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58 | FOCUSING EQUALIZER
capture the entire behavior of a unit in one big
sweep. The disadvantage is that the math can get
very complicated, even for circuits that doesn’t look
complicated at all. Even a simple thing like a bypass
(such as in the Filtek) is complicated and causes
problems when modeled, and it would be easy for us
to take a short cut and mimic stuff when the mod-
eling gets tough. But we don’t do that at Softube,
because we believe that you can hear the difference.
So we do real modeling, for good and for worse.
Credits
Niklas Odelholm – modeling and graphics design.
Torsten Gatu – concept. Oscar Öberg – frame-
work programming. Arvid Rosén – framework
programming. Ulf Ekelöf – graphics rendering.
Thanks to Stefan Fandén and the crew at Deluxe
Music for letting us borrow the gear!
Differences Between Passive
and Active
This table highlights some of the differences be-
tween the three equalizers. Please note that there
are a lot of other differences that make up for the
characteristic sounds, and not many of these are
easy to put in a table like this.
1) The Passive EQ doesn’t have any cutting bell
filters.
2) “Constant Q” wasn’t defined at the time that the
Filtek was built, but it shows many properties of a
“Constant Q” equalizer.
3) The cut filters are shelving in the Passive Equal-
izer (due to parasitic resistance in the inductor)
while this (unwanted?) property have been removed
in the Focusing Equalizer.
Finally, a Note on Modeling
There are lots of buzzwords when it comes to recre-
ating old gear in the digital domain. Many are those
who claim they “model” stuff, few are those who
actually do it. The advantage of real, component-
based, physical/mathematical modeling is that you
Active Equalizer Passive Equalizer Focusing Equalizer
Symmetrical Bell
Shapes
Yes N/A (1) Symmetrical (Active),
Non-symmetrical (Pas-
sive)
Constant Q
Yes, sort of (2) No
High/Low Cut 18 dB/oct. Shelving, 6 dB/oct. (3) 6 dB (Passive), 18 dB
(Active)
Filter Types Bell 3-pole filters Shelving 6 dB/oct. (High/Low)
Bell 1-pole filter (Presence)
Isolated Bands Yes No