vocoder(redirected from Channel vocoder)
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a system of telephone communication in which the transmitted signals are not those of speech but rather of a special representation of speech in an encoded form. In this system a sound analyzer at the transmitting end forms coded signals from the speech signals; at the receiving end a synthesizer artificially restores the speech signals from the coded signals. With a vocoder it is possible to achieve a coefficient of syllabic articulation of 83 to 85 percent (this coefficient is between 90 and 91 percent for the ordinary telephone communication). The coding reduces the width of the frequency passband required for the communication channel to 250-350 hertz, as compared with the band from 250 to 3,500 hertz of the ordinary telephone communication, thus increasing the carrying capacity of a long-distance communication line by ten to 13 times.
For example Qualcomm uses a vocoding algorithm to compresses voice data in digital communication systems such as wireless CDMA and Eudora voice attach.