>> For me, noise masking is an academic dead end. I understand, from the pr=
inciples of 'data reduced' audio storage formats, that there are psychoacus=
tic factors that can be bundled up into theoretical sumations of reproducti=
on perception.=A0 I get the idea that we can be fooled.
>>
>> I also get the idea that I'm sick and fed up of being fooled, too.
>
> You are not being "fooled" unless you think your ears are fooling you.
>
>> If you can hear it, it noise.
>
> If you can hear it, it's sound. If you don't want to hear it, it's noise.=
>
>> The fact that there are other noises in the spectrum, doesn't mask anyth=
ing. It's additive. If an orchestra of "noises" played together, would you =
ignore all but the loudest=A0 component ?
>>
>> I don't think so.
>
> But your ear-brain axis does "think" so. Masking exists as an empirical f=
act. In this case your intuition is wrong.
Robin,
Please may I add to your excellent reply? Noise is just part of hearing
sounds. Listen out in a quiet place and what can you hear? Your own
breathing for a start. That's part of your "self noise".
"Self noise" sounds nice and technical but it is only noise from one part o=
f
the recording chain.
Any noise rating requires a defined threshold level in comparison.
The fundamental acoustic noise threshhold level is the noise produced by th=
e
vibration of air molecules. "Excess noise" is the level of the apparent
noise above thermal noise. Now comes the snag - thermal noise rises with
frequency at 3dB per octave, and our ears hear low level noise approximatel=
y
according to the A-weighting or IT-U 468 curves. The best field mics can do=
is 10dB to 13dB weighted excess noise above thermal noise.
Unless properly defined, this is not related to "self noise".
On a "perfect" mic, the excess noise would be 3dBs, because there is
vibrating air on both sides of the diaphragm. B&K boast of an
instrumentation mic with 5dB excess noise, but it would be unsuitable for
general use, even if you could afford one.
There is no generally accepted level for weighted thermal noise, so mic
manufacturers often use 0dBSPL as a reference which is virtually meaningles=
s
without a stated weighting.
Without weighting, noise values of the pro quality mics would still look
horrendous on paper because of the 3dB per octave slope, but we use them
happily. In practice, even in quiet locations, You can't hear low level low=
frequency mic noise on a "good" mic. "Mic hiss" is what to listen out for
and you can partly isolate this by my method of putting a mic under a pile=
of bedclothes.
In calm weather I can just hear mic hiss from my old MKH's in my woods. Any=
wind and it is swamped. However I have a de-hiss routine in Audacity which=
works at hiss frequencies only, and is almost undetectable.
Going back to my BBC trainee days, we were told that there was only one
important job to do when recording sound which is to minimise noise, which=
means first recognising what sounds are wanted and what not. Define that an=
d
you are an expert. :-)
David Brinicombe
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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