[sdiy] Making a HPF using a LPF...??

[Scott Nordlund]

> > Actually, this sort of filter-stage summing is done all the time, and it works quite well.  This is, after all, how the highpass response is derived in a state variable filter.
> 
> I'm not sure I would describe it exactly like that, since it's part of the entire feedback loop that makes the SVF tick... not that I'm sure how I would describe it. ;)
> 
> - Aaron
If you relate it to control theory you can call it an error signal.