AW: [sdiy] Filter Question

[Czech Martin]

Yes , it can be done if phase is observed.
For a one pole LP this works straightforward.
The interesting result is that you can build
a crossover with zero delta Phi, highpass and lowpass
share the same cap..., and frequency.


This is from my head , I forgot about the details
but I can look it up. 
Cascading such structures can yield steeper slopes.
Of course all real poles.

A related example is the old Formant 24dB filter.

For more interesting filters you have to equalize phase.
Verfy often this makes no sense, because it is easier
to develop a genuine highpass.

Well, in terms of noise or stability a lowpass substractor
could be deserireable, or at least I wouldn't exclude that.

Note that the resulting zero may be "off line",
i.e. DC leakage. 

m.c.
> -----Ursprüngliche Nachricht-----
> Von: Scott Gravenhorst [mailto:music.maker at gte.net]
> Gesendet: Mittwoch, 7. November 2001 16:44
> An: synth-diy at dropmix.xs4all.nl
> Betreff: [sdiy] Filter Question
> 
> 
> Can a lowpass filter be built by using a hipass filter
> output fed back to a summing amp that sums the original
> signal and the hipass output to cancel high frequencies?  
> My guess is "no" because of phase issues.  Lunatic minds
> want to know.
> 
> =========================================================  
> - Government: The other religion.
> - The media's credibility should always be questioned.
> - Lambs who lie down with lions are lunch.
> 
> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> -- Linux Rex         | RedWebMail by RedStarWare
> -- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html
> 
>