It's called Zynaptiq Unfilter Real-time Tonal Linearization Plug-in. The Sweetwater website does a lot better job than I could to explain what it does and how it works.
https://www.sweetwater.com/store/detail/Unfilter--zynaptiq-unfilter-real-time-tonal-linearization-plug-inIt was recommended to me by a Grammy-winning mastering engineer who does a lot of restoration work on vintage recordings. When he learned I was working almost exclusively with audience recordings, he strongly suggested I check it out.
I've always been skeptical of black box or one button solutions, but this seems to be another in the emerging line of machine-learning based plug ins that do what we never thought possible. The first bullet on Sweetwater sort of sums it up:
"A mind-blowing audio restoration plug-in that automatically detects and remove resonances, equalization, roll-offs and the effects of comb filtering"
I have found it incredibly useful on shows recorded with low-end gear, often restoring a musical fidelity of highs and lows that was nothing but a boxy, muddled mess otherwise. Some recordings don't take to it at all. Others it is like magic, shifting a recording from unlistenable to listenable or good to very good.
It seems to compensate for resonances that can mask what's actually on the tape, like moving a pillow that was blocking the speaker.
I don't use it on everything and there are times when it can seem to take away "forwardness," for lack of a better word, in vocals. But it often makes low-end and mid-range tapes sound so much more musical and natural, which says a lot about a processor.
Again, I would only recommend it to those dealing in vintage, mid-grade audience recordings as that's where it will serve you best.
Would love to hear if others have used and what you make of it. I believe there is a free demo. I have nothing whatsoever to do with the company, which I think is based in Germany, but it has become a very powerful restoration tool for me.