FFT problem

[anyang]

Hello,

      I'm a new to Labwindows/CVI and FFT. Now, I get 512 datas with 2 second. I want to get rid off the influence of low frequency.  First I compute the Fast Fourier and Transform by FFT, and filter the signal using a Butterworth lowpass digital filter. Then caculate the inverse Fast Fourier Transform of this data. But I can't get the right number.

     I'll upload the project, and hope you can help me get through it.

     Thank you for your help in advance.

[Wolfgang]

Did you have a look at the sample analysis\narrowbandfilter.cws? This example provides four filter types (low pass, high pass, band pass, band stop) and might be helpful in your case.

[dcl9000]

anyang,

I looked at your code.  Bw_LPF(...) is not that complicated. 

If you just want to filter out high frequency noise from the original signal, simply use Bw_LPF(....) on the original time-domain data.  You don't need to use FFT to change the data into frequency domain and then apply the Bw_LPF(...) function to the data in frequency domain.