19 Nov
2017
19 Nov
'17
12:21 p.m.
On Sun, Nov 19, 2017 at 01:23:44AM +0100, David Kastrup wrote:
Now the EQ section of the Onyx mixers has been
designed by Carl Perkins
and is liked by a few people. Since it has to get along with not too
many elements and uses opamps, the actual equations for the various
sections (shelved low-pass, parametric mid pass(es), shelved high-pass)
are comparatively simple and basically amount to comparatively simple
transfer functions yielding themselves reasonably well to bilinear
transforms and consequently low-order IIR filters.
Indeed, and that basically means there is no point in 'emulating' those
filters.
Take a for example a second order parametric section. If it has controls
for center frequency, bandwidth and gain then it can generate *all*
frequency responses of that type (within the range of its controls).
There or no more free parameters given the order and the general shape
of the frequency response.
In other words, any such filter can do whatever any other can.
What makes EQ sections of the same type different is how control settings
map to actual parameter values or how they interact, for example how the
effective bandwidth changes as a function of gain. This will give then a
certain 'feel'. But it doesn't make the actual EQ different.
Ciao,
--
FA
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