What are the differences between analogue and digital broadcasting?

An analogue (or analog) broadcast signal directly represents the transmitted sound and picture through deliberate variations in signal voltage and radio frequencies. All systems preceding digital television were analog television systems. For a more detailed description see: http://en.wikipedia.org/wiki/Analog_television

Digital broadcasting works by translating sound and picture into digital data rather than analogue waveforms. There is a worldwide transition to digital broadcasting but a much slower process of digitalisation for radio.

Digital links, thanks to the use of data compression, generally have more efficient bandwidth usage than analog links, which allows a content provider more room to provide services, or to provide a higher-quality signal than had been previously available.

For a more detailed description, see:

http://en.wikipedia.org/wiki/Digital_broadcasting