[linux-audio-user] (no subject)

Mark Knecht markknecht at comcast.net
Mon Apr 12 12:53:06 EDT 2004

On Mon, 2004-04-12 at 09:27, Steve Harris wrote:
> On Mon, Apr 12, 2004 at 06:21:33AM -0500, Martin McCormick wrote:
> > 	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.

   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?


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