A Comparative Study of Speech Coding Techniques for Electro Larynx Speech Production

Abstract

Speech coding is a method of earning a tight speech signals representation for efficient storage and efficient transmission over band limited wired or wireless channels.  This is usually achieved with acceptable representation and least number of bits without depletion in the perceptual quality. A number of speech coding methods already developed and various speech coding algorithms for speech analysis and synthesis are used. This paper deals with the comparison of selected coding methods for speech signal produced by Electro Larynx (EL) device.  The latter is a device used by cancer patients with their vocal laryngeal cords being removed.  The used methods are Residual-Excited Linear Prediction (RELP), Code Excited Linear Prediction (CELP), Algebraic Code Excited Linear Predictive (ACELP), Phase Vocoders based on Wavelet Transform (PVWT), Channel Vocoders based on Wavelet Transform (CVWT), and Phase vocoder based on Dual-Tree Rational-Dilation Complex Wavelet Transform (PVDT-RADWT). The aim here is to select the best coding approach based on the quality of the reproduced speech. The signal used in the test is speech signal recorded either directly by normal persons or else produced by EL device. The performance of each method is evaluated using both objective and subjective listening tests.  The results indicate that PVWT and ACELP coders perform better than other methods having about 40 dB SNR and 3 PESQ score for EL speech and  75 dB with 3.5 PESQ score for normal speech, respectively.