Dynamic Range: How Quiet is Quiet?

[OWC]

Although this is already a somewhat older post, I really would like to put a few things in perspective.
Actually this applies to a lot of conclusions being made on some articles on this forum (or maybe even in audio in general).

What I am really missing is some sense of context.
What I noticed is that most experiments (and conclusions) are done from a home/room type of environment.
There is nothing wrong with that on itself, but the story is sometimes totally different when using the same tools in a different environment.
One good example is a line-array system with something like 24 high-sensitive compression drivers with horns or waveguides.

In that case I can guarantee that everything worse than around 115dB SNR is just going to be very nasty.
Same goes for the other extreme, where the sensitivity of the drivers isn't an issue, but the fact that the environment is very quiet.

To put this in perspective, an average living room is actually a very easy environment.
So to answer the question; how quiet is quiet?
Well, that totally depends on the context and environment.

 

[MRC01]

I have a recording for testing dynamic range. It starts in a quiet park, the digital signal level is around -85 dB. This goes on for a while then a jet flies nearby and the signal smoothly goes to digital signal level 0 (just shy of digital clipping). When I play in my listening room, when the loudest part peaks at 106 dB SPL (measured at the listener position with an SPL meter, and it's broad spectrum so the meter is reasonably accurate), I can still hear the quiet part at -85 dB. Of course I can't measure the quiet part with my SPL meter because it's far too quiet. Assuming the system or speakers aren't compressing the signal, it should be 21 dB SPL. My room is in the basement and well insulated, so it's pretty quiet. But I don't think it can be THAT quiet. The sound should be below the noise floor of my room, but I can still hear it. On old RCA victor recordings from the 60s, one can discern low level musical detail in the tape hiss. Our ears/brains are pretty good at discerning correlated signals even when buried in noise.