This is a broad sweep at the issue, some guesswork & experimentation required.
First of all, if you have an alternative DAC try it, no matter how basic, just to eliminate the simplest explanation.
Secondly - if anything has batteries, replace them.
Up at 5k, it's unlikely to be directly related to 'mains hum' itself, grounding issue etc.
A very simple ...
Not really worth discussing the positioning of the mics other than to say they are just dumped in the middle of the stage with no real consideration for the soloist or the recorded sound.
The mics are schoeps colette series. It's not possible to tell what capsule is being used. Probably MK2s or MK21. They are used with active extension tube.
Thanks for all the informative explanations and helpful metaphors AzulShiva.
I have a different low frequency problem. I think it's related to this question but please correct me if I'm meant to make a new post.
I'm subjected to a technical problem in the floors of a 4 story building. Basically everyday walking becomes amplified through the floor into the ...