too many cats in the sack - 3 instruments competing

carve, with extreme prejudice.
 
find, on line, a chart, that shows the frequency range of all instruments, and where they share the center freq,
shift one to the left, one to the right...
where the freqs overlap, roll them off of one, while leaving the other to take over there...
etc, etc, ad naseum, rinse and repeat,
after 10,000 hours of doing this, you will be an expert.
 
 
in other words,
there are no shortcuts,
but to sit and learn by doing.
 
get SPAN.
 
study.
listen
 
trust your mixing environment, or change/improve it.
get better monitors.
 
the list is long.......

Check out MSpectralDynamics from MeldaProduction.  explained in great detail here:
 
http://soundbytesmag.net/spectraldynamicsdynamiceq/

Instruments being out of tune with each other stick out in that region as well, compounded by tuning being more difficult on lower frequencies. Another thing worth trying is using Melodyne to force pitch center on that passage, but the cutting/notching mentioned above would come high on my list too.

Don't forget shelf setting in EQ nodes. You can lower a range evenly. Try that on the guitar maybe.

Also, psycho-acoustically the fundamental of a note doesn't have to be present. It can be EQ'd out and the brain fills it in by using the notes' harmonics. I would think you could HPF the guitar and just let the bass/drums provide all that low frequency content. The guitar will still be "heard" playing those low notes.

Guitarhacker
Words to live and mix by:
 
Nothing is sacred.
 
Less is More.
 
 
Short explanation:  Everything in a song can be cut, edited, removed, changed... not much is carved in stone and use only what you really, really, need to use to accomplish the goal.  Then re-assess and reapply the rules previously stated.

Yeah, Jimmy Page did not NEED all those guitar tracks.

Lord Tim has the right idea and it is all about the arrangement first and foremost and I mean what are the parts actually saying. I bet too may parts are overlapping each other instead of weaving in and out of each other.
 
EQ and compression and stuff are all poor relations to actually sorting out the arrangement. What a great producer does is cut the music around a lot. I bet I could cut the parts up in such a way that the same phrases and intentions are applied but instead hardly anything is overlapping or playing at the same time.
 
You can be too precious about what you have played. If you handed this section over to a top producer the first thing they would be doing is removing unwanted overlapping stuff. You need to create the air and see what I have called the black backdrop behind the music. If you cannot see the black backdrop or it becomes a grey wash type of backdrop you have simply got too much going on.
 
When you get this stuff right you can actually have solid EQ and much more fuller sounding parts that have much more weight and body to them. Hacking out stuff EQ wise to make things audible is a poor way to do it. You end up with thin sounding parts.

bitflipper
Sometimes the mixing desk becomes a battlefield triage tent. Who's most likely to punch you in the face, the drummer or the bass player? You can only save one of them, the other has to die.
 

 
Yikes!  Ed...we better lie LOW for a while.
 
(See what I did there!)
 
 
 
Arrangement is key.  Less clutter.  

Sometimes if I have these clashes, I like to into a part (guitar riff, perhaps) in isolation. At the beginning of a song, bring it in, by itself, or nearly so. Keep it prominent for 8 or so bars - the listener will get used to it being there, nice and up front.
 
Then when you add the next element, you can drop the guitar 1 db or so, the listener will know it's there because they are used to its being there. You can raise volume on the next element.
 
When you bring in #3, lower number two. etc. etc.
 
This in addition to panning/eq can help unmash the parts. And as they say, for most people it's all about the vocal anyway.
 
cheers,
-Tom

Another real world example is my main band LORD. If you ever listen to us (link in the signature below), the first thing you'll hear is a LOT of layers, like literally hundreds of vocal layers, up to 25 guitar tracks, synths, loops, sometimes 2 different bass tracks, and usually very fast and busy parts, especially drumming wise where the kicks can be very full on.
 
Mixing that is a HUGE challenge, let me tell you! But where possible, yes - the arrangement favours the most prominent element. Is the guitar riff the key? If so, does it REALLY need the kick drums to follow every note? Can the bass do something in a different octave? Hang on a note? Stop entirely?
 
And yes, sometimes it's absolutely necessary to be that busy. You'll have a very proggy tech riff where everything is playing - the guitars and bass are mirrored over the top of a double kick section, with orchestration and vocal adlibs - and that's crucial to getting the intent of that part across. It's in those places that you really need to put your objective engineer hat on and decide what needs to take focus most of all, and put any ego aside (and as the lead vocalist and guitarist that also does the keyboards, that's a hard ask for me! HAHA!)
 
But yeah, some great suggestions in this thread and things I've pulled out pretty often when I manage to write myself into a tangled mess! 
 
One last thing to consider is your ears lie.
 
I think I mentioned in anther thread somewhere that I made a complete disaster area of our first proper album back in the 90s. I listened to each track in isolation, and got everything sounding absolutely MASSIVE for each track on its own, and then naively sat there like a drooling idiot wondering why it all sounded like a muddy mess once everything was all combined in the mix, and then every change I made after that was just more tangling. I'd turn up the guitars and you'd lose the kicks. I'd turn up the kicks and then the bass was getting lost. I'd turn up the bass and then the guitars sounded wimpy. So I'd turn up the guitars and... repeat from step one, watching the other band members getting more and more angry I'm wasting our recording budget.
 
That's just half of it. The other half is your ears really get attuned to what you're listening to, and it's a very distorted view of reality. This same album is a good example. We finally got something we all could live with (barely) and took it to get mastered. We put it next to the reference tracks and everything else we listened to sounded wrong and kind of thin and midrangey. In actual fact, everything else was fine (of course it was, since it was all done by pros with a huge budget), and it was our stuff with no mids and a sloppy low end. But none of us could hear it objectively anymore.
 
You really need constant reality checks with commercial mixes as you go to keep your brain in check. Changing anything, even for the better, will sound wrong if you're caught up in your own mix. So cutting the lows on the guitars to carve space will make them sound bad if you're used to that mud being there, but if you compared it to a commercial mix, you'd probably find that's exactly what they did to get that to sound so good.
 
Anyway, just a couple more things to consider. 

I remember reading an interview with Ken Scott. He said the most universally ugly frequency is 200hz.  So he basically does a cut @ 200 on almost everything. I didn't know if it was some sort of joke so I tried it and damn if it doesn't make a great place to start.

yes, i'd agree with jeff on using the scoop....
on a parametric, i'd start with a real High Q, and a real deep BOOST to find the exact center point of the mud...
 
then, go the opposite way, but go to a shallow Q (like 4) and only do about 1-2db of cut.....
to taste.....
 
i tend to eq individual tracks, to get rid of mud and maximize the low end,
sometimes it's confusing solo'ing a track to do that,
but after some time, you kinda KNOW you are hearing mud on tracks you know don't need that freeq......