Microphones.
A microphone essentially captures audio from the original source (vocalist or instrument), converts it into an electrical signal, and transmits it down a cable. Or in the case of a wireless microphone, transmits it in a radio signal form that is captured by a receiver and then sent down the cable. The more accurately a microphone can convert a sound wave into an electrical signal, the more natural it will sound. Just like "oils ain't oils", microphones are not all the same.