Boosting frequencies above 2000Hz , & reducing those below 200Hz (on the vocal track only) will make it sound less muffled.
Audacity has a built-in equalizer which can enable you to do that, ( but it doesn’t work in real-time 
There are free equalizer plugins for Audacity [on Windows] which do work in real-time e.g. Very-nice [free] VST plugins from Voxengo - #2 by Trebor