An acoustic camera approach to studying nasality in speech: The case of Polish nasalised vowels

Abstract The purpose of this research is to introduce an acoustic camera method to analyze nasality in speech. The input information is generated using an acoustic camera device composed of a 16-channel audio recorder with a microphone array, a high-speed video camera, and Carstens articulograph (model AG500). The linearly constrained minimum variance algorithm is used to provide illustrations of the spatial acoustic field distribution. Acoustic pressure distribution is determined as related to the location of oral, nasal, and oronasal resonances, as well as the root mean square value of the pressure. Durations of particular types of resonances activated in the course of speech sound production are also specified. An example application of the method is discussed for Polish nasalized vowels. The internal structure of the vowels is heterogeneous and involves alternate or simultaneous activation of oral and nasal resonances. The order of appearance of these resonances and their percentage share in the realization of the vowels is determined based on the spatial distribution of the acoustic field. The vowels' structure is demonstrated to be even more complex than suggested in former studies. Furthermore, the proportion of nasality is found to vary significantly between the vowels