I’m working on new EQ project and I’m really interested in the differences between different equalizer types and does it really analog EQ can be better than digital one?
Imagine, you have to cut 2 frequencies from your track and you found 2 sweet spots for peaking cut filters.
What does your final frequency response should like? Most equalizers just sum your curves and you’ll have the result. Also don’t forget that for min-phase equalizers case the phase response of both curves also affects the result.
Green line is your final response. It is not what you’re expected! You spent a lot of time to find 2 sweet spots but as you can see that blue curve distorts red curve and vice versa and your sweet spots were shifted in frequency and in gain value. You should adjust red and blue curves again to return to your initial sweet spots, which is not good. This is how most min-phase equalizers work.
Now check the quote from this paper: [The Evolution of an EQ Design]
“(…) the only reason that I could see to use a topology using series connected EQ sections is to make their transfer functions additive. What does that mean? It means that if one were to make all the sections of an EQ design have the same frequency range, and then set each section to the same frequency and gain setting, they would add. If you boosted 1 KHz by 6 dB in each of 4 sections, the result would be 24 dB of gain boost at 1 KHz. (…)”
I suppose you’re familiar with such thing as “passive EQ”. Why they’re so great? I can suspect, because their transfer function is not additive. In passive EQ design our red and blue curves will lead to such final response:
It is very close to sweet spots we had, isn’t it?
Now check additive (red) and not-additive (blue) curves isolated:
And all curves together:
That’s why additive min-phase equalizers are very hard to tune right without proper frequency response graph, because each band affects each band. For non-additive equalizers it should be very simple to tune them by ear.
I can suggest that the right way to simplify the usage of additive equalizers is to calculate frequency and gain shift caused by band overlaps and to automatically compensate them.
This shift was caused by phase response overlaps but what do I think about linear phase equalizers then? Bob Katz in his mastering book wrote that linear phase equalizers have more analog sound. I think their predictable overlap of bands is one of the reasons of such statement. Unfortunately, they have great latency and due to that their usage is limited. I don’t choose linear phase for my EQ design. At least for now…