iOS: Record audio below some certain frequency

Question

I am working on an app in which I have to perform recording from iPhone's microphone, but my requirement is to record only voice below some certain frequency. All other voice more than this frequency should not be record.

I know SO already has many post on this, but I couldn't find any helpful.

I find the frequency by using this code:- http://www.ehow.com/how_12224909_detect-blow-mic-xcode.html

But I am getting trouble to avoid this frequency being recorded.

Can anyone suggest me how to do this or If any lib/open source is available. Any help on this will be appreciated.

Thanks in advance.

Answer 1

First I would check if the microphone of the device can detect frequencies in your Band Width.
Second iOS comes with an amazing framework called accelerate here you can find vDSP library (digital signal processing) with those functionalities:

• Vector and matrix arithmetic
• Fourier transforms
• Convolution, correlation, and window generation
  

Accelerate is very efficient set of functionalities, powerful and performant.
Your problem seems to be a matter of filtering (mostly).
Here a sample from Apple, Using Fourier transform.