[naturerecordists] writes:
> Is 24bit 192kHz good enough or is there too much valuable info above 90kH=
z that wouldn't get recorded
It all depends on how you are going to analyse the calls later. To hear the=
m
you can slow them down or, as with bats, shift the frequencies
arithmetically downwards by heterodyning them.
A likely reason for dolphins using ultrasound for navigation and prey
searching is that sound travels about four times faster in water than in
air, so to get better definition they have to raise the frequency.
With bats, their prime echolocation is believed to use the fundamental call=
frequency rather than the harmonics, if only because of the rapidly rising=
absorption of higher frequencies by the air. I don't have figures for
absorption in water, but this study would need a higher sampling rate.
24 bits would very likely not be necessary as 16 bits give a large signal t=
o
noise ratio anyway. The parity bit plus 15 bits gives you a theoretical
range of 90dB. Almost nothing is that quiet to warrant a higher bit rate.
I would expect the limiting factor would be the hydrophone, not the
recording system, but it may be useful to record at higher sample rates if=
you were doing research into the higher harmonics above 90KHz. For due
process, you would also need a calibrated underwater sound source so you
could do HF absorption measurements.
I'm assuming with all the above that the dolphins are in free water. If the=
y
are in tanks, you will have multiple echoes to contend with.
David Brinicombe
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