Its primary use in this fashion is for secure radio communication, where voice has to be encrypted and then transmitted. Transmitting the parameters of a speech model instead of a digitized representation of the speech waveform saves bandwidth in the communication channel the parameters of the model change relatively slowly, compared to the changes in the speech waveform that they describe. The vocoder was originally developed as a speech coder for telecommunications applications in the 1930s, the idea being to code speech for transmission. By encoding the control signals, voice transmission can be secured against interception. This allows more speech channels to share a radio circuit or submarine cable. Since the control signals change only slowly compared to the original speech waveform, the bandwidth required to transmit speech can be reduced. The decoder applies these control signals to corresponding filters in the synthesizer. In the encoder, the input is passed through a multiband filter, each band is passed through an envelope follower, and the control signals from the envelope followers are communicated to the decoder.
Freebase (0.00 / 0 votes) Rate this definition:Ī vocoder is an analysis/synthesis system, used to reproduce human speech.
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