A 2400 bps mixed excitation LPC vocoder

The authors present a 2400-b/s speech coder based on a novel linear predicting coding (LPC) vocoder model. This model preserves the low bit rate capabilities of the traditional LPC vocoder, but it features a more flexible parameterization of the LPC excitation signal. This allows the synthesizer to generate more realistic output speech, and it also increases the robustness of the coder to acoustic background noise. The vocoder has been implemented in a real-time system. Formal subjective testing of the coder confirms that it produces natural-sounding speech even in a difficult noise environment. In fact, diagnostic acceptability measure (DAM) test scores show that its performance is close to that of the 4800-b/s Department of Defense CELP (code excited linear prediction) coder