Plug a set of headphones into a radio tuned to an FM jazz station. Hear the hiss at the bottom of the range and the fuzz at the top. Remember why you like compact discs. But don't be impatient: wait eight seconds. An "HD" light appears on the tuner. And now the bottom drops out. The hiss turns to silence. The stereo channels separate, opening a cramped room into a performance hall. And the high fuzz is now crisp high notes from a trumpet or Ella Fitzgerald. You have just heard terrestrial digital radio. Or you would have--if you could get your hands on a receiver.
Digital AM sounds like present-day stereo analog FM
If you want to offer extra choice via digital FM, it will be at the expense of sound quality.