Walt wrote:
>ATRAC's bit depth reduction will occur mostly in those thousands of sample=
s in
>between each pulse, we don't need full bit depth to characterize silence
I do believe this could be true from side by side experiences with MD
and DAT using same mics, pres. For ambient recordings or those of a
number of sound sources at a distance (not one, foregrounded call)
there seems to be some acoustic detail that's lost with MD/ATRAC
scheme. For example, long reverb tails that aren't there on the MD
recording. When I try to coax more out of the low level MD recordings
with careful eq, its evident there's more garbage than on the DAT.
I'm also wondering if low saturation/saved bits could be part of
Aaron's discrepancies. Saturation seems to be a critical variable,
also the quality of D->A and monitoring people are using when making
the judgements. Rob D.
the whole string:
>Raimund Specht wrote:
>
>> In fact, the compression is achieved by reducing the bit-depth in
>> some frequency bands. This is an adaptive process that is controlled
>> by the properties of the sound being recorded (and the properties of
>> the human auditory system). If the bandwidth of the incoming signal
>> is limited (lets say below 8 kHz), the compression will have little
>> effect on the sound quality (even in more complex sounds). However,
>> if there are larger signal bandwidths (or rapid frequency
>> modulations over large frequency ranges), the compression will lead
>> to some degeneration. This would explain why low-frequency impulsive
>> frog calls are less affected than higher pitched bird or insect
>> sounds. The example posted by Jeremy is a nice illustration, how
>> rapid frequency attacks with larger bandwidths may lead to serious
>> distortion.
>
>I think we should all note that Raimund does not own MD and has no
>experience recording with MD. His "tests" of ATRAC did not test ATRAC,
>but another entirely different compression type. In other words he's a
>complete novice in what MD does.
>
>This is a deliberately oversimplified description of what ATRAC
>compression does, to the point of being highly misleading. I will not
>attempt here to describe all it does, but just attempt a little
>correction. I do not claim to know all the details of it's internal
>operation, I expect no one except the experts at Sony really know all it
>does and why.
>
>Bit depth reduction is not applied evenly in ATRAC, it's applied where
>it won't show, won't produce artifacts. There are vast amounts of a
>recording where this can take place. There are huge amounts of redundant
>data in a digital sound recording.
>
>Let's take, for instance, the case of the Marsh Frog recently brought
>up. The internal pulse structure of the call I described, for 1/10 of a
>second there is sound to describe, then there is a space of nearly equal
>length in which no sound occurs, followed by another pulse. ATRAC's bit
>depth reduction will occur mostly in those thousands of samples in
>between each pulse, we don't need full bit depth to characterize
>silence. And we have not even gotten into the space between each call
>where there are thousands and thousands of samples that don't differ one
>to the next. Virtually all of ATRAC's compression is achieved by such
>simple methods, not the elaborations supposed by some. But it can also
>work where there is sound, where the shape of the curve is following a
>simple path it often needs little to describe the difference from one
>sample to the next. And it can handle a considerable load of highly
>complex sounds.
>
>In natural sounds as opposed to test samples deliberately constructed to
> use up ATRAC's abilities, complex multi-frequency transitions are of
>very short duration, not continuous, they occupy a minor part of the
>recording length, almost insignificant. ATRAC incorporates special
>discrimination to detect such short pieces and up it's bit usage to
>cover them. It uses more of it's store of bits when it needs to, in
>other words. For the vast majority of the time in the recording nothing
>much is happening. That's where it saves bits and gets very tight on bit
>depth. It's really constructed to preserve the sound information, not
>bits. They are definitely not one and the same.
>
>> I agree, that ATRAC does not add 'filler' noise in order to mask
>> artifacts. However, the encoder itself will introduce some kind of
>> white noise. This is a (unwanted and system-inherent) result of the
>> reduced bit-depths (also called quantization noise). This kind of
>> noise is clearly visible in Jeremy's recording at t=3D6,3 sec:
>> http://www.avisoft-saslab.com/compression/MDtest2MD.gif
>
>It is well to remember that the analysis software being used does much
>the same thing as compression, in fact it's really extremely severe and
>crude compression of the sample then displayed as a visual image. It
>produces it's own artifacts, some of which Raimond misinterprets as
>being in the sample. It takes time and experience to learn to interpret
>the fine details of sonograms.
>
>I see no consistent white noise generation in ATRAC encoded material.
>And I have been using and analyzing it for many years. If it were system
>inherent, it would be very consistent, we are talking about a fixed
>piece of circuitry. We would always see such generation regardless of
>the material. Not just a spot here and there. That did not necessarily
>repeat. Scientific investigation demands reproducibility, and that's
>what's been lacking. One recording we may be able to demonstrate
>something, then the next recording that has material of the same type
>won't have it. Try it, record for a few years, analyzing everything. The
>longer you go, the less sure you are going to be of the effects of
>ATRAC. That's why the most sure folks about the bad effects of ATRAC are
>those with no experience using it in actual field recording.
>
>Walt
>
>
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