Ericsson Radio Systems AB, S-164 80 Stockholm SWEDEN * Erisoft AB, S-951 10 Lule% ABSTRACTThe bit rate of CELP coders can be significantly reduced by increasing the length of the analysis frame and the subframes. When frame lengths of 30-40 ms and above are used, new problems that reduce speech quality do become prominent. The paper discusses the origin of some of these problems, and suggests techniques that can be applied in order to improve quality and reduce computational complexity for long frames and subframes. Promising results have been obtained for a new interpolation constrained time variable LPC algorithm and, in particular, for a new double mode LTP structure. Experimental results on delayed decision tree coding and low complexity innovation coding are also presented.
11-6040-7803-0946-4/93 $3.00 0 1993 IEEE
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