Analogue radio is an old technology. It is being superceded now, especially on FM, by Digital Audio Broadcasting (DAB), which needs DAB radio receivers to turn the signal into sound.
DAB can pack more stations into the same frequency spectrum and at the same time give higher quality, interference free reception. Analogue signals are particularly subject to interference which cannot easily be eliminated. This may take the form of random noise or arise from reflections from hills and buildings. Digital signals can be easily processed to removed random noise while reflections from hills and buildings – multipath signals – can actually be used to improve the quality of the signal received by clever signal processing.
DAB transmitters all use the same carrier frequency, with digital signals split into groups so they can be transmitted alongside each other using a system called multiplexing – the same system is used to send telephone calls over the same cable. The DAB receiver decodes the signal it receives into the signal from each station.