How can we amplify sound with specific frequency in iPhone?

Can s开发者_运维问答omeone tell me how we can amplify the sound of specific frequency alone?

Actually, you don't need to use FFTs for this -- digital filters are very computationally efficient, needing just a few multiplies and adds per sample being processed.

A good resource for the implementation of this is Robert Bristow-Johnson's Filter Cookbook. There are also good digital signal processing tutorials at Stehpan Bernsee's DSP Dimension

You can use any one of many DSP (digital signal processing) techniques or filters, including IIR biquads (commonly used in audio equalizers with minimal CPU/DSP performance capability), FIR filtering by direct convolution, FFT overlap-add/save convolution, etc.