[LAD] Help with frequency domain filtering basics

Hi, I'm trying to do a simple effect in the frequency domain, nothing extraordinary. I need to apply various gains to specific frequencies. For this purpose, I want to process a 16bit audio input stream, block by block, apply a hanning window, do a fft, now apply my effect, and then an inverse fft, followed by overlap and add buffering. For now, I'm simply trying to do all of this without applying any effect, just to see if my time to frequency and back conversion is correct. I managed to do this in Octave. Now, I'm trying to do it in C with fftw and the sound I obtain is like "shivering". It's recognizable but severely altered. I've spent hours on this, it just won't work. Attached : - freqfilter.m: my working octave version - transform.h and transform.c: time -> frequency -> time routines - transformtest.c: test program Could anyone tell me what's wrong with this C code? Thanks in advance -- Olivier