Surveying the nasal peak: A1 and P0 in nasal and nasalized vowels

Abstract

Nasality can be measured in the acoustical signal using A1-P0, where A1 is the amplitude of the harmonic under F1, and P0 is the amplitude of a low-frequency nasal peak (~250 Hz) (Chen 1997). In principle, as nasality increases, P0 goes up and A1 is damped, yielding lower A1-P0. However, the details of the relationship between A1 and P0 in natural speech have not been well described. We examined 4778 vowels in French and English elicited words, measuring A1, P0, and the surrounding harmonic amplitudes, and comparing oral and nasal tokens (phonemic nasal vowels in French, and coarticulatorily nasalized vowels in English). Linear mixed-effects regressions confirmed that A1-P0 is predictive of nasality: 4.16 dB lower in English nasal contexts relative to oral and 5.73 dB lower in French (both p<0.001). In English, as expected, P0 increased 1.42 dB and A1 decreased 3.93 dB (p<0.001). In French, however, both A1 and P0 lowered with nasality (5.73 and 0.93 dB, respectively, p<0.001). Even so, in both languages, P0 became more prominent relative to adjacent harmonics in nasal vowels. These data reveal cross-linguistic differences in the acoustic realization of nasal vowels and suggest P0 prominence as a potential perceptual cue to be investigated.