When shooting IR's, the stimulus signal can be amplified through the cabinet with a neutral, reference style (no color/frequency deviation) amplifier, or with a guitar amp (via the "power section") - the latter potentially doing the job much differently. If using the "power section" of a guitar amp, the design of the particular model used can drastically change the coloring and frequency response of the original measurement stimulus material. This often results in a significant change in the frequency response due to the negative feedback controls (Presence / Depth) of the circuit, the tube type, among several other factors. Even having the Presence and Depth at zero, there are still usually a few tell-tale frequency deviations, one of the most noticeable being a scoop in the midrange.
Back in the early days of amp modeling, flat out - power amp simulation was just okay, to lackluster, to non-existent. At that time, it could be beneficial to have some of that coloring and frequency response alteration "baked in" to the IR, especially that mid scoop, and the boosts in the low and high resonance points of the spectrum. It didn't make the IR any better or worse or more fit for a particular purpose, it simply helped the amp modeling be more convincing in spite of its short comings, and served as an outsourced crutch to that symbiotic platform. This is of course in a generic way, as different amp designs result in varied frequency response deviations.
Since OwnHammer has been around since the beginning of when professional IR's were being offered commercially, the IR libraries often offered IR's shot both ways - with a reference amp, and with the "power section" of a guitar tube amp. As amp modeling became more competent and realistic, this turn key solution became less and less useful, and eventually was just bloat in the packages. At a certain point, OwnHammer only continued forward using reference amplifiers to drive the source. There were some who either stuck with those old platforms, or got used to dialing in their amps with that scooped sound baked into the IR that a guitar tube amp retains, so the OwnHammer PDF Manuals provided information about an "EQ Tip" that would help those still seeking that old sound of having IR's driven by the power section of a guitar amplifier. This tip has since been significantly misinterpretted and misused, and as it is no longer a relevant practice with the amp modeling world in its current, realistic state (for the majority of platforms), it has been removed.
- The EQ tip was to help old/bad modeling platforms, which had poor power amp modeling.
- The EQ tip is not a way for the IR's themselves to "sound more realistic" - in fact the opposite is true.
- The EQ tip is not relevant with newer, competent modeling platforms like Line 6 Helix, Fractal, Kemper, TH-U, etc.
- The EQ tip is now largely unnecessary and has been removed from the PDF Manual as today it does more harm than good among the newer user base that does not understand it (as many likely were not around for when it was relevant).