All headphones muffled

I have an iMac (21.5" late 2012) running macOS 10.15.7. I have been using a set of ligitech USB headphones for years, and it's worked great. Yesterday, after I got done with a virtual call, I stepped away and when I came back, the sound was off.

At first, I was getting no sound from my headphones at all. I unplugged them, and plugged them back in, and was able to get sound. However, now it's muffled (sounds like it's missing the midrange sounds, or that they are significantly muffled). I tried a pair of bluetooth headphones, which had never been paired to the computer before, and work fantastic with my iPhone 12, and had the same quality sound. I tried running sound through the speakers, and they are just fine, no problems.

I tried restarting the machine. I have also tried resetting the SMC by shutting down the machine, unplugging it for at least 15 seconds, plugging it back and waiting 5 seconds, then restarting the machine. Still no difference in sound.

I find it odd that it was only after this particular call that it happened. I have since deleted the app used to make the call, hoping that might help, but no difference so far.

Any other suggestions?