Avid Technology PRO TOOLS MIX 51 - Manual (Page 12)

channel only, you should use the
LFE panner plug-in.
Default/Fine-Tune
Opt-click (OS X) or alt-click (WinXP)
to reset any control to the default
position. Hold down the cmd key (OS
X) or the control key (WinXP) to
perform fine-tuned adjustments.