I’m not surprised that you have that experience with opera on TV. The real beauty of the operatic voice only comes to light when heard live, in person. The sound requirements of broadcasts require singers to be miked (sp?) “up close and personal”, which cuts most of the overtones out of their sound.
You may very well have heard muddy singing–I can’t say–but I would encourage you to go and hear something live if you get the chance. It’s a completely different experience. I would liken the extent of the difference to that of talking to someone on the phone vs. face-to-face conversation. Not only can you hear them fully without any intervening media, but you can see them and feel their presence as well.
“I never forget a face, but in your case I’ll make an exception”
–Groucho Marx