Selective pole modification-based technique for the analysis and detection of hypernasality

Inadequate velopharyngeal closure, due to structural or neurological problems, allows air to pass through the nasal cavity leading to introduction of inappropriate nasal resonances during speech production resulting in hypernasal speech. Our previous work on the acoustic analysis of hypernasal speech using group delay function for the detection of hypernasality showed stable effects of vowel nasalization in the low frequency region. In the current work linear prediction (LP)-based pole modification technique is used as a detection method for hypernasality. Lower order LP analysis frequently fails to resolve two closely spaced formants. On the contrary, increasing the LP-order may show spurious peaks in the low frequency region for the normal speech also, that is due to pitch harmonics. To disambiguate this in the present study using a higher order LP spectrum, the pole corresponding to strongest-peak in the low frequency region is defocussed and a new signal is resynthesized. Maximum of the cross-correlation value between the input and the resynthesized speech signal is taken as a measure for the detection of hypernasality. Speech data from 25 hypernasal speakers with unrepaired cleft-lip and palate and 25 normal speakers are considered for the analysis. The performance on hypernasality/nasal decision task is 100%.