BTW, an interesting thing about analog isolators as opposed to traditional analog EQs is that the former has the same (slightly degraded) sound quality regardless of the trim of that band… the group delay is always present and fixed. With normal EQs, at the 12 o’clock you should get no group delay phase alteration, since really the circuit should be doing nothing to the signal. On the X1800, the iso mode bypasses when all the knobs are centered… kind of a neat feature InMusic included, exploiting its digital nature to cheat it off. Unless an analog iso has a bypass button or switch, it’s always in the path. You can see its effects on a scope mutilating the test waveforms even with the knobs at their detents. A well-designed isolator, though, should be able to at least get the phasing right at the corner frequencies. Popular methods for isos and Xovers are Linkwitz Riley 4th-order and 2nd-order. In the latter method, you have to flip the phase of the alternating bands, but you get lower group delay than the former. Other filter methods (like Bessel) can produce even lower group delay phase distortion throughout, but then you end up with the bands not summing evenly at the corner frequencies… not an issue if you’re matching the filters to speaker response on a dedicated crossover (drivers vary in sensitivity and phase response anyway, so you can mix and match, attenuate, etc), but it’s an issue with an isolator that’s supposed to sum evenly… you know, at least be flat when all the knobs are centered.
And yeah, NY rotary DJs have historically liked big knobs and a lot of space in between them. For all the ham-handedness you’d assume about them with all that big chunky stuff to work, I’ve seen some of them show an amazing amount of finesse working touchy 45s.