SELECTIVE MODELING OF THE LPC RESIDUAL DURING UNVOICED FRAMES: WHITE NOISE OR PULSE EXCITATION.

Abstract

The authors present a method of modeling the LPC residual during unvoiced speech for voice coding at 4. 8 k/s. Speech is synthesized using one of three excitation types: periodic pitch pulses, random noise, or multipulse. By using multipulse excitation, it is possible accurately to produce speech which is difficult to model using noise and pitch pulses alone. Since multipulse is only used where appropriate, efficient suboptimal methods of calculating the pulse amplitudes and positions are adequate, simplifying the implementation as a real-time system. The synthetic speech may be coded at 4. 8 kb/s since multipulse, used only where appropriate, suffers little quality loss when quantized. A method of determining which excitation type is to be used is discussed. Formal listening test results are also presented.