Vocoder is a neologism made from the words "voice" and "coder", i.e. speech coder. It is a system for the analysis of speech signals. As far as voice signal transmission is concerned, it is done with low transmission bandwidth and low data rate.
Vocoders analyze the speech signal and generate analysis parameters from it. From these, speech is generated again at the receiving end with the aid of a synthesizer.
In terms of procedure, the vocoder analyzes the speech information to be transmitted on the basis of the fundamental frequency and the phonation. The speech information is filtered in signal filters. A signature is formed from the frequency components and their signal level. The transmitted parameters are converted so that they are reconstructed in the receiver to the original speech signal. The audio signal present at the output of the vocoder corresponds to a synthetic sound, a robotic vocal sound pulsating in rhythm with the speech input.