Let the hive mind of Engadget get that for you.
"I've found myself using my PC for a lot of conversations lately, and I'm also considering recording a podcast to share with anyone who will listen. There are tons of USB headset / microphones out there, and I'm hoping someone has some solid recommendations based on experience. I'll consider both headsets and standalone mics, by the way, but I'd like to keep the bill under $100 if possible. Help!"
They do this internally, but you can check it for yourself as well. Just get a PC capture card that will capture both OTA and QAM. Then capture the same channel from each source and compare. Here in Tampa, Ch28 isn't recompressed that much, but other channels are.