ok I have a working FFT I have test that... I just make a IFFT... and I added a FIR filter. so i am testing it and I send a sin wave in to the FFT and then to the Filter and then to the IFFT. after the FIlter every things looks good. but after the IFFT it does not. 1) the points are way too high 2) there should only be one Frequency but there are not you can download the code here: https://onedrive.live.com/redir?resid=CC8AF223519E2440!117&authkey=!AFIp89IzzQnSNgg&ithint=file,.zip any help would be great.