Digital transmission of speech presents the opportunity to provide a more secure and bandwidth efficient service with a consistent quality. The feasibility and cost efficiency of future systems depends largely on the availability of low bit rate vocoders. Orthogonal transformations offer a means for reduction of the bit rate necessary for the transmission of speech signals. The ability to reduce the bit rate resides in the fact that the variance of the orthogonal function coefficients is far less than the variance of the speech itself. Discrete Walsh and Haar transforms are examined for their capacity to reduce the bit rate necessary to transmit speech signals. The performance of these transforms when applied to bit rate reduction has been measured in a mean square error sense (signal-to-noise ratio). High quality speech reproduction is obtained at bit rate of 24 Kbps.
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