audio playback during processor intense activity

[Aaron Peterson]

I have a Dell workstation with dual P3 933 Xeons, 256M ECC RDRAM, 2 18G
Ultra160 SCSI drives.  It is loaded with FreeBSD 4.9, and the only thing
I've changed about the kernel configuration is the 2 options to turn on
SMP capability.  During processor intensive activities like encoding mpeg4
from dvd with mencoder, xmms audio playback frequently "jitters" for lack
of a better term.  I never experienced this with my 2.4GHz Celeron
machine, with normal pc hardware (DDR, ATA disk, etc).  I'm wondering if
there's something I can tweak, perhaps with sysctl, that will improve my
situation.  I was under the impression that a dual cpu would load balance
processor usage better, and at the very least i could run mencoder on one
processor and everything else on the other.  Is this likely to be caused
by some other system hardware?  I'm using a Sound Blaster Live card, which
I think should be well supported by now and is not a bottom of the line
sound card.

As a side note, it is interesting to me that when watching top, the
mencoder xmms processes (as well as all the other processes) seem to jump
back and forth between processors.  Why would they do that?  So sometimes
xmms and mencoder end up on the same processor...  I'm sure I will see
this problem with other applications as well, this is just my real world
situation at the moment...

Aaron