Microphone (mic) presence refers to the live human host that is the hallmark of quality radio. Broadcast programming typically includes an on-air personality, known as an announcer, presenter, or disc jockey (DJ), who introduces news segments or musical numbers, provides interstitial banter, and (often) interacts with listeners in real time, either by telephone or e mail. This imparts a quality to the listening experience known as "mic presence". Without it, you don't have real radio.To date, true mic presence is rare in net-only stations; Radio Caroline is an example of one that offers a growing number of live blocks in its daily schedule. (Readers who know of others are encouraged to leave the names and URLs of the stations in question in a comment below.) Aside from that, live DJs are mostly heard online via broadcast stations that provide a parallel livestreaming service. It's the sincere hope of NRB that as funding norms develop here, live mic presence will become common among new-frontier stations as well.
(Photo of Mister X, aka Derek, of KZYX [Mendocino, California], courtesy of Wikimedia Commons and a generous photographer.)