I think he is refering to Scribe Bound, a bound that I doubt anyone has beaten.
ADDITION:
I think he/she get the music to loop so loudly that the background noise from the units being killed seemed to be muted, when in fact, its what this guy aid:
QUOTE(O)FaRTy1billion @ May 7 2005, 11:18 AM)
("Mute Unit Speech" only mutes speech, and sets rest to 1/2 volume, except triggered sounds)
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... (but I could be wrong, again).