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“The Vocoder for the 21st Century

The Vocoder was invented by Homer Dudley in the mid-30’s of the last century. Dudley worked at Bell Laboratories, and this is where the first Vocoder took shape.
The basic function of a Vocoder is characterized by an analysis of the input signal, usually speech but other type of inputs can also be very interesting. In a special filter bank, a spectral analysis is performed and signals are developed which follows the amount of spectral energy in each channel. Another part of the analyzer tests if there are unvoiced or voiced sounds at any particular time and extracts the pitch of the voiced sounds. The output section of the vocoder consists of a stereophonic synthesis filter bank which assembles the new synthetic speech from the characteristic filter envelopes from the analysis stage together with an external or internal replacement signal.

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