When the velum lowers during vowels, the velopharyngeal port is opened, and there is acoustic coupling between the nasal cavity and the main vocal tract, giving rise to a distinct acoustic quality which we call nasality. Nasal coupling results in energy losses at low frequencies, damping of oral formants (especially F1), and introduction of nasal formants corresponding to the resonances of the nasal cavity and sinuses. These spectral modifications are gradient, increasing with degree of velar lowering; this relationship suggests that velar position may be recovered from the acoustic signal by measuring the degree of nasality in the vowel. However, the acoustic effects of nasalization vary not only with velar position, but also across different speakers and vowels, making it difficult to identify an acoustic dimension corresponding to nasalization.
Based on my MA thesis I present a methodology for acoustic measurement of nasality in vowels which attempts to overcome this contextual variability by normalizing the measurement over different speakers and vowel contexts. The measuring technique is trained on a phonetically balanced corpus for each speaker to generate a speaker-specific model. The system is trained and tested on recordings of 17 native speakers of three languages.