Effect of speech coders on speech recognition performance

Speech coders with bitrates as low as 2.4 kbits/s are now being developed for speech transmission in the telecommunications industry. For speech coders to work at this reduced bitrate, some speech information has to be removed and it is only natural to expect that the performance of speech recognition systems will deteriorate when coded speech is applied as input to a recognition system. The results of a study to examine the effects speech coders have on speech recognition am presented. Six different speech coders ranging from 4.8 kbits/s to 40 kbits/s are used with two different speech recognition systems: (1) isolated word recognition and (2) phoneme recognition from continuous speech. The effects on speech recognition performance by tandeming each of the speech coders are also presented.