LiveATC is crowd sourced. You take a radio, put it on your desk and stream that to their site. To get decent audio, you need a big antenna on the roof of your house or be in the air, like aircrafts.
I'm a pilot and even on very old planes like piper cub where the radio is just a desk radio added in the cockpit, the audio is much clearer. And with something like Bose A1 (noise canceling headset, A20 and A30 now), you hear it very well.
Most the time you hear ATC perfectly as they have very large antenna. ATC will hear you worse because of the noise around you, but with good mic it is still quite OK. They have large receiver too so you can be far. The worst audio is always plane to plane, there are some situations where your are far from a plane and only hear the ATC side of the conversation. But even if those situations, you can ask ATC to relay a message. It is very rare as you hardly have any reason to talk with a plane that is 100km away on the other side of a mountain.