Nobody wants muddy, stuffy tone. Luckily with the Parametric EQ in the Eleven Rack, you will have no problem dialing OUT the mud, and dialing IN the awesome.
First off I should mention that the Parametric EQ was added by the Eleven Rack Expansion Pack, which now comes standard with new Eleven Rack Bundles that include Pro Tools 9 and up.
So what is the "mud range"? Well, it matters who you ask. Broadly you can say that you may build up some nasty mud in the range of 160 - 500 Hz. Now that does not mean to run out and remove all dB from those ranges. Its just a general out line of where the muddiness 'may' lie for that track, or Rig, ect....
You want to be careful when removing dB from the upper ends of the broadly defined mud range above. If you remove too much of the low mids and mids, you will rob your guitar of the frequencies it was meant to fill - the Mid Range. Now of course there may be times when you are looking for a scooped tone, but if you are not, then take care not to remove wide bandwidths of low and upper mids. This is also not to say you cannot remove Mids, if you tighten up your Q and take out smaller slices in the Mid Range, then that could work very well.
Where I look for the Mud Range is between 160 - 320 Hz, depending on the Q, you can usually cut out somewhere from 215 - 275 Hz as the center frequency with the Q around 1.4
There are times that for what ever reason having the center frequency around 240 just does not sound good, that's fine. All of this depends on which amp, cab, pedal, guitar combination, so don't be confined. Try out several settings of Freq, Q, and Gain - and be aware that even small adjustments in any of these can make the difference between Gold or Mold (great or not) Changing the Q from 1.7 to 1.5 could make all the difference, setting the center Freq. to 271 Hz instead of 280 could turn a Rig from a loser to a winner, or maybe the center Freq. is set at 323 Hz. So poke around, learn the amps and what settings work best for you.
Also keep in mind that once you start adding in more guitars, bass, drums, vocals, ect... you may need to roll off more of the low end on the guitars - say from around 100 - 160 and down. Having too many low-end frequencies all competing to be heard will also contribute to MUD. Another thing to keep in mind, is that what can be MUD for guitar, may be a needed frequency range for another instrument that without it, may sound weak - such as bass. If you dial out too much from say 200 - 300 Hz on your bass track, you may start to lose the ineligibility of the bass as that is part of the Bass Range and Upper Bass/Bass Presence Range.
And lastly, don't be afraid to cut some frequencies from the possible Mud range and boost others. You may find that cutting around 265Hz with a wide Q (1 - 2.1) and then boosting 200Hz with a narrow Q (6 - 7.5) will give you the sound you want.
So use the 160 to 320 Hz range as a simple guide, but always let your ears be the final judge.