Fretted notes above 12 on E and A string sound dull
 

Already changed strings. Tuner still recognizes the notes, they just don't ring out or have the same clarity as the others. Think it's a bass problem, or do I just need a proper set up?

that is hardly an optimal area for any bass. of course you should try to set it up properly, and also make sure the strings aren't twisted (detune the strings till they flop around and rest naturally, then tune back up making sure they don't twist). apart from that i'm not sure...you could try lighter gauge strings?

Also, could anyone upload a sample of how their bass sounds in that area if they have one on hand?

The higher up on the neck you fret, the closer the pups will be to the middle of the active length of the string, and there's more fundamental and less harmonics there. The same reason the bridge pup sounds brighter than the neck pup.

The thinner the string, the clearer the tone.

The longer the string, the longer the sustain.

It's physics... the low strings don't sound so good as you go up the neck. Go into a music store and ask to play one of the fancy basses behind the counter... I bet you find a similar problem. As IronLung1986 said, it's not an optimal area for good tone.

I tend not to see many bass songs with more than a handful of notes in that area...don't think it's a coincidence.

I think you're on to something. :)

that's pretty normal, but you can use that to your advantage. I don't play a lot above the 12th on the E string. but playing a D at the 10th fret of the E vs 5th fret of the A can give the note a little more body and a little less zing. sometimes that extra thump is just what the song needs.