"Self noise" is difficult to understand in a "practical" way. You can
"practically" tell that 23dbA is noisier than 16dbA, but two mic=B4s
which both truly measures 16dbA might make you "hear" two very
different noise levels.
It is not only that self noise have different spectrums, but also a
psychoacoustical effect.
I have used the same capsules, with the same "self noise", in all my
experiments with boundary rigs. No EQ. But because of what the
background / atmo sounds like, depending on the rig, they "make" more
or less "self noise".
Put simply: With lots of aspens around, and boundary side/side
effect, you will hear no "self noise" at all...
But it is much more subtle than that. It is more subtle than "masking" eve=
n.
It is more like.... some character in the
background/atmo/stereo-effect will "catch your attention", not
"hearing" other things. It is not the same as "being subjective" it
is more neurological than that.
I would be surprised if there were not people on this list, able to
explain it better.
Klas.
At 01:09 2012-04-02, you wrote:
> > Given microphone specs typically include either self-noise or SNR
> > figures, though never that I have noticed "excess noise" figures,
> > for practical purposes how do we determine excess noise?
>
>John,
>
>As I am a Sennheiser fan, I'll name them as quoting excess noise
>figures. It is also used by B&K for their instrumentation mics which
>incidentally, despite their price, are not necessarily good recording
>mics. It is also a BBC Engineeering parameter. Thermal noise rises at
>3dB per octave and so sounds as hiss and also really needs the 468
>noise weighting. This however looks worse than the A-weighted figure
>which is thus used for non-technical sales, but this peaks in the
>lower KHz where the ear is less sensitive to low level noise.
>
>If you look at a power spectrum of mic noise, you can sometimes see an
>HF tip-up of 3dB per octave in the higher KHz. That is thermal noise
>but not necessarily air thermal noise. While I'm being nerdy, the
>absolute bottom limit of excess noise is 3dBs caused by air molecules
>on both sides of the diaphragm. B&K claim a World record of 5DB.
>Sennheiser claim around 23 dBs which includes a 468 weighting lift of
>11 dBs making the absolute thermal excess noise about 12dBs. Their low
>frequency absolute "self noise" is higher but in practice is less
>noticeble.
>
> > for practical purposes how do we determine excess noise? What do
> > these figures look like when included on a spec sheet, how do we use
> > them to determine the qualities of a mic compared to using
> > self-noise figures?
>
>I can't quote the exact figure for the thermal noise of air off hand,
>but at 10 kHz it is near 0phons (20 microPascals SPL). Most people
>cannot hear it but I claim to have heard it in my youth. :-) Excess
>noise is simply the microphone "self noise" level in reference to this
>fundamental point. The problem with "self noise figures" is that they
>don't state a direct reference level and also use loud-sound
>A-weighting. A quoted signal-to-noise ratio for a microphone is even
>more nebulous.
>
>Upsum for all of the above - beware of any noise figure and rely on
>your ears. :-)
>
>David
>
>David Brinicombe
>North Devon, UK
>Cogito cogito ergo cogito sum - Ambrose Bierce
>
>
>
>------------------------------------
>
>"While a picture is worth a thousand words, a
>sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
>
>Yahoo! Groups Links
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
website: www.telinga.com
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