On Equalization of Bone Conducted Speech for Improved Speech Quality

We propose an equalizer that attempts to improve the perceived speech quality of bone-conducted speech input with ear-insert microphones, which can provide clean speech input in noisy environments. We first show that the transfer characteristics of bone-conducted speech are both speaker and microphone dependent, and propose an equalizer which is trained using simultaneously recorded airborne and bone-conducted speech. The short-term FFT amplitude ratio of airborne and bone-conducted speech is used. The amplitudes are averaged and smoothed extensively before the ratio is calculated. The trained equalizer is applied to bone-conducted speech in the frequency domain. We show that the proposed equalizer provides notable quality improvement on the bone-conducted speech input, both subjectively and objectively. We also show that the application of spectrum subtraction also helps decrease some constant level background noise found in these types of microphones