Telephony is voice communication between remote parties over telecommunications networks. Long-distance speech or telephony is carried out using telephones that convert speech into electrical signals, which are then transmitted via the telephone network.
Because of the high redundancy of human speech, the lowest possible frequency band is used for reasons of frequency economy. The decisive factors for the bandwidth of the frequency band were the speech recognizability of the subscribers and sufficient sentence and syllable intelligibility. This is 3.1 kHz, in the frequency range from 300 Hz to 3.4 kHz.
Using speech memories, speech communication can also be time-delayed.