Research On Signal Processing Method In Laser Detecting Sound System

Laser detecting sound technology has been widely concerned and studied with non-contact and traceless features.And it has been applied in the fields of military,antidrug,criminal investigation and national security.Because laser monitoring equipment is often used in complex environments,The detected speech signal can be disturbed by noise introduced from the surrounding environment and transmission media,and internal electronic noise of the communication device.Therefore,it is significant to study the noise reduction method of laser detecting sound signal.In the thesis,firstly,the research background and status quo of laser monitoring technology and speech signal processing were introduced.The advantages of laser monitoring technology and the importance of the processing of speech signals were explained.Secondly,the basic principle of laser monitoring system was presented.The detection principle of the four-quadrant detector was analyzed and the noise types,sources and characteristics of the monitor system were analyzed.Then,the characteristics of speech signals and commonly used noise reduction methods were described.The wavelet threshold denoising method was selected to process the speech signal of the laser monitoring system.And an improved threshold function was proposed,the simulation experiment was designed to compare the noise reduction effects of several threshold functions,the experimental result shows that the improved threshold noise reduction method has a good noise reduction effect.The simulation experiment was realized through hybrid programming of Lab VIEW and MATLAB.The hybrid programming method combines MATLAB's powerful signal processing capability with Lab VIEW's abundant data acquisition and good interface design capabilities,and it increases programming efficiency.A photoelectric conversion module based on the four-quadrant detector was also designed including transimpedance amplifier circuit for signal amplification.A speech signal processing software system was designed,including the data acquisition and storage module and the wavelet noise reduction module.Finally,the experimental system was built and tested,A single frequency signal and a determined speech signal are respectively used as sound sources.The test result shows that the experimental system can achieve the functions of speech signal acquisition,storage and processing,The waveform and frequency of the output signal and the input signal keep the same.