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I've been tasked with coming up with code to take a raw FTT (see example) and be able to apply a high/low-pass filter on it, and re-display the results. I know nothing about the math involved, or the input parameters, other than I assume the user of the app would select the cut-off (filter) threshold values...other than that I'm lost in the woods...

What I need is the most-basic algorithm for high and low pass filtering, based on the example below. If anyone has C# code to do it, that would be absolutely ideal.

Pre-filter FFT example: enter image description here

Thomas Ayoub
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Bazzy
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    Possible duplicate of [lowpass and high pass filter in C#](http://stackoverflow.com/questions/8079526/lowpass-and-high-pass-filter-in-c-sharp) – Cheesebaron Sep 08 '16 at 15:16
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    Please check this: http://dsp.stackexchange.com/questions/15902/low-pass-fir-filter – User1551892 Sep 08 '16 at 15:25
  • However, you have to do some maths to find out the normalized cutoff frequency and I hope you have access to some kind of c# math library where you could find convolution method – User1551892 Sep 08 '16 at 15:28
  • Learn the math and then write code... – Phil1970 Sep 08 '16 at 16:27
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    Phil - If I had time to commit to the "know nothing to know everything" for this task, I wouldn't be here. I have about a day. I'll check the examples quoted above...thanks. – Bazzy Sep 08 '16 at 17:24
  • A lowpass filter effectively zeros out the amplitude of the FFT samples (your image) above a cutoff (passes only low frequencies). A highpass filter zeros out the FFT samples *below* a cutoff, passing only high frequencies. A bandpass filter zeros frequencies below a lower cutoff and above an upper cutoff, passing only a small band. Since you’re given the FFT samples (which tell you the energy of the signal at each frequency), I’d think you can just zoom the x-axis to a min/max based on user input. – Ahmed Fasih Sep 08 '16 at 19:58

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