Allpass filter with 180 degree phase shift instead of 360 degree
I want to build an allpass filter but i have not found out how to adjust the phaseshift of it. There is only the option to adjust frequency and Q factor as far as i know. Or is there a better way to implement this?
In the picture below i illustrade it: The orange line ist the actual phaseshift and the blue line is the phaseshift i want to achieve.
Hello,
Try the First-Order Allpass Filter. It has just one pole-zero pair instead of two, thus provides half the phase shift (red trace):
Best regards,
Bob
Hey, thank you! I just read that first order filters have no Q factor. How would you manipulte the steepness of the curve? Is there a way to have streep curve but only 180° shift?
Sorry, I don't know how to make these two requirements compatible. To my limited understanding, steep slopes need more poles and zeros in their transfer function (thus, a higher order filter). That's why first-order filters have no Q adjustment -- their Q is stuck at a very low value. But those poles and zeros mathematically produce more phase shift, making the filter shift more than 180 degrees. Perhaps another member knows a better way to suit your application.
Best regards,
Bob
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