MOTM

I realize I'm beating a dead horse at this point, but since I 
started a lot of this please allow me to make additional comments.
First of all, Paul is absolutely correct in his Nyquist was a wombat 
comment.
  
The filter is the key to high quality sound and there is no perfect 
filter.  The early designs of these brickwall filter are one of the 
reasons digital had a bad name with some originally.  However the 
filters have improved greatly over the years and oversampling 
improves the situation as well.

Secondly, keeping jitter low is incredibly important.  

Thirdly, it is true that there will be no difference in the 
reproduced square wave, sine wave etc. at 20kHz, either on a scope 
or by ear.  However I would maintain that there is no audible 
difference between a square wave or a sine wave at 20kHz when it is 
generated prior to recording.  The difference is the energy 
contained in the harmonics and since no one can hear the harmonics, 
there is no audible difference.

Fourth, there are no 24 bit converters. You can't get 24 bits 
without cryogenic cooling.  Whenever I hear talk about going to 32 
bits I laugh my ass off.  We'll all need tanks of liquid hydrogen to 
get 32 bits.  However many of the old 16 bit converters were really 
14 bits.  

I run ProTools Mix Plus in my studio with a mixture of Digidesign 
and Apogee converters.  The Apogees sound better.  The reason is 
probably better filters.  Digi wants me to upgrade to HD.  This 
would require a new computer, more drives, different converters, 
different sound cards, a different expansion chassis, a different 
SCSI card, and all upgraded plug-ins (about 100).  Obviously a huge 
expenditure in money and time.  If I was convinced it would sound 
better I would do it.  

If anyone is considering upgrading to a higher sample rate I would 
urge them to spend their money on better mics and better monitors.

End of diatribe.