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-   -   Audibility of noise (http://www.diyaudio.com/forums/everything-else/223716-audibility-noise.html)

mr_push_pull 16th November 2012 10:12 PM

Audibility of noise
 
this has been one of the most intriguing issues in audio, for me.

I did some experiments involving the lowest audible signal.
I determined that with close to ideal conditions (all doors closed, moment of day when extraneous noise is minimal, no computer or AC turned on etc) in my listening room the lowest audible signal (at 4kHz where the ear is most sensitive as per Fletcher-Munson) at the input of my speakers is ~0.2-0.3 mV RMS. I listen ~2 meters away from the speakers. as a sanity check, taking the absolute hearing threshold into consideration, I converted that back to 1m 1W/1m sensitivity and the error was minimal compared to manufacturer's spec.

with my DAC turned on and amp volume set to max I can barely hear any noise with ear next to tweeter. obviously, there are many systems with much lower noise floors (absolutely inaudible).

now, this made me wonder... many seem to be preoccupied with reduction of noise to unbelievably low levels. is there any reason to think such noise is detrimental to sound quality? if so, what is the mechanism of audibility?

how can noise that is absolutely inaudible when isolated affect the listening experience when one listens to music?

Enzo 16th November 2012 11:57 PM

One way might be that the noise signal might interact with the intrended signal, causing some artifacts.

Then of course there is marketability. Even if your noise floor is 100db down, and so inaudible, if someone can claim their system has a noise floor 110db down, then a lot of people will think "gee, that must be better." And then 120db down, and so on until you get to levels that the laws of physics won;t even allow.

Even if you are building it on your own, and not marketing anything, some people enjoy the challenge of seeing how far they can push some specification. At the far end of the scale are the competitive car audio competitions, where they go for the loudest possible sound they can cause to come from a speaker in an automobile. An utterly useless and pointless exercise from the point of listening to anything, but they get off on simply making a louder sound than the next guy. Bragging rights.

dewardh 17th November 2012 12:44 AM

Quote:

Originally Posted by mr_push_pull (Post 3244422)
is there any reason to think such noise is detrimental to sound quality?
. . .
how can noise that is absolutely inaudible when isolated affect the listening experience when one listens to music?

No.
. . .
It doesn't.

It's like the noise the tiger makes as it leaps from the tree onto your back. If you don't hear it . . . it doesn't matter.

mr_push_pull 17th November 2012 12:58 AM

Quote:

Originally Posted by dewardh (Post 3244557)
No.
It's like the noise the tiger makes as it leaps from the tree onto your back. If you don't hear it . . . it doesn't matter.

nice hyperbole but that's not what I asked.


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