Mediumband speech processor with baseband residual spectrum encoding

The Navy has developed a Multirate Processor (MRP) which generates digitized speech at 2.4, 9.6, and 16 kb/s by the linear predictive coding principle. This multirate capability is achieved by embedding the 2.4 kb/s data in the 9.6 kb/s data stream and the 9.6 kb/s data in the 16 kb/s data stream. Conversion between the rates is accomplished by truncating a certain portion of the bits from the higher-data rate signal or appending extra bits to the lower-data rate signal. The MRP mediumband (9.6 kb/s or 16 kb/s) mode is a baseband residual excited LPC in which the baseband residual is transmitted in terms of Fourier spectral components. Under various operational conditions, the Diagnostic Rhyme Test (DRT) scores for the 9.6 kb/s rate of the MRP compare favorably to the DRT scores of an existing 16 kb/s rate Continuously Variable Slope Delta (CVSD) encoder.