### FFT for Highpass, Bandpass, Bandstop filtering

Posted:

**Thu Mar 18, 2021 2:15 pm**I have been looking at your FFT Filter example program, trying to work out how I can use the FFT for other types of filters, namely: Highpass, Bandpass & Bandstop. But so far I have failed completely! This is probably due to my limited grasp of how FFT really works. I have tried reading all sorts of explanations but I just don't have the maths skills to understand any of it.

I had assumed that if setting the RealSpec & ImagSpec values above the cutoff gives you a Lowpass filter, setting the values below the cutoff should give you a HighPass filter but this does not work. I am hoping you give me some clues or simple examples of what I need to do to get these other types of filter to work.

You can download my modified FFTFilter code and app from this link if you want to see what I have been doing: https://we.tl/t-Zp5f5fetKm

Thanks in advance,

David.

I had assumed that if setting the RealSpec & ImagSpec values above the cutoff gives you a Lowpass filter, setting the values below the cutoff should give you a HighPass filter but this does not work. I am hoping you give me some clues or simple examples of what I need to do to get these other types of filter to work.

You can download my modified FFTFilter code and app from this link if you want to see what I have been doing: https://we.tl/t-Zp5f5fetKm

Thanks in advance,

David.