IMPROVE THE PERFORMANCE OF VOICE-EXCITED LPC VOCODER IN SPEECH CODING APPLICATION

Abstract

One of the fundamental problems in the area of digital speech processing is a speech coding thathas been studied for years. Speech coding simply transforms the speech signals as fewer numbersof binary digits as possible, which can be then transmitted through channels or stored in memorydevices. Due to the fact that the bandwidth of the channels is not unlimited, speech compression isneeded to let more space bandwidth; thereby more speech coded signals can be sent over samechannel bandwidth. Linear Predictive Coding (LPC) that is based on linear prediction (LP) model,which is a method to represent and analyze human speech, is one of the most common speechcoding techniques. It is used in compression the digital speech signals, resulting low bit rate. Thismethod has become the dominant technique for determine the fundamental speech parameters suchas pitch, formants, spectra, vocal tract area functions. However, the weakness of LPC is inestimating the fundamental speech parameters causes poor voice quality and performance. The aimof this paper is to build a system with precise detection of speech parameters for encoding a betterspeech quality at low bit rate. This can be done through proposing a modified version to the voiceexcitedLPC vocoder based on Discrete Cosine Transform (DCT) and quantization of residual errorwhile retaining low bit rate; hence conserve the bandwidth. Segmental power signal to noise ratio(SEGPSNR) and mean square error (MSE) as an objective measure for speech signal quality areimplemented for the proposed improvement through computer simulation using Matlab 11.