Effect of Low Bit Rate Speech Coding on Epoch Extraction

Speech coding is one of the major degradation involved in building the speech systems in mobile environment. In this paper, we are exploring the effect of low bit rate speech coding on the accuracy of detection of epochs. Epoch is referred as the instant of significant excitation of the vocal-tract system during production of speech. Many speech applications depend on the the accurate estimation of the epoch locations. Epoch extraction from speech signal is challenging due to time-varying characteristics of the excitation source and vocal-tract system. For determining the epochs, two recently developed accurate methods (i) zero frequency filter (ZFF) (ii) Dynamic programming projected phase slope (DYPSA) are used. Most of the epoch extraction methods except ZFF method, attempt to remove the characteristics of the vocal-tract system, in order to emphasize the excitation characteristics in the residual. ZFF method extracts the epoch locations directly from the speech signals using impulse like nature of excitation. Speech coders used in this study are GSM full rate (ETSI 06.10), CELP (FS-1016), and MELP (TI 2.4 kbps). Performance of epoch extraction methods is evaluated using CMU-Arctic data using the epoch locations from electro-glottograph as reference.