If you're new to Magic Lantern and need a getting started guide, here is an in depth tutorial I created :)
With a sample editor that can use VST/AU effects, and the free version of this, or something that has the same functionality: https://www.tokyodawn.net/tdr-nova/
1. take a frequency band, put the Q for it to max or near max, and gain to max.
2. sweep the frequency until you find the one that makes it sound extremely boxy (it's probably below 1k but don't take my word for it, you will hear it when you found it however)
3. now set gain to zero, activate the threshold button, and dial the threshold to a value that just makes the boxyness disappear without making it sound too thin
4. repeat with more frequencies as needed/wanted
5. compress or normalize
> resonances of your room/speakers/headphones
Yet the frequencies that stand out depend so much on the input material, and arent't the same between recordings in different rooms or with different mics, even with the same playback setup. Weird.
As the manual of that VST so terribly states
> This is an excellent tool to correct a boxy low-endsound, even out resonances in a recording or reduce excessive sibilance in a vocal part.
Sure, they don't outline this specific approach, but others do, sadly:
https://www.soundonsound.com/sound-advice/q-how-do-pinpoint-...
> In my experience visual analysis won’t usually help a great deal here, and you have to adopt more of a ‘hunt and peck’ approach, sweeping a narrow EQ boost around the spectrum and then placing an EQ cut wherever the boost sounds most unappealing
And it just goes on and on :(
http://indierecordingdepot.com/t/how-do-i-find-resonant-freq...
Of course, since you said it's such terrible advice, my ears noticing the results are probably lying to me, and I can hardly wait to find out how to do it correctly at last.
Just because something is repeated a lot doesn't automatically make it a great idea: see "Brexit means Brexit" or "Build The Wall" for examples.