Issues in high quality LPC analysis and synthesis

This paper deals with careful non-real-time LPC analysis. A baseline system is first described. lt uses a pitch-synchronous covariancemethod analysis with a laryngograph signal providing the pitch synchrony. Work to improve the voicing decision and F0 determination and to find a better voiced excitation waveform is described. Setting a lower Iimit on the value of B 1 is found to be useful. Buzziness in the synthesis of voiced fricatives can be reduced by adding white noise to the excitation, and regions where this should be done can be automatically detected using three parameters: total power, the ratio of high-frequency power to total power, and 8 1. The location of the analysis frame for covariance-method analysis is found to be unimportant. A modified autocorrelation method with a carefully placed, Hanning-windowed, pitch-synchronous analysis frame is found to give results that are as good as or iletter than the covariance method. Finally, a method of resynthesizing speech using a modified LPC residual is described. The method allows prosody and formant parameters to be manipulated with minimal degradation.