On the potential for artificial bandwidth extension of bone and tissue conducted speech: a mutual information study

To enhance the communication experience of workers equipped with hearing protection devices and radio communication in noisy environments, alternative methods of speech capture have been utilized. One such approach uses speech captured by a microphone in an occluded ear canal. Although high in signal-to-noise ratio, bone and tissue conducted speech has a limited bandwidth with a high frequency roll-off at 2 kHz. In this paper, the potential of using various bandwidth extension techniques is investigated by studying the mutual information between the signals of three uniquely placed microphones: inside an occluded ear, outside the ear and in front of the mouth. Using a Gaussian mixture model approach, the mutual information of the low and high-band frequency ranges of the three microphone signals at varied levels of signal-tonoise ratio is measured. Results show that a speech signal with extended bandwidth and high signal-to-noise ratio may be achieved using the available microphone signals.