A Novel Feature for Nasalised Vowels and Characteristic Analysis of Nasal Filter

Nasal tract is an important part of our vocal tract system. It provides major impact for production of nasalised and hypernasal speech. Despite it's huge importance, the effect of nasal tract is not yet largely studied. This work is done with a motivation that, understanding characteristics of nasalised vowels and nasal filter will help in detecting nasalised speech. We have designed a device to separate nasal murmur from oral speech, when nasalised speech is spoken. In this work we have analysed speech data collected from different speakers. Firstly we have analysed nasalised vowels and found a novel feature for nasalised vowels. Then, various signal processing techniques are used to analyse the variability of nasal filter for different nasalised vowels. It is found that the nasal filter, which is the reason for nasalisation of vowels, is invariant across different nasalised vowels. Nasalised speech are produced when the nasal tract gets coupled with vocal tract. When the effect of coupling is experimented from a signal processing point of view, we found that it has an effect of addition.