The Midnight Effect - Who-How?

@bbarten 

you asked: So, is this a consistent phenomenon?  Does it happen every time the circumstances are the same?

That’s a great question. Obviously it needs to be measurable and repeatable for it to be “real”. On the measurable side, it comes down to using and trusting one’s ability to discern differences in sound, much like reviewing a component or speaker positional change. I’ve no problem doing that, but I suspect that some other folks find it easier and some more difficult. So there’s no real standard for this type of measurement. As far as repeatability, yes it’s repeatable, but the degree of difference seems to be a variable and I haven’t been able to put my finger on why that is.

Verily, perchance an assay wherein copious amounts of potent spirits be administered at precise intervals might avail.

@whart 

PPS: I took a quick look at the PS Audio forum and there seems to be some suggestion that its regenerators are still susceptible to certain forms of noise. One user, John H, was a frequent contributor to those discussions.
 

I wasn’t aware of that line of discussion. So it would be interesting to find out exactly what that “noise” is, as it could be something that’s assumed to be fairly benign, whereas in practice it could be responsible for a very large affect on the reproduction of sound. I will try to find that forum discussion… thanks.

@tomic601 

You missed my comment about measuring you ambient noise floor at various times….. that’s ok….most audiophiles lack an SPL meter for level matching and other essential tasks…..

I caught your comment. It’s a valid enough point but I don’t think it’s responsible for the phenomenon that I’m talking about. I use REW for making room measurements and do notice changes in ambient noise levels at different times of day, but they’re very small changes. (Again, we’re in the boondocks and don’t have to deal with neighbors or road traffic noise). 
I can imagine some situations where it’s a significant factor in sound quality.

@knittersspouse okay that’s very interesting information. I hadn’t thought about electricity coming from different sources and each source carrying with it a certain type of “distortion”. That right there could be the answer I’m looking for. Skeptical me thinks that transformers and other components in the distribution network would remove these small line interferences but you seem to be saying not. Assuming you’re right, switches of this type should be noticeable and measurable using a ‘scope on the AC, right?

If you couple the psychological real effect in increasing sensitivity to sound at night with a more silent environment and generally no house heavy appliances working passed some late hours, less electrical disturbance in the neighborhood it does not need a Darpa research to feel a better acoustic experience in part resulting from decrease in the noise floor and more auditory sense relaxation ...😋

When i was doing my critical set of acoustics experiments for more than one year straight each day i waited in the evening late to verify the results and confirmed them or not,...Day listenings was not enough reliable...

By the way we do not remember sound details quality in a conscious way pass a very very short time. But my body remember it and remind it of some improvement or the opposite in the form of feelings when listenings...To experience this we must be totally relax with music we know completely well.. ..if it was not true i would have been unable to tune 100 resonators by ears mechanically . ( it was an acoustic puzzle because location matter)

By the way i never planned to do that, i make it one by one set of three without even knowing that it was a planned experiment at all i only go behind each small improvement and corrections ...More fun than buying  and we learn how to hear...

Then the improvement of acoustics parameters perception in the late evening is real ...