[sdiy] Multimode pole-mixing - building notch responses

Richie Burnett rburnett at richieburnett.co.uk
Sun Sep 16 18:15:52 CEST 2018

> If you have a Macintosh, there's a very nice math utility built in called 
> Grapher...
> And fill in your transfer function within that:
> y = abs((s^2 + 1) / (s^2 + s + 1))

If you graph this Tom, try varying the coefficient of s in the denominator 
polynomial within the range 0 to 2.  This is what determines the Q factor of 
the complex poles, and moves them closer or further away from the complex 
zeros on the jw axis.  And it is this coefficient that ultimately makes the 
notch narrower (with values close to zero) or wider (with values close to 


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