Wavelet packet entropy for millimeter wave conducted speech enhancement

A new nonacoustic sensor-based speech detecting method has been developed in our laboratory by using millimeter wave radar technology. Because of the special attributes of the millimeter wave, this method may considerably extend the capabilities of traditional speech detecting methods. However, radar speech is substantially degraded by additive combined noises that include radar harmonic noise, electrocircuit noise, and ambient noise. Therefore, this study proposes an improved spectrum subtraction algorithm that uses wavelet packet entropy analysis to detect voiced and unvoiced sections in an adaptive manner. Use of this algorithm leads to a significant reduction in the unnatural components of residual noise. Results from simulations as well as evaluations confirm that enhanced nonacoustic sensor speech is more pleasant to listeners than speech produced by traditional spectral subtraction algorithms. This suggests that the proposed method satisfactorily reduces whole-frequency and musical noises and produces good speech quality.