Abstract
A millimeter wave (MMW) radar sensor is employed in our laboratory to detect human speech because it provides a new non-contact speech acquisition method that is suitable for various applications. However, the speech detected by the radar sensor is often degraded by combined noise. This paper proposes a new perceptual wavelet packet method that is able to enhance the speech acquired using a 94 GHz MMW radar system by suppressing the noise. The process is as follows. First, the radar speech signal is decomposed using a perceptual wavelet packet. Then, an adaptive wavelet threshold and new modified thresholding function are employed to remove the noise from the detected speech. The results obtained from the speech spectrograms, listening tests and objective evaluation show that the new method significantly improves the performance of the detected speech.
Highlights
Speech signals carry a great deal of information that is essential for effective human communication
Speech time domain waveforms and spectrograms constitute a well-suited tool for evaluating the quality of speech because they can be used to evaluate the extent of the noise reduction, residual noise, and speech distortion by comparing the original radar-detected speech to the enhanced speech
Listeners were instructed to evaluate the intelligibility of the original radar-detected speech and the enhanced radar speech based on the criteria of the mean opinion score test (MOS), which is a five-point scale (1: bad; 2: poor; 3: common; 4: good; 5: excellent)
Summary
Speech signals carry a great deal of information that is essential for effective human communication. It is well known that speech can be transmitted through air and can be detected by traditional acoustic transducers, or air-borne microphones that convert acoustic energy into electrical energy [1]. Other methods to detect speech signals include using bone conduction microphones, which are transducers that detect vibrations conducted through bone [2,3], and optical techniques, such as light waves or lasers [4]. While all of these methods are commonly used, they do have some potential limitations. The details of the optical materials in use are often difficult to obtain [6]
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