Selective modeling of the LPC residual during unvoiced frames: White noise or pulse excitation

This paper presents a new method of modeling the LPC residual during unvoiced speech for voice coding at 4.8 kb/s. With this method, speech is synthesized using one of three excitation types: periodic pitch pulses, random noise, or multipulse. By using multipulse excitation it is possible to accurately produce speech which is difficult to model using noise and pitch pulses alone [1]. Since multipulse is only used where appropriate, efficient, sub-optimal methods of calculating the pulse amplitudes and positions are adequate, simplifying the implementation into 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.