At 3:22 PM -0400 7/27/04, Walter Knapp wrote:
>From: Rob Danielson <>
>
>> Mic, mic pre quality (low noise and low harmonic distortion
>> particularly) and favorable A-D characteristics ("quality" vs low
>> price ) do seem to be larger factors than 16 vs.24 bit recording
>> resolution, but I'm not sure my experience bears out Pohlmann's
>> assertion that field resolution is effectively maximized close to the
>> performance of 16 bits (if I understand this correctly). I've had a
>> half dozen experiences with bringing home both 16 and 24 bit files
>> from the same location through the same front end. It's easier to
>> work with the 24 bit files compared to the 16 bit files. There's more
>> "body" providing more subtle tonal/amplitude differentiation making
>> equalization changes easier and more effective. The lower the file
>> saturations, the more pronounced the difference. I do up-sample 16
>> bit recordings to 24 bits in post when I know they will go through
>> further changes downstream, but this does not create a file that
>> handles as well as a 24 bit orig. All plugs are converting/working
>> with 32 bit floating regardless of orig sample rate of course. Maybe
>> there are better A-D units/methods out there today than Pohlmann was
>> basing his analysis on. It looks like the 4th edition was printed in
>> 2000. Rob D.
>
>You have misread what I put up of Pohlmann's info. He states a limit of
>20 bit resolution, which is 4 bits better than 16 bit. So, there would
>be differences if using a 24 bit, just not 24 bits worth of difference.
>
>I have strong doubts anyone has gotten around this point of Pohlmann's.
>It's based only on the voltage difference involved in a 24 bit
>resolution compared to the inherent thermal noise voltage variation of
>resistors. The damage occurs in the filters on the analog half of the
>A/D that are part of the A/D process. That voltage variation will exceed
>the step voltage, wiping out the fine step's accuracy.
>
>My read out of what he says is that only the high quality 24bit chips
>will get the full 20 bit resolution. So, cheap 24 bit recorders will
>probably exhibit lower quality in this regard than good ones. And even
>the good ones the resolution limit will be somewhere around 20 bit. And,
>of course, any higher bit recorders will be pure hype. Even now, a cheap
>24 bit recorder may not be giving a significant gain over a quality 16 bit=
.
>
>The way around this limit is complex. He discusses other A/D designs
>than straight linear, and also discusses their noise problems too. I
>believe that, based on what I've read, farther increases in digital
>accuracy will have to come from moving away from linear. Go to targeted
>systems where the accuracy is distributed more like it's needed. It
>will, of course, require getting around those fine voltages to do it.
>
>Walt
>
>
Thanks for the clariication and patience. And the ~4 bit improvement
is most audible when one is able to play back the 24 bit files on
high quality D-A converters-- which very few can do today. I am
impressed by the investments some people are making towards speakers
though! Rob D.
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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