Influence of recording equipment on the identification of second language phoneme contrasts

This paper investigates the perceptual quality of English words recorded by different types of microphones to assess their availability in Computer Assisted Language Learning (CALL) systems. English words minimally contrasting in /r/ and /l/, /b/ and /v/, or /s/ and /th/ were recorded from native female and male speakers of American English using six different microphones. The phonemic contrasts in these recordings were then evaluated by 14 native listeners of American English. The results showed that the identification of the /r/–/l/ contrast was unaltered by the difference in microphones, whereas that of the /s/–/th/ contrast significantly dropped with several headset microphones, and that of the /b/–/v/ contrast dropped with a tie-pin microphone. These findings suggest that some microphones are not appropriate for speech perception training. Finally, a post hoc equalization procedure was applied to compensate for the acoustic characteristics of the microphones tested, and this procedure was confirmed to be effective in recovering phonemic contrasts under several conditions.