[M4IF Technotes] mismatch control

[Erik Schlanger]

All,
Some questions on mismatch control:
The implementation of mismatch control in:
MPEG1: touches all of the AC coefficients and works to make the sum of
the AC coefficients odd.
MPEG2 &4: alters only the least significant AC coefficient and works to
make the sum of ALL the coefficients (DC & AC) odd.
I assume that the MPEG2/4 algorithm is superior, it only alters the
least significant coefficient, therefore changing the data as little as
possible. Is this true??? What I really don't understand is what is the
purpose of mismatch control?? Can someone answer this for me and point
me to a reference which explains it?? All i've found is things which
which mention that it is related to controlling long term error in the
IDCT, I don't understand how...
Thanks in advance for you time,
Erik
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Erik M. Schlanger                 
  Alchemy Semiconductor           e-mail : eriks   alchemysemi.com	
   www.alchemysemi.com