Man. At its best, it's a small sliver of inaudible frequencies at inaudible volume levels. At its worst, it's a whole mess of noise and distortion. I'm beginning to think that the guy who downsamples all of his HD tracks to 16/44.1 is on the right track.
I've been saying that for years, well over a decade. Consumer distribution has moved on to higher and higher sample rates, marketing it as more accurate and/or as capturing more of the "real" sound but that's all it is, marketing! Absolutely ALL eventualities, including ANYTHING that may happen downstream, is MORE THAN covered by 24/48 and that's not just for music but for all audio. Beyond that point it's all downhill, not uphill as suggested by marketing.
[1] So, above 20 kHz spikes and other noise not related to music itself most likely it is not intentional, but probably next to unavoidable in real world situations. [1a] And is something to be added to the "watch for and avoid" list for the future recordings.
[2] Now, imagine a multichannel multimiked recording ... using say at least three mic preamps from at least two manufacturers.
[3] Unless the equipment is not strictly vintage ( with decent and solid linear power vsupplies ), all those switching power supply frequencies are bound to find their way trough all the cabling, one way or another.
[4] Even in balanced XLR connection, there is something called common mode rejection ratio - CMMR - and it definitely is NOT infinite; some of the noise ( including > 20 kHz ) WILL come trough .
1. Of course "above 20kHz spikes and other noise" is avoidable in real world situations, what a ridiculous thing to state. Simply choose a 44.1kHz PCM sampling rate and everything above 20-22kHz is COMPLETELY avoided!
1a. How do you propose to "watch for and avoid" it? Your solution makes no sense, record everything up to about 1.4Mhz and then what, how can you "watch for" anything above 96kHz? And, between 20kHz - 96kHz how does "watching" help, how can you tell from "watching" what is noise and what *might* be musical material? And, even if you do spot some obvious interference or noise, how do you propose to remove it, aren't you going to filter it out? Why don't you apply a bit of logic and filter it out to start with?
2. Why imagine that, why would one use different mic pre-amps from at least two manufacturers?
3. Why makes you think 20/30 years and older equipment had better power handling than today's pro equipment? Maybe if you compare top of the line vintage gear with today's cheap amateur/pro-sumer gear then in *some* cases the vintage gear might have the edge. Of course that's a nonsense comparison though, by definition commercial/professional recording studios are not based on cheap amateur gear!
4. What do you mean "some of the noise will come through"? Absolutely ALL of the noise will come through! You don't seem to understand what CMR is or what it does. CMR does NOT reduce/reject noise, it only rejects Common Mode noise, IE. Noise/interference introduced to the XLR connectors (and the cable between them) that is common to the hot and cold connections. Any noise before or after, such as recording venue noise/interference and mic and mic pre-amp self noise, is completely unaffected!
G