--- In Walter Knapp <>
wrote:
>> I did not change the gain between the two examples. Also, the
>> spectrogram contrast was not changed.=A0=A0
>However it was a simple matter to measure that. Overall your mp3
sample
>is boosted about 1dB over the original. Not uncommon for mp3
encoders to
>give a different level slightly. I did not dissect it on a sample by
>sample basis, probably even greater errors in that. Visually I
could see
>the differences in the overall waveform display switching back and
forth
>between the two samples.
Ok, that might be true. But as you say, this 1dB difference is
caused by the encoding / decoding process itself. 1 dB is almost
nothing and can surely be neglected.
>> Such sharp transients are often present in animal sounds (e.g.
some
>> song birds or grasshoppers). There is no clippng involved! At
least
>> not at the upper edge of the dynamic range. But there is of
course
>> some kind of clipping at the bottom edge of the dynamic range.
This
>> is the 'magic' behind the both the ATRAC and MP3 systems.
Hopefully,
>> would will understand this correctly.
>Look at it expanded out enough too look at the waveform of the
original
>you will find quite a few notched peaks, a common form of clipping
>artifact. I know it's not true clipping, but has the same waveform.
>Sharply notched peaks are virtually a unknown in natural
recordings. And
>I have looked at the sharp transients of animals of all types. The
ones
>I'm talking about are single sample notches and are very common in
this
>original. You also have sample variations throughout where it's
runing a
>intersample transition from full minus signal to full plus. Real
natural
>environments don't have that kind of high frequency content.
Yes, I simply deleted some short sections of the synthesized sounds
in order to see how these short beaks will be transmitted by the
system. If you record some bird songs at close distances, you will
see similar effects in real-world recordings (of course not so
extreme). Look at some of my own recordings of the Goldcrest or the
Fan-tailed Warbler:
www.avisoft-saslab.com/sounds/sounds.htm
By the way, these extremely sharp on-sets of the synthetic test
signal are reproduced surprisingly well by MP3. Things might get
worse, if you had a longer series of such short sound elements.
Then, the bit reservoir feature of MP3 (a very clever trick to
improve the quality of short complex sound events) might reach its
limitations. So, your argument regarding the extremely sharp
transients does not count...
>> The original test file was generated using a flexible sine
generator
>> (and noise generator). That special software can also be used to
>> generate very naturalistic animal sounds. Download the demo
version
>> of Avisoft-SASLab Pro from:
>>
>> www.avisoft.info/downloa_.htm (first item)
>If this was a example of it's naturalistic sound, no thanks. I've
never
>seen such a consistently crummy waveform out of a nature recording,
even
>those with clipping. Like sonograms, I also look at the waveforms
of my
>recordings. The most common thing for me to find when I hear some
error
>in a recording is a few wavetops with clipping. Even crude redraws
of
>those will generally remove the problem. Tedious work, so I try to
avoid
>the need. But, for a rare recording I'll do it.
You misunderstand this at all. Perhaps, my English is not the best
(my native language is German) and therefore, this might be the
reason for this miscommunication. Generally, it is a commonly
accepted scientific procedure to use very simple signals to explore
a black box system. This will make things much easier to understand.
If you like more natural synthesized sounds, look at the
spectrograms at:
www.avisoft-saslab.com/pro_.htm
Scroll down to the Synthesizer section and look at the spectrogram
of a re-synthesized part of a Nightingale song (the synthesizer was
controlled by parameters extracted from a natural song) or even at
the modified penguin calls below.
>I have a pc here as well. But, as I said this sure did not look
like it
>was doing anything I had a need for. There are mac signal generators
>that generate good signals.
I'm afraid, that these tools are unable to generate such complex and
naturalistic sounds by simple mouse drawing ...
=20=20=20
>I should note it's fairly trivial to filter out those artifacts you
are
>so worried about. Use a dynamic range filter on most of it, should
work.
>Anyway, looks removable that way. In nature recording it would just
be
>part of the background noise people were filtering. And a minor
part at
>that as it's not audible.
It is not trivial (I should say impossible) to filter out a noise
tail, that surrounds complex sound elements (e.g. the zig-zag shaped
structures in my test file). It is true, that similar effects can be
caused by reverberation in real-world recordings (echoes from many
different reflective surfaces at different distances =96 e.g. the
leaves in a forest). But, you, with your excellent recording skills,
would be able to minimize these effects by getting closer or by
using a parabola. Unfortunately, you can not switch off the noise
tails caused by the ATRAC system. Instead, you should use a
different recording system without compression. Even an analog tape
recorder would be more appropriate in some situations. Of course,
you had to struggle with tape hiss and tape speed variations, but
these effects might be less critical for many applications than the
spurious noise introduced by ATRAC!
A dynamic range filter is a very poor tool. Actually, you will
reduce the dynamic range of your recordings dramatically. Soft
sounds buried by the ATRAC noise will get lost completely. At the
end you had a sound file with a resolution corresponding to a 4-bit
wave file (considering the spurious noise of -28 dB introduced by
the compression system at the worst case)!=20
So, I do not understand why you demand 16 or even 24 bit resolution
while your ATRAC system degrades the resolution at the worst case
down to something like 4 bit only??? All the high-end microphones
and pre-amplifiers would be wasting money. Ok, you can benefit from
their good properties at most parts of a recording, but some
critical sections will be extremely degraded.=20
I would accept the ATRAC system, if there were no alternatives. But
there are affordable alternatives. I also agree, that the MiniDisk
devices have their own appealing advantages. So, you have to decide
which of these compromises are acceptable to you. MiniDisk would be
not a satisfying option for me, because I'm always interested in
spectrographic analysis...
Raimund
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