Until now, TV and radio signals have been broadcast on an analogue platform. Analogue television requires a large amount of bandwidth to transmit the picture and sound information.
The more bandwidth, the more can be carried - a bit like traffic lanes on a highway. Analogue signals use a lot of bandwidth, limiting the amount of signal that can get through at any one time.
Digital signals, on the other hand, require much less bandwidth - up to 9 times as much digital information can be carried in the same bandwidth!
The result is a brighter, sharper picture and much better sound quality; like the difference between an old video cassette and a DVD.