User-Specific Quality Problems

[doctorawesome]

I'm having a very persistent and unusual problem where specific users on my Mumble server have very poor sound quality, with robotting/choppiness and garbling, but only for me--everyone else can hear these people just fine. I have made sure that everyone on the server has the most up-to-date version of Mumble, and I have tweaked every setting I could find, particularly the jitter buffer and output delay (though I feel like I have a poor understanding of what these options do.) At a more tech-savvy friend's suggestion, I have enabled forced TCP mode, and that has diminished the problem somewhat, but the problem persists nonetheless. There's even a small degree of choppiness when people speak at the same time, but this is hard to reproduce and may not even be related. I've scoured the forums and have had a hard time finding anyone describing the problems I'm having, so I'm more or less lost. Can anybody give some advice?