12 Apr
2004
12 Apr
'04
2:59 p.m.
On Mon, 2004-04-12 at 09:27, Steve Harris wrote:
On Mon, Apr 12, 2004 at 06:21:33AM -0500, Martin
McCormick wrote:
Steve,
I wonder if you have any info on something I was reading in Bob
Katz's book recently, that many A/D converters actually have compressors
or other sorts of non-linear circuits built into them which effect the
use of the converter when it gets anywhere near maximum value anyway.
I found some of his comments about what happens with A/D's in these
regions interesting. Do the spec sheets you've looked at imply anything
like this?
Thanks,
Mark
Now, here is something I am a bit unsure of,
myself. I know,
from actual observations that a straight PCM output from your basic
A/D converter if read as unsigned numbers moves in steps from 0 to all
1's on. I honestly have not tried to interpret those data as signed
numbers because it wasn't convenient at the time. If one wants to
have a valid representation of what the wave form is doing for
graphical or calculation purposes, then the mid-point would have to be
what one would call 0 level with -1 being one below and 1 being 1
above, etc. I am certainly not arguing with anyone, but am a wee bit
confused as to the correct way to represent the numbers.
Audio AD converters are asymmetrical - abs(minimum_voltage) is higher than
maximum_voltage. Audio AD converters sometimes have unsigned modes, but
they seem to have different behaviour. I checked up recently to make sure
JACK was doing the right thing(TM) when converting between floats and
ints. This stuff is explained in detail in the AD converter spec sheets
for the AD converters uned in the m-audio delta cards.