A study of low bit-rate linear prediction based speech coders for Indian dialects

Speech coders based on the linear prediction model are widely in use today. This paper describes the algorithms of low bit-rate vocoders, viz. Code-Excited Linear Prediction (CELP) and Mixed Excitation Linear Prediction (MELP) and their performance for Indian dialects. A Linux platform has been used for execution of the vocoders. Mean Opinion Score testing has been performed with speech samples of Indian dialects and Indian-accented English. Waveform analysis has been done using Praat software. Results show that CELP which operates at a higher bit rate of 4.8 kb/s gives better quality output. MELP speech output is intelligible and suited for very low bit-rate (2.4 kb/s) applications. The results also highlight the need for better codebook tuning in Indian dialects.