> Does that mean that their implementation of 24 bit recording is
> better than the others
16 bit recordings give you 15 sequential bits and a parity bit which
doubles the peak to peak of any significant bits, from peak level
sounds to noise. Positive and negative peaks on a meter don't double
up so in practice this means that your dynamic range is 15 bits at
most.
Out of the remaining 15 bits, a digitiser conventionally uses dither,
a low level high frequency random addition to even out the lowest 2 or
3 level steps. In practice, system noise does this in many
"affordable" recorders, but you can check this:
Make a recording with a zero input and amplify it by 13 bits or 78dBs.
Expanding the time scale reveals the individual samples and will make
any dither visible. A "logarithmic" waveform as on Audacity makes this
more easy to see.
What this boils down to is that a 16 bit recording gives at best a 13
bit signal/noise ratio (78db). Where you can't predict the peaks, as
with nature recording, the answer is always to record low, leaving
12dB or even 18dB headroom - two or three bits.
With many recording sources, the natural noise will still usually
swamp the dither, but you will be working at worst with an 11 bit or
66dB dB signal to noise ratio.
With very quiet backgrounds and low noise pro mics and inputs or
mixers, 24 bit recording theoretically gives you another 8 bits, which
is nice but probably difficult to justify. I say "theoretically" as
the dynamic range at 24 bits is 23 times 6dB, or 138dB which is much
greater than any mic input stage could ever come near. With studio
mixers, you don't want to worry about noise, so 24 bit is used, but
with wildlife recordings, this increases file sizes.
Thermal noise of the air is around 0phons (it's frequency dependant)
and the best pro mic systems will have an "excess noise over thermal"
of around 12 dB. Ear damage starts around 90 phons, so if you need to
record this level without adding noise, use 24 bits, but you won't
find a listening setup which can reproduce this range. :-)
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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