Speech Compression of Thai Dialects with Low-Bit-Rate Speech Coders

Problem statement: In modern speech communication at low bit rate, speech coding deteriorates the characteristics of the coded speech significantly. Considering the dialects in Thai, the coding quality of four main dialects spoken by Thai people residing in four core region including central, north, northeast and south regions has not been studied. Approach: This study presents a comparative study of the coding quality of four main Thai dialects by using different low-bit-rate speech coders including the Conjugate Structure Algebraic Code Excited Linear Predictive (CSACELP) coder and the Multi-Pulse based Code Excited Linear Predictive (MP-CELP) coder. The objective and subjective tests have been conducted to evaluate the coding quality of four main dialects. Results: From the experimental results, both tests show that the coding quality of North dialect is highest, meanwhile the coding quality of Northeast dialect is lowest. Moreover, the coding quality of male speech is mostly higher than that of female speech. Conclusion: From the study, it can be obviously seen that the coding quality of all Thai dialects are different.