声学测量中的数据采集及信号处理基础知识.pps

声学测量中的数据采集及 信号处理基础知识,声仪科技 制作,声学测量流程图,灵敏度,激励声压1Pa(声压级94dB)时传声器输出电压 若灵敏度 50mV/Pa, 前置放大器电压范围 0-4V, 最大测量声压理论值,抗混叠滤波,抗混叠滤波器,Anti-aliasing filter designed with MATLAB,如果采集信号的带宽大于分析带宽，因此高于分析带宽的高频信号的信息就会由于采样频率低而加载到分析的频谱上。,混叠,通过设计一个低通滤波器实现,采样,什么是采样 采样率 采样间隔 采样精度 采样定理,什么是采样,采样就是把连续时间信号用一系列离散值来代替的过程。,采样率,单位时间（1秒钟）采样的个数 又称采样频率 fs,采样间隔 每采两个样本的时间间隔，也就是采样周期。 t=1/fs,采样精度,用二进制数来记录采样值. 每一位在采样电路中代表一个电平. 8bits=1byte 16bits=2bytes 24bits=3bytes 如果采样精度是24位，那么最小电平值,Nyquist 采样定理,采样频率应该满足至少大于分析频率的两倍,一倍采样率，结果是常数,原始信号：正弦波,1.5倍采样率，结果是低于原始信号频率的正弦波,两倍采样率，结果是与正弦波相似的锯齿波,多杯采样率，还原结果与原始信号相似,傅立叶变换,The Fourier transform is a generalization of the complex Fourier series (Spectrum),FFT,Fast Fourier Transform A fast algorithm of Discrete Fourier Transform,The number of time series and frequency spectrum series are equivalent,Window,analyzed signal is finite in length. If signal is periodic, a rectangular window with one cycle length will be enough For stationary random signal, special windows are adopted. Windowed signal is weighting of finite-length signal. In frequency domain. Multiply in time-domain means convolution in frequency-domain. The spectrum of window is used as impulse which sampling the signal spectrum . The properties of right window,Auto Power Spectrum (APS),Spectrum without any phase information,Cross Power Spectrum (CPS),Phase is difference of phase of X(w) and Y(w),地址：深圳市宝安区西乡海城路白金假日1106 电话传真网址：www.AAI-T E-mail:：,Frequency Response Function,Transfer function,地址：深圳市宝安区西乡海城路白金假日1106 电话传真网址：www.AAI-T E-mail:：,Coherence Function,coherence function to identify both excessive noise and which of the multiple signal sources are contributing to the response signal,地址：深圳市宝安区西乡海城路白金假日1106 电话传真网址：www.AAI-T E-mail:：,RMS Level,RMS level of continuous signal,RMS level of discrete signal,Average,The simple average for the j-th interval is equal to the sum of values from (j-N)-th to j-th intervals divided by the number of intervals, N. The exponential average is calculated according to the following formula:,地址：深圳市宝安区西乡海城路白金假日1106 电话传真网址：www.AAI-T E-mail:：