> Just to be picky, mv/Pa cannot be "converted" to dB
But some manufacturers give their sensitivity specifications in mV/Pa but s=
ome in dBu (which is really dBu/Pa), and some in dBV (which is really dBV/P=
a, although sometimes it is dBV/0.1Pa just to confuse us). And sometimes th=
ey just give a number and don't say what it is!
My formulas simply convert among mV, dBu and dBV. That is what I meant. I a=
pologize for not being clearer about that.
Decibels are a tad confusing to begin with since they are not an absolute v=
alue but a relative value that must reference a known quantity. And it gets=
still more confusing when we are talking about sound in air or in water, w=
here 0 dB SPL is either 20 micropascals (air) or 1 micropascal (water). I d=
on't blame anyone for being confused. I'm not 100% sure that I am not!
And then the manufacturers confuse things further by obfuscating their spec=
ifications to make their products look better.
But still, many mics have specs in mV/Pa for sensitivity and dB SPL for sel=
f noise (or s/n in dB), and I have found that these numbers do have real wo=
rld value. I have tested all of my mics and preamps and they all conform to=
the specs within a reasonable margin (especially considering I do not own =
any fancy test equipment and depend heavily on Audacity and my ears to eval=
uate different mic/preamp combinations).
All of this has helped me make choices, so I think it is not a useless purs=
uit.
But then, after all the calculations I have made and testing I have done I =
am not sure that I am 100% sane any more. Maybe it's just something to do i=
n the dead of winter when there is nothing to record but more brittle wind.
John
--- In "Avocet" <> wrote:
>
> > I have many other formulas for converting dB to mV/Pa and converting
> > between dBV and dBu for example, but these are the two I have been
> > using a lot to educate myself about how these parameters interact.
>
> Just to be picky, mv/Pa cannot be "converted" to dB, but you can refer
> it to phons at 1KHz as 2Pa SPL corresponds to 100phons (1Pa is
> 94phons) unweighted. We can't hear 0phons so that is only a
> theoretical reference. NB the phon is what we hear but is only defined
> at 1KHz.
>
> Noise figures are the most difficult to pin down as there isn't a
> simple quotable fundamental noise level to refer to without quoting
> weighting. The fundamental thermal air noise is proportionate to
> frequency at the rate of 3dB per octave, so any noise level has to be
> against a weighted reference. Thermal noise at exactly 1kHz is 0Pa SPL
> or -infinity phons as the bandwidth is zero. See the problem?
>
> Manufacturers like to use A-weighting as it gives better figures, but
> the best weighting is ITU-R 468 which actually corresponds to what we
> hear at low levels.
>
> EIN figures are referred to (generally) A-weighted thermal noise, but
> I suspect that some are referred to 0phons or 20microPascals at 1KHz
> which is not the same thing and the wrong frequency.
>
> I was taught that "dBm" was the reading on a meter, specifically a VU
> averaging meter, referred to 0.775 volts RMS sine wave. Most sounds we
> record are not sine wave, and most meters now are peak reading, but we
> can forget the difference in practice, but it does mean a few dB
> difference in relative noise levels. Audacity shows both in the
> waveform display. If you want to be really confused about various
> decibels, read Wiki. It needs rewriting.
>
> As an aside, compression raises the average level compared with the
> peak level and is used to make adverts sound louder.
>
> What really matters is what a mic sounds like to our ears, and specs
> are a guide, but not a reliable rule to go by. The beleivability of
> noise figures is dependant on the price bracket.
>
> David
>
> David Brinicombe
> North Devon, UK
> Cogito cogito ergo cogito sum - Ambrose Bierce
>
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