[sdiy] DC 'bounce' in second order filters

[Magnus Danielson]

On 11/23/2011 03:06 PM, Harry Bissell wrote:
> OK let's try this
>
> I have a second order VCF  When I first apply a signal to it (starting from a zero condition) the filter
> have a DC bounce (of one polarity or another) which prevents the signal output from crossing zero for a couple of cycles.
>
> The overall shape of the bounce looks critically damped, it overshoots in one polarity then recovers in the other polarity before becoming
> DC stable. The filter is not resonant (Q=.707 or so I believe)
>
> Is the bounce an unavoidable artifact of a second (or higher) order filter, or can I do anything to reduce it. In my application missing a zero
> cross is an error condition I'd like to avoid
>
> your thoughts ???

You see the step response of the filter. It's the natural consequence of 
a second order filter. Get used to it and live with it.

You can always tweak the resonance and see the how the oscillations 
changes. :)

So, it is unavoidable.

Cheers,
Magnus