This is a decent dummy introduction to what DAB is:

https://en.wikipedia.org/wiki/Digital_audio_broadcasting

> DAB is more efficient in its use of spectrum than analogue FM radio, and thus may offer more radio services for the same given bandwidth. DAB is more robust with regard to noise and multipath fading for mobile listening,[3] since DAB reception quality first degrades rapidly when the signal strength falls below a critical threshold, whereas FM reception quality degrades slowly with the decreasing signal.