[sdiy] Q?

[Czech Martin]

>There are definitions in the time domain, based on decay of the ringing of the
>filter when excited with a pulse or step.
>
>I think for 2pole BPFs the two definitions mean the same thing.
>
>For higher order filters, you have individual Q's for the individual
>pole pairs. (I don't know if there is a definition of Q for the overall response
>of a higher order filter. If there's something like that, I never use it.)

For a bandpass one could define a similar frequency domain bandwidth/frequency
ratio.

You are rigth, usually the individual 2nd order Qs are given/defined.

The interesting thing is, that the lowpass Q in this sense makes no sense
when the Q is below 2 or so, because not peak is visible.
Same for highpass. And for the noth you usually have not 0 gain
for the resonance, but a little speak through, this will add at least
a zero, and then the formulas are not that nice any more
(the half power thing comes really handy for the ideal bandpass, so
that after a while nice short expressions come out of it).

In some book I reqad about the ratio of real power vesus reactive power
inb LCR circuits, this can also be a definition of Q.
But I can not find this any more.

m.c.