Is there any chance the microphone was in a slightly different location or an adjacent piece of furniture was moved between measurements?
I can see no reason why differences between the various digital connections would cause what you are showing, but moving the measuring microphone, or a reflecting surface near it, a few cm would do exactly what your measurements show (except the optical result ???).
All your plots look like the errors are down to room reflections, as if the room is a very sparsely furnished modern style room (which are hopeless for good sound quality, unfortunately) or reflections from a hard surface near the measuring microphone.
I can see no reason why differences between the various digital connections would cause what you are showing, but moving the measuring microphone, or a reflecting surface near it, a few cm would do exactly what your measurements show (except the optical result ???).
All your plots look like the errors are down to room reflections, as if the room is a very sparsely furnished modern style room (which are hopeless for good sound quality, unfortunately) or reflections from a hard surface near the measuring microphone.
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