Vowel formant discrimination in quiet, speech-shaped noise, and babble for natural speech

Abstract

Vowel formant discrimination in quiet and in noise for naturally spoken vowels was investigated. The stimuli were seven isolated vowels /i, u, I, ε, ʌ, æ, a/ recorded from a female talker and resynthesized using STRAIGHT with and without formant shifts. Vowels were presented in two noise types, long-term speech-shaped noise (LTSSN) and twelve-talker babble. ΔF was measured for F1 and F2 in quiet and noise with five signal to noise ratios (SNRs), +4, +2, 0, −2, and −4 dB. Adaptive tracking procedures were used, interleaving quiet and SNR levels for one formant at a time. Overall, results suggested that formant frequency, SNR, and noise type had significant effects on ΔF. For either LTSSN or babble, ΔF as a function of formant frequency showed four significantly different patterns, depending on the SNRs. ΔF as a function of SNR also showed several different patterns for different formants. A surprising result was that ΔFs were higher at −2 dB than those at −4 dB in babble, particularly in the F2 region. In addition, performance in babble was significantly better than that in LTSSN at comparable SNRs. These results will be examined by partial loudness models. [Work supported by NIHDCD-02229.]