A study on amplitude variation of bone conducted speech compared to air conducted speech

This paper investigates the amplitude variation of bone conducted (BC) speech compared to air conducted (AC) speech. During vocalization, vibrations travel through the vocal tract wall and skull bone, which can be captured by placing a bone-conductive microphone on the talker's head. Amplitude of this recorded BC speech is influenced by the mechanical properties of bone conduction pathways. This influence has relation with the vocal tract shape that determines the resonances of the vocal tract filter. Referring the vocal tract output as AC speech for simplicity, amplitude variation of BC speech can be described with respect to the location of the formants of AC speech. In this paper, amplitude variation of BC speech of Japanese vowels and long utterances have been investigated by exploiting the locations of first two formants of AC speech. Our observation suggests that when the first formant is very low with higher second formant, the relative amplitude of BC speech is amplified. As opposed to this, relatively higher first formant and lower second formant of AC speech cause reduction of the relative BC amplitude.