Raimund Specht wrote:
> Things would change if you looked at frequencies of 10 kHz.
unlikely, I've looked at how many wave cycles constitute even a small
part of a call. That's your big problem, you are analyzing so fine you
have lost sight of the question. Which is animal response.
And then you are back into that area where our sonograms are showing
what's going on.
>
>>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'll bet if someone invents such a switch it will sell very well indeed.
For now all we can do is try through directional mics or mic choices to
not pick up the unwanted stuff. Or spend hours filtering it out
afterwards, if possible.
> 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.
I agree, the detractors of ATRAC seem to be running on emotion, not facts.
ATRAC is very, very predictable. It's a fixed circuit on a chip, will
respond exactly the same way every time. If you want unpredictable, go
to DAT tape, which is considered to be so perfect. I went to MD for it's
predictability.
> 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).
This is where your inexperience with ATRAC shows. ATRAC saves none of
the original information. Understand that exactly, so I'll repeat it,
ATRAC saves none of the original information. What it saves amounts to
instructions to a synthesizer. This is one of the big errors made in
understanding ATRAC, making the simplistic assumption that it tosses 4
out of 5 samples. If that's all it did, no matter how intelligently, it
would not be likely to do very well. As we know from midi extremely
small amounts of data fed to a synthesizer can produce extremely complex
sounds.
> 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).
Again, you need more experience in the practical side of using
compressed recording. I don't make a blanket assumption that ATRAC won't
be able to handle complex sound accurately. Because I have used it on
just such sounds and analyzed the results. For many years now. I'm still
looking for a repeatable case where it fails in nature recording.
Every digital recording method is limited to a fixed data rate. What
that data rate is used for is quite different however.
It's also unwise to think that ATRAC chooses which bit depth to reduce
based on human auditory systems. Nearly all of that it does is based on
things like waveform shapes, not the much brought out human hearing. It
chooses bit depths based on how easily the shape can be described. It
assigns more data to more complex parts. Will it limit out doing this?
Yes it should eventually. But long after CD, which has the same sampling
rate, but applies it evenly no matter if needed or not. Or DAT, which
also is dumb sampling, no choosing. Both of those waste a lot of the
bandwidth they have.
> 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...
The common characteristic of those giving great expositions on how ATRAC
messes up is that they have nearly always never tried it for any
extended period, never done careful analysis of it. The few that have
used one have almost always used a consumer walkman MD, and virtually
all they attribute to ATRAC is actually some other part of the machine.
No one should be surprised when a consumer recorder costing a few
hundred dollars does not record as well as some pro recorder costing a
thousand or more.
I will tell you right up front that separating ATRAC from all else
that's going on in the machine is not a trivial task. Best I managed was
when I provided this list with a small blind listening test. I've looked
at the attempts of others, most of which also had flaws. To claim that
ATRAC did it, you have to isolate ATRAC.
Since some insects go into the ultrasonic, I'm quite sure MD won't do
for them. And not too good at bats, though I have heard bat calls
recorded on MD. Ones within it's frequency range.
You should be aware that for many years tour guides who use playback
have mostly gone to MD. It works fine for them, and their income depends
on keeping the clients happy. I doubt that they stick with calling
simple callers.
Walt
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