--- In Walter Knapp <>
wrote:
> I for one do not care particularly if there is some variation in
part of
> one wave of sound because it has not been shown to be relevant. At
1kHz
> you are talking about a hypothesis of changing a group of just a
few
> cycles with a 4 millisecond timeframe. It's trivia, definitely not
> important to the animals. If it was all that important then the
fact you
> defined each wave with a small number of samples is also
important.
Things would change if you looked at frequencies of 10 kHz.
> I have recorded using some of the finest mics in near ideal
conditions
> using ATRAC. I'm sorry to report, there is still no masking, no
obvious
> errors, not even minor ones of the nature claimed that can be
attributed
> to ATRAC. In fact such conditions are simpler than less ideal
conditions
> with lots of extra noises, so easier to manipulate. The less ideal
> conditions are more challenging, containing much more variation in
> signal. And there is no masking there either. It would be nice to
have a
> switch on a recorder where we could mask out faint background
sounds
> that are unwanted. But ATRAC won't do that.
It seems, that we have another very basic discussion now... ;-)
I agree, that some scientists dealing with bioacoustics should
improve their recording skills. Also, the discussion on ATRAC seems
to be a little bit too emotional. On the other hand, I would always
try to prevent any additional risk, that might arise from the
(potentially) unpredictable behavior of the recording equipment.
Especially as long as I do not know, what I have to expect from the
subjects to be examined.
It is a fact, that ATRAC saves only 20% of the original information
(compared to the CD format and in terms of the amount of data being
saved). This is the reason, why there must be some kind of
degeneration and I suspect that there is no magic involved ;-). This
potential loss of fidelity seems to be not dramatic in many cases
(especially in recordings containing pure-tone signals).
Generally, pure-tone signals do not carry much information.
Theoretically, it would be possible to describe such simple sounds
(e.g. a Canyon Wren song) with a few parameters only (amplitude
envelope and frequency evolution). With very special software (e.g.
the Graphic Synthesizer of Avisoft-SASLab Pro), Canyon Wren songs
could be saved with reasonable quality at a fraction of the
corresponding size of a .wav file (I guess at less than 1%). This is
the reason, why ATRAC would also be able to reproduce such signals
very precise. Almost all available bits can be used to describe that
single pure tone.
Such dramatic, nearly error-free data compression would not be
possible in more complex (noisy) sounds, because there is much more
information to save for a realistic restoration. ATRAC is limited to
a fixed data rate and must therefore reduce the bit-depths for some
frequency bands (those which are less important to the human
auditory system). By theory, this should lead to some kind of
distortion (additional noise or even spurious sounds). Depending on
the kind of signals, this process of reducing bit-depths does not
always lead to dramatic distortions. We can hear this effect when we
shrink a .wav file from 16 bit to 8 bit format (at the expense of
some additional noise).
Unfortunately, I do not own a MiniDisk recorder to run a quick
practical test. I should get one from eBay and do some measurements
using both synthetic and real-world signals. But I will be unable to
show, whether these effects will make a difference to the animals.
That would be much more complicated. I'm sure, that there are
differences between species. A Canyon Wren should definitely accept
a MiniDisk recording. But I would doubt, that it will work for a
some cicadas or grasshoppers...
Raimund
________________________________________________________________________
________________________________________________________________________
|