In distinguishing between voiced and unvoiced speech elements use is made of the fact that the spectra of voiced sounds lie predominantly at or below about 1 kHz, and the spectra of unvoiced sounds lie predominantly at or above about 2 kHz. A change from a voiced sound to an unvoiced sound or vice versa always produces a clear shift of the spectrum, and that without such a change, there is no such clear shift. From the lower- and higher-frequency energy components, a measure of the location of the spectral centroid is derived which is used for a first decision. Based on the difference between two successive measures, a second decision is made by which the first can be corrected.
