Digital signals maintain their quality better than analogue signals.
All signals become weaker as they travel long distances. They may also pick up random extra signals. This is called noise. It is heard as crackles and hiss on radio programmes. Noise affects both analogue and digital signals.
Noise adds extra random information to analogue signals. Each time the signal is amplified, the noise is also amplified. Gradually, the signal becomes less and less like the original signal. Eventually, it may be impossible to make out the music in a radio broadcast against the background noise, for example.
Noise also adds extra random information to digital signals. However, this noise is usually lower in amplitude than the amplitude of the ON states. As a result, the electronics in the amplifiers can ignore the noise and it does not get passed along. This means that the quality of the signal is maintained, which is one reason why television broadcasters have changed from analogue to digital and radio broadcasters are in the process of changing.
Because digital signals can carry more information per second than analogue signals, higher quality programmes or more channels can be broadcast. Another advantage of digital signals is that information can be stored and processed by computers.
This slideshow demonstrates how the amount of noise affects analogue and digital signals: