calculated magnitude response out of each filter (for example: from an envelope follower) at your desired time step.

There are plenty of Digital Signal Processing tutorials and resources on-line: Bores, Wikibooks, DSPGuru, DSPGuide, etc.