It can start right at the source point itself. Issues in microphone power supplies, bad microphone circuitry, bad microphone choices, bad microphone preamps, bad mixing board wiring, bad mixing board power supplies, bad mixing board circuitry, and so on, down the line. It’s a very involved set of subjects.
Certain aspects of the human voice can emphasis this and if the recording engineers are not cognizant of this issue being possible in each stage as mentioned.... then each part of this chain can be bad, and then it all adds up... and we get "screech-mud" for a a sonic result.
How much music have you heard that sounds like ’screech-thump, screech-thump’, on and on and on?
Sometimes good recordings are an accident, sometimes it’s intentional.
It’s a crap shoot, as they say. Bad? Bad we can find anywhere.
Bad is so easy to find that people have come to think that gear and recordings all sound that way. That the distortions are inherent to the situation and they don’t actually listen, they project what they know into it. (the human body is wired for this automaton behaviour)
Teaching people otherwise is a monumental task.
It’s the very heart of the audiophile conundrum. Some get it, some don’t. It’s why we have such threads as cable debates. Some people live with an outward projection only, and some have a two way path of awareness, which is what is required to build a self beyond the basics.
Life is too short and we are only marginally learning and cognition machines...... we are principally unconscious mimic, copy, and mirror -- absorption machines.
If you watch yourself carefully you can see it in action.
Thus:"Give me the child for the first seven years and I will give you the man."
(Voltaire falsely attributed it to Ignatius of Loyola, as a barb at him - Voltaire was not fond of such, the correct origin is Aristotle)
Intelligence is a long slow walk back through the cluttered forest you came from.