Speech coding at 4 kb/s and lower using single-pulse and stochastic models of LPC excitation

The authors present an LPC (linear predictive coding) speech coder that classifies speech into periodic and nonperiodic intervals. The coder uses a stochastic codebook, as in CELP (code excited linear prediction), to synthesize nonperiodic speech and single-pulse excitation (SPE) to synthesize periodic speech. This coder is called SPE-CELP. The optimization of the single-pulse excitation is based on a new algorithm that determines the time instants of pitch periods within a short interval of periodic speech of approximately 32 ms. It thus causes a coding delay that is acceptable for many applications. Results using a fixed delta-impulse shape and time-varying pulse shapes obtained from codebooks are reported