jbensh wrote:
> One of the ways i am trying to learn about itjaritjari is to listen
> for them using grids of geophones. Everything itjaritjari do
> underground makes some sound/vibration, and its a good bet that they
> use the sounds of other animals to hunt them too as internally their
> ears are well developed. We have heard itjaritjari a few times, but
> the catch is that one often has to wait a long time before an
> itjaritjari comes along. Currently, we are still doing the listening
> manually, but we have been building semi-automatic system that will
> go on and off at predetermined times. This system will be controlled
> by a computer and record from up to 32 geophone channels
> simultaneously (effectively) so we should be able to triangulate and
> track the animals too.
>
>
> Amongst all this I need to be able to make good quality recordings of
> what we hear in the geophone grids (itjaritjari moving and
> vocalising, insect and other potential food noises, etc). I have
> been using a nagra 1/4" tape deck, but its an awkward medium and
> inconvenient. I have been looking at some of the pros and cons of
> replacing this with digital, but I can't really afford a DAT. So I'm
> trying to decide between a portable minidisc recorder or something
> like the nomad jukebox 3. However, I am a little wary of minidisc
> because the compression is lossy and may miss more subtle parts of a
> signal. In this regard recording undergrounds sounds as WAV files is
> probably an advantage, which the jukebox does. The jukebox with 20
> or 40Gb would also provide a means to download the geophone computer
> in the field, and is also attractive from the point of view that it
> would be easier to protect from sand in the field and boasts a 98db
> signal-noise ratio.
You are making far too much of that word lossy. ATRAC loses data size,
but it's extremely hard to find where it lost data. About the only area
where any consistent change can be found is right up at the highest
frequencies. It fairly consistently will loose some of the sound there,
the sound that's 50dB or more below the primary sound at that frequency
will be attenuated. This in the top few khz of the frequency range.
Since this is usually electronic or mic noise it's not a big problem.
Other than that, everything will be in the recording, the fine details
and all. It does not store any of the original data, stores more like
instructions to the decoder as to how to reproduce the original. And
it's extremely good at it.
You will not avoid compression, it's throughout your computer system,
you only know about a small part of it, it's not a bad word, it's mostly
done extremely well.
Working off geophones, I doubt you have anything like a 98dB dynamic
range. Even working off high quality mics directly most nature recording
only yields a few tens of dB range. You are used to the specs of analog
recording. In digital nearly everything can do these high ranges. Except
what we are recording. In theory a ATRAC encoded audio will have a
larger dynamic range than is possible with fixed, 16bit audio like .wav.
It does both bit shifting and variable bit allocation to do this. The
most recent ATRAC is more like 24bit in this regard.
I don't see any particular advantage of recording .wav over minidisc.
The quality of the recording will be determined by your front end, the
geophones and associated electronics. Certainly against analog tape
it's not a problem.
Minidisc is a very durable field format. It's been used in the reporting
environment in war zones for long periods without failure. It's hard to
imagine more abuse for a recorder. The recording on a minidisc has a
life expectancy that's archival. I would trust it over a HD system for
field work.
If your grid is already being interpreted by computer, why not just save
the audio there and avoid a separate recorder? The software to do that
should be no problem. This is the sort of method the new Cornell
recording units do. The onboard computer manages sampling timing, and
records as well. All just a set of boards wrapped around a hard disk.
Interface for setting, etc. is a notebook computer. Unfortunately they
don't sell theirs, and have not published info so someone could easily
duplicate it.
I'm not sure about the durability of a consumer mp3 player like the
nomad under field conditions in the outback. That's way outside of it's
design parameters. There are certainly minidisc recorders designed for
field work, like the HHb Portadisc I use. Note I would not consider the
Portadisc a good choice for unattended recording, it would be too costly
for that sort of use. A simplified, purpose designed recorder would make
a lot more sense.
Walt
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