Normalizing nasality? Across-speaker variation in acoustical nasality measures

Abstract

Although vowel nasality has traditionally been investigated using articulatory methods, acoustical methods have been increasingly used in the linguistic literature. However, while these acoustical measures have been shown to be correlated with nasality, their variability across-speakers is less-well investigated. To this end, we examined cross-speaker variation in coarticulatory vowel nasality in a large collection of multi-speaker English data, comparing measurements in CVC and NVN words at two points per vowel. Two known correlates were analyzed: A1-P0, where A1 is the amplitude of the harmonic under F1, and P0 is the amplitude of a low-frequency nasal peak (Chen 1997), and the bandwidth of F1 (Hawkins and Stevens 1985). Speakers varied both in terms of baseline measurements (e.g., the mean measurements in oral versus nasal vowels), and in the oral-nasal range (the measured difference between oral and nasal). This suggests that although analyzing centered within-speaker differences is unproblematic, the comparison of raw nasality measurements across speakers is unlikely to yield meaningful data. Moreover, this suggests that the perception of vowel nasality may require some process of speaker normalization, much like other aspects of vowel perception. Some suggestions for normalizing nasality measurements in research will be offered.