Parametric EQ Schem

[Martin Czech]

> I don't have it but there was one for the Elektor Formant. It isn't in 
> the books though, do any of the Formant nutters know where to find it?

Right : In the Formant Part 2 (Blue Book), they called it Resonance Filter,
there were three state variable bandpass summed together, so one gets 
three variable 2-pole "peaks" in frequency domain. 

"http://www.tellus.vallentuna.se/gymninfo/personal/anders/andersus.html"

(Not functional at the moment, don't know what happened to the page).

If one substracts the filter outputs
from the input instead of adding, one can also get "notches", both
options can be combined by an add/substract circuit, so that one can
get notches and peaks as desired.
If one uses a simple sweepable 6dB lowpass instead of bandpass, one can also 
add a shelving characteristic, which gives greater bandwith, if you like.


m.c.