When I make or receive a voice call on a cellphone, what happens to the audio? Is my voice transmitted as a continuous analog signal, or is it sampled and sent as digital data? I'm also curious whether the answer differs for older cellular systems or traditional landlines.
4 Answers
Traditional copper landlines can still carry an analog signal from the handset to the first local switch. After that, the call is generally converted to digital for transport through the telephone network. Many newer home and business phone services are digital from the start, often using fiber or internet-based systems.
The earliest cellular systems, such as AMPS, used analog FM voice transmission. Modern cellular networks have been digital for many years, so an ordinary current cellphone call is digitally encoded and transmitted.
There’s a useful distinction here: sound in the air is an analog, continuously varying pressure wave, but the phone’s representation of that sound is digital after the microphone signal is sampled. The receiving phone converts it back to analog for its speaker.
Modern cellphone calls are digital. The microphone converts your voice into digital samples, which are compressed and transmitted as data over the cellular network. At the other end, the data is converted back into an analog electrical signal to drive the speaker, producing the sound you hear.
So a landline handset may still use analog audio locally, even though most of the rest of the call is handled digitally?