> Olympus LS-10 http://www.avisoft.com/LS-10.pdf, LS-11 http://www.avisoft.=
com/LS-11.pdf(SENSE LOW, LEVEL 10, 24 bit) -121dBu
>
> Olympus LS-10 http://www.avisoft.com/LS-10.pdf, LS-11 http://www.avisoft.=
com/LS-11.pdf (SENSE LOW, LEVEL 10, 16 bit) -113dBu
>
> David, you have a wealth of experience and knowledge, so I ask you:
> what is the point of these measures?
Marco,
I've had a rummage through the specs, and these quotes seem to be input
specs without an input device, but probably using a 2KOhm input impedance t=
o
match the mics. It's difficult to tell.
The question is what difference the bit rate makes using the built in mics=
or a matching external 2KOhm mic. I would assume that these figures were
done with 2K "dummy load" inputs. What I can't find is noise figures using=
the mics.
Theoretically the difference between 16 and 24 bit recording is 48dB, but
you won't get anything like that it real life. Where you do benefit
marginally with 24 bit is in losing the 16 bit "dither" added to the bottom=
three bits to make the quietist bits of a recording less crunchy. Losing
dither can theoretically give up to 18 dBs less "noise" in a perfect system=
.
With wildlife recording, HF hiss is an annoying background noise but
unfortunately, noise figures use A-weighing which filters out the hiss,
reducing the value of noise specs. As ever, the ears are the ultimate test.=
I use the pile of bedclothes test for system and mic noise. Filter out the=
lower frequencies and look at the hiss on a power spectrum. That way you ca=
n
compare built in mics with external mics.
In practice, outdoors is usually quite noisy unless you are close to the
source of sound. Wind and man-made noise produces low frequency noise but
this can often be filtered carefully without destroying the wildlife
element. Tree leaves can be quite noisy at HF, but as the distance
increases, air absorption filters out the higher frequencies, exposing the=
mic and recorder HF noise. HF air absorption is why distant thunder rumbles=
and close thunder crackles.
The benefit of the pile of bedclothes test is knowing what the mic plus
recorder HF noise sounds like. Very often, natural outdoor noises will swam=
p
this anyway. Even with 16 bits, the digital noise will normally be well
below other HF noises, so it is safe to record low, well below any peaks yo=
u
can expect.
The ultimate test is to record the same scene at 16 and 24 bit to hear what=
the difference sounds like. That is what counts, not laboratory
specifications.
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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