Pre-Processing for Performance Enhancement of Speech Recognition in Digital Communication Systems

Speech recognition in digital communication systems has very low performance due to the spectral distortion caused by speech codecs. In this paper, the spectral distortion by speech codecs is analyzed and a pre-processing method which compensates for the spectral distortion is proposed for performance enhancement of speech recognition. Three standard speech codecs, IS-127 EVRC, ITU G.729 CS-ACELP and IS-96 QCELP, are considered for algorithm development and evaluation, and a single method which can be applied commonly to all codecs is developed. The performance of the proposed method is evaluated for three codecs, and by using the speech features extracted from the compensated spectrum, the recognition rate is improved by the maximum of 15.6% compared with that using the degraded speech features.