A speech coding system and associated method relies on a speech encoder (15) and a speech decoder (20). The speech decoder (20) includes an LPC synthesis filter (90), a Gaussian noise generator (80) for generating unvoiced excitation, an epoch-adaptive harmonic generator (70) for generating voiced excitation for pitch harmonics below voicing cutoff frequency, and an excitation summer (72) for summing the voiced and unvoiced excitation generated by the Gaussian noise generator (80) and the harmonic generator (70). The output of the excitation summer (72) is provided to the LPC synthesis filter (90) to generate synthesized speech. The system and method provides natural sounding synthesized speech at a low bit rate.