Drum EQ is a static/dynamic EQ who's frequency centers are set to octave multiples of the resonant frequency of the drum. A secondary, "Alternate Resonance" can also be added to subtly or drastically change the character of the drum as well.
How often when looking at old mixes, do you find that the cuts and boosts on your drum eq's are centered around multiples of the drum's resonant frequency? Perhaps this realization has led to you always keeping a calculator app open?
At AIXDSP, we don't just want to get rid of unnecessary mouse-clicks, but unnecessary calculators as well!
Loop a section of the drum in question and turn the "Tune Frequency" knob until the blue vertical line on the spectrum window lines up with the fundamental resonant frequency of the drum. You will see that all of the EQ frequency centers have now changed to octaves of that new "Tune Frequency". In many if not most cases, you will also see that the drum itself has some strong peaks or dips that those frequencies.
Try cutting and boosting at these different octaves and rejoice in not having to fiddle around with calculators, fine tuning and direct entries just to get the frequencies right. Got it wrong? No problem, turning the "Tune Frequency" knob automatically adjusts all bands across all octaves!
Set the "Alternate Resonance" knob above or below the fundamental frequency of the drum (think of this very much in terms of how you tune your tom's bottom head compared to the top head). Turning up or down these band gains can have a very strong impact on the "harshness" or "smoothness" of the drum sound in total.
You may have long ago noticed a phenomenon whereby turning up the gain on octaves above the fundamental often sounds extremely similar to turning up the fundamental itself.
This has enormous uses:
You can definitely trick the ear into thinking that small speakers are putting out a LOT more lows because of this trick. Experiment with this sort of thing if you haven't before. Its amazing just how much low bass it feels like the sound has even through an iPhone speaker\
Because of the property above, you can carve out space in a mix by moving what seems to be the resonant octave up an octave or so, the classic case of making room for the bass guitar by moving the kick up.
And all this is before we get into the compressor/expander on every band, including a hold control!