A code-excited linear predictive coder or decoder for a speech signal has an adaptive codebook, a stochastic codebook, and a pulse codebook. A constant excitation signal is obtained by choosing between a stochastic excitation signal selected from the stochastic codebook and an impulsive excitation signal selected from the pulse codebook. The constant excitation signal is filtered to produce a varied excitation signal more closely resembling the original speech signal. The varied excitation signal is combined with an adaptive excitation signal selected from the adaptive codebook to produce a final excitation signal, which is filtered to generate a synthesized speech signal. The final excitation signal is also used to update the adaptive codebook.