A vocoder (/ˈvoʊkoʊdər/, short for voice encoder) is a category of voice codec that analyzes and synthesizes the human voice signal for audio data compression, multiplexing, voice encryption, voice transformation, etc.

The earliest type of vocoder, the channel vocoder, was originally developed as a speech coder for telecommunications applications in the 1930s, the idea being to code speech in order to reduce bandwidth (i.e. audio data compression) for multiplexing transmission. In the channel vocoder algorithm, among the two components of an analytic signal, considering only the amplitude component and simply ignoring the phase component tends to result in an unclear voice; on methods for rectifying this, see phase vocoder.