| It's your own fault that they all sound the same.
One reason most (non-linear phase) digital EQ's sound similar is that audio engineers expect the user interface to have the same cannonical controls: Gain, Freq, and Q. This leads designers down the path of bi-quadratic filters, which drastically reduces design freedom.
Having decided on cascaded bi-quads, the majority of programmers will pull down the same DSP cookbooks: Zölzer, Bristow-Johnson, and (if they want to do "decramping") Orfanidis.
Now back when everyone coded in fixed-point, there was still room for variation due to internal architecture. Different signal flow graphs produce different internal roundoff errors with these various errors being "noise-shaped" in different ways. But in practice, the optimal state space forms were seldom used, because they were less efficient than the standard formulations.
Now that many plug ins are being coded in floating point, internal architecture doesn't matter quite as much. But of course the programmer can intentionally put saturation features at certain internal nodes. The result will depend on the topology, but since these topologies may have little to do with analog topologies, it's not clear how this will satisfy the expectations of a typical user.
Digital EQ's don't have to have either minimum phase or linear phase -- other choices are possible. The question is whether these other choices are "musically useful." The truth is, our music has been shaped by minimum phase EQ's for so long that we might not even want something else.
If we restrict ourselves to minimum phase, interesting things are still possible. But to get them, we have to break free of the "tyranny of the bell curve". Think of how a graphic equalizer curve looks if you just push up one fader. Now imagine that curve having a different shape: it might have steeper sides, a broader top -- it might even be asymmetrical. There could be a knob for the plateau width, several choices for the skirt slope, and a knob to control the skew. It's really no problem to build such things in DSP, but the question is: would you use them?
Would you be willing to learn that part of your craft all over again? Or do like the fact that you already know how to use an EQ?
David L. Rick
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