The term vocoder is a contraction of voice-coder as defined by Dudley . Since the inception of the vocoder great effort and time have been expended on improving the synthesis quality of devices that code speech for efficient transmission. An excellent summary of that effort up to 1966 is presented by Schroeder . One of the major problems was the difficulty in obtaining accurate separation of the driving function behavior (fundamental frequency) from the vocal tract behavior (formant structure). The first published reference to linear prediction of speech (using maximum likelihood formulation) was in the same year [Saito and Itakura, 1966]. Linear prediction techniques have made a major impact on the development of vocoder systems, since source-tract interaction problems are efficiently resolved, resulting in improved synthetic speech quality, and since the technology is available for the necessary implementation in real-time hardware.
KeywordsCovariance Assure Autocorrelation Sine Stein
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