Manipulating with frequencies through fftw I'm using portaudio for I/O audio streaming, and I wanted to apply some equalization on audio input from microphone. I found that most people refer to fft for task like that, so I use FFTW library in my project. My first idea was to select frequency bins in some range, from fft resulting complex array, and  increase their amplitudes by scaling them with some factors. But this resulting only in noise,  there is no sign of any equalization. So my question is, is it possible to increase volume at specified frequencies, through fft, and if so, how to do that. My experience so far makes me think that any change of those values in fft complex array just destroys the sound. Is there a proper way to manipulate with that complex data from fft resulting array?
Any tips for equalization other than fft are also welcome.
You applied the FFT to the full signal? Then modification of the amplitudes will likely destroy any time locality.

Use the so-called STFT, short term Fourier transform, or overlap-add method to get a time-localized frequency analysis.