[linux-audio-user] (no subject)

Martin McCormick martin at dc.cis.okstate.edu
Mon Apr 12 07:21:33 EDT 2004


Martin McCormick WB5AGZ  Stillwater, OK 
OSU Information Technology Division Network Operations Group
Subject: Re: [linux-audio-user] Fwd: [Jamin] Re: soft clip: Achieving Gain, inconsequential overloads 
--------
Steve Harris writes:
>Actually thats not quite right - AD converters generally work in 1's or
>2's complement, depending on the brand/variety, so the middle point is at
>0, and the range is slightly larger in the -ve voltage range.

	Correct.  We may be talking about the difference between
signed and unsigned number representation.  If you have an unsigned
value, the only possibilities are from 0 to the maximum value
represented by all ones.  There are no negative numbers.  When you
have a signed value, then an 8-bit number, for example can be
represented by +1 to +127 or -1 to -128.

	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.

	This is probably off-topic, but any graphical software that shows
you your music wave forms or does DSP functions in an arithmetic
manner that is based upon an AC model has to behave as if the
mid-point value was 0.

	Maybe someone can set me/us all straight in this manner.
G





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