Super Best Audio Friends. I've been trying to find it myself. They ran pink or white noise through it and , while watching the waveform adjusted the dials. After the usual boost and cut, they started using the knobs against each other to make tighter, more pinpoint frequency selections. Its killing me I cannot find it.
EDIT: https://www.superbestaudiofriends.org/index.php?threads/schiit-loki-eq-measurements.5153/
As I said, all I'm looking for is a 2-3db cut at about 1500hz. Just a nudge for the dozen or so records that need it.