IMPROVEMENT OF LOW BIT RATE LPC VOCODER

Linear predictive technique has been widely used for speech signal processing,especially forlow bit rate vocoder in recent years.However the conventional fixed frame processing does not suit wellwith speech signal for its nonstationary behavior.Also it is unreliable to extract pitch from theparameters(e.g.residual)obtained by that method.Due to these reasons,speech quality may be ad-versely affected.In order to increase the quality and intelligibility,this papers presents improvementsto the following three aspects:(1)Using adaptive ladder form algorithm instead of conventional LPCto obtain more accurate estimation of the vocal-tract transfer function.(2)Adapting nonuniformsampling of speech parameters with constrained interval to improve performance of synthesizedspeech during fast transienis.(3)Improving Gold-Rabiner pitch extraction technique for simplicity andreliability.The computer-simulated results show that the 2.4 kb/s vocoder gives the synthesized speechwith good intelligibility and quality,and