High pass

Hello,

An FIR filter with a symmetrical coefficient list ("kernel") delays its input by half its length. Thus, your 175 tap filter has a delay of 87 samples. This delay produces a constantly increasing phase lag with frequency. As your input frequency increases from zero (DC), the phase lag runs through many whole cycles of phase shift, causing the LP filter's output to subtract at some frequencies and add at others. Thus your response is not as expected.

To fix this, add a compensating 87 - sample delay to the unfiltered signal before the subtract. Please download the file below and look at it in SigmaStudio -- for some reason inserting pictures is not working for me today.

Best regards,

Bob

High-pass.zip

Effectively, I had forgotten this factor...Thank you Bob.

Just a minor nitpick, it's not half of its length but half of length-1. 87 being (175-1)/2, not 175/2.