Perceptually motivated spectral comparisons for automatic speech recognition
James L. Hieronymus, Roy W. Gengel · The Journal of the Acoustical Society of America · 1984
Early experiments on amplitude discrimination by Flanagan [J. Acoust. Soc. Am. 27, 1223–1225 (1955); J. Speech Hear. Disord. 22, 205–212 (1957)] suggest that second formant amplitude in synthetic vowels may vary ± 4 dB without a noticeable difference. Klatt (ICASSP 82, 1278–1281) conducted experiments changing the spectral tilt of vowels. This changed the “quality” but not the identity of the vowel. These results contrast sharply with spectral comparisons used in automatic speech recognizers—which are often based on Enclidean or Itakura distances. We used a dynamic time warp based speech recognizer to study several perceptually based spectral comparison measures. One of these measures matches the lowest frequency spectral peak in the template within ± 1.5 dB. For each subsequent peak within the template spectrum, each peak in the unknown spectrum which is within a perceptual frequency band is scored as good match if it is within ± 4 dB of the template peak. Another measure tilts the spectrum so that F1 and F2 are approximately equal amplitude and then uses a Enclidean distance measure. The results of these experiments will be reported.