Hi Tim, Hi everybody,

I want to apologize for continuing this thread. I don't want to do any math here. I hope I can clarify this interesting theoretical discussion, where I have learned a lot and I hope some others as well.

> tan^-1(-5*w + 3*k*w - 5*w^3 - k*w^3 + 14*w^5 + 22*w^7 + 7*w^9 - w^11)/
> (1 + k - 7*w^2 - 3*k*w^2 - 22*w^4 - 14*w^6 + 5*w^8 + 5*w^10)

This is not the the function which tells you how the phase changes, when you changes the filter!
The transfer function and the phase function above describes how the filter affects the input signal in a _steady state_.

I think you mean the phase delay, which is:
http://homepages.physik.uni-muenchen.de/~oliver.gretz/a-100/phase.pdf
(taken from "Analog Filters Using MATLAB" from Wanhammer)

Cheers,
Ollie