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?

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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

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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.