--- In Walter Knapp <>
wrote:
>I've been waiting for 7 years for someone to actually show these
effects
>that are so far just imaginary, nothing more than a hypothesis. I
have
>done considerable looking on my own as well, I'm a scientist. It's
time
>someone put up or shut up. All we have had is Cornell trying to
pass off
>digital clipping as the effect of ATRAC. Still trying to pass it
off as
>the effect of ATRAC today on their website. That's how frantic some
are
>to discredit ATRAC. I don't understand this sillyness, it's
definitely
>not scientific. A scientist knows that his hypothesis must be
tested or
>it's nothing. A scientist provides real data and shows how that's
relevant.
>So, do it, show us, and demonstrate how it makes a difference to the
>animals. I've done every resolution of sonogram available to me
without
>finding what you talk of. ...
Walt, I have just prepared a quick comparison of both uncompressed
and compressed digital audio as you suggested:
http://www.avisoft-saslab.com/compression/compression.htm
I guess, that you will argue, that these tests were made with MP3
and not with the latest ATRAC system. However, I will NOT buy one of
these expensive MiniDisk machines. The underlaying principles are
always the same. The improvements may lead to better listening
pleasure, but the loss of data will remain.
>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.
Not true! There seem to be dramatic differences between the various
versions of ATRAC. Each version may encode differently. This is
because the ATRAC system does not demand a unified compression
regime. It is up to the manufacturer to implement different psycho-
acoustic models. Also, the more sophisticated versions as MP3 with
its 'bit reservoir' feature will add even more irregular effects.
>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.
I'm sorry, but I would wish, that you improved your reading skills...
I did not say that there would be a simple sample rate reduction of
5:1 !!! But of course, that would be one way to reduce the data
rate. For instance, you could use 8 bit instead of 16 bit and a
sample rate of 22.05 kHz instead of 44.1 kHz, That would provide a
data reduction of 4:1 and the results might be not too ugly for
noisy nature recordings.
There is no pure synthesizer in ATRAC. The time-domain data are
transformed into the frequency domain and the resolution of these
data (which correspond to the time domain data) is reduced in order
to shrink the data stream. These frequency domain representation of
the signal is saved onto the disk. The decoder transforms these data
back into the time-domain (using DCT, something similar to FFT).
I say it AGAIN, I do NOT argue, that ATRAC or any other compression
technology is bad for the purpose it was designed for (human
listening). But you should know the limitations (we already leard
this on parabolas...) when you use that technology for research in
animal sound communication.
>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.
That's definitely false. Follow the links to the description of
ATRAC I submitted on my website and you will see what is really
going on. You are mixing some truth with a lot of fairytales. I'm an
engineer and have some experience with digital signal processing.
Even if I have not used ATRAC much, I can explain, what's going on
(after reading the technical specifications).
I'm very sorry to say all this so clearly, but I just want to
prevent that others become confused about the truth on data
compression technology.
I'm a little bit tired of discussing these things in that way. Make
your own experiments with a clean test signal and you will
understand what I mean.
Regards,
Raimund
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