Back in 1996, it was possible to find digital EQs with true precision problems (limit-cycles). But nowadays with cheap 64bit processing available, it is trivial to push precision problems into -180dB nirvana.
As you can read in the EQ thread, I suspect that the fact that we're comparing apples and bananas. An analogue EQ signal path almost always looks like this (remember, context is mastering):
[DA] -> [EQ] -> [AD]
(where the EQ block itself consists of several non-linear elements such as in/out transformers and a fancy amp)
A digital signal path looks like this:
[EQ]
(without any non-linearity)
It's really difficult to compare and value both.
I suspect that the relatively high distortion transformers produce at low frequencies has a positive effect on the otherwise quite "destructive" nature of a pure EQ. When it comes to music, a pure high pass filter can be something really aggressive and "brutish". It changes the harmonic ratio where it "hurts" the most: The fundamental. It is well known that brain can "re-construct" a missing fundamental given a proper harmonic structure.
To address your question, SlickEQ uses no "tricks" except a good filter structure and high precision. The point is, most half-way ok recordings already contain such harmonics, trying to add more doesn't really improve the situation in the general case. And I suspect this is the reason why even mastering engineers with fancy gear sometimes opt for the clean digital EQ sound they don't find anywhere else.
But it sounds like an interesting option for the Gentleman's Edition.
).
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