Research On Broadband Acoustic Monitoring System

In a complex environment,the acoustic information frequency band covers a wide range,and the human ear is limited in the frequency range of sound perception.Some infrasound and ultrasonic acoustic information can not be obtained by human.Therefore,the related research on the broadband acoustic monitoring system is carried out to replace the human ear for acoustic monitoring.In consideration of the high precision requirements for acoustic information acquisition,this paper adopts the structure of Sigma-Delta ADC,and uses the oversampling technology of Sigma-Delta modulation and the principle of noise shaping to obtain pulse density modulation Pulse Density Modulation(PDM)data with high signal-to-noise ratio.Then it passes through a digital decimation filter to achieve downsampling while filtering out the high-frequency components of quantization noise,and finally the conversion of PDM data to Pulse Code Modulation(PCM)data is completed.Sigma-Delta modulation requires a very high oversampling rate.In recent years,some chips have designed two additional CPUs in order to improve the problem of insufficient control of high-speed external hardware,namely Programmable Real-time and Industrial Communication Subsystems(PRU-ICSS).A PRU-ICSS has two Programmable Real-Time Units(PRU),this article will use PRU with PDM microphone to complete the pulse density modulation of acoustic information.The digital decimation filter is mostly constructed by FPGA,and this article puts the digital decimation and filtering link in the CPU.Firstly,the digital filter bank is simulated and analyzed by MATLAB software,and a three-level filter structure of CIC filter,half-band filter and FIR filter cascade is designed,and the input signals of 1024 k Hz and 4000 k Hz are designed and simulated respectively by using this structure.After 64 times downsampling is achieved,the passband cut-off frequencies are about 6.5k Hz and 26 k Hz respectively,the passband ripple is 0.1d B,and the stopband attenuation is 80 d B.Then it provides a data uploading method,using TCP protocol with wireless transmission and wired transmission to upload the data to the host computer stably.Finally,a simple TCP protocol client host computer is designed using the Qt framework to complete the data receiving function.After the single-microphone monophonic test,the acquisition module can collect data stably and accurately,which can verify the feasibility of PRU with PDM microphone to complete the task of acoustic information acquisition.The data after digital extraction and filtering has an ideal signal-to-noise ratio and can be sent to the upper computer through the transmission module to provide a data source for subsequent related algorithm processing.