Thanks for the responses, this is very helpful. Just to make sure I'm under=
standing all of this, let me know if I have this right. When looking at mic=
rophone-recorder combinations, the noise floor is determined by the noisies=
t element. But when recording natural sounds, the background noise might or=
might not be the determining factor in the noise floor. In a situation lik=
e the aspen leaves, the noise would cover the spectrum and drown out any co=
ntribution of microphone or recorder self noise, so it becomes the determin=
ing factor and a better microphone wouldn't improve the recording. In a sit=
uation where low-frequency sounds are the main contributors to the backgrou=
nd noise, the microphone or recorder self noise would still be heard over t=
he top of this, so a better microphone could potentially improve the record=
ing (if it is the determining factor in the microphone-recorder noise floor=
).
Is that about right?
Thanks,
Bruce
--- In wrote:
>
>
> >> For me, noise masking is an academic dead end. I understand, from the =
principles of 'data reduced' audio storage formats, that there are psychoac=
ustic factors that can be bundled up into theoretical sumations of reproduc=
tion perception.=C2=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 nois=
e.
> >
> >> The fact that there are other noises in the spectrum, doesn't mask any=
thing. It's additive. If an orchestra of "noises" played together, would yo=
u ignore all but the loudest=C2=A0 component ?
> >>
> >> I don't think so.
> >
> > But your ear-brain axis does "think" so. Masking exists as an empirical=
fact. 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=
of
> the recording chain.
>
> Any noise rating requires a defined threshold level in comparison.
>
> The fundamental acoustic noise threshhold level is the noise produced by =
the
> 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 approximat=
ely
> 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 meaningl=
ess
> 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 l=
ow
> 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 pil=
e
> of bedclothes.
>
> In calm weather I can just hear mic hiss from my old MKH's in my woods. A=
ny
> wind and it is swamped. However I have a de-hiss routine in Audacity whic=
h
> 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, whic=
h
> means first recognising what sounds are wanted and what not. Define that =
and
> you are an expert. :-)
>
> David Brinicombe
>
|