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机械师2014

新虫 (小有名气)

[求助] MATLAB傅里叶变换 位移频响和速度频响差别在哪

实验采集到的离散的输入位移信号xi(t),输出位移信号xo(t);方法一:对输入和输出利用fft()进行离散的傅里叶变换后,求得系统的频响H1=xo(f)/xi(f);

方法二:先对xi(t)和xo(t)进行差分得到vi(t)和vo(t);然后利用fft()求出频响H2=vo(f)/vi(f);
为什么得到的H1和H2不同?


附:傅里叶变换程序
dt=0.002;
fs=1/dt;
N=length(xo);
Y2=fft(diff(xo),N);
mag_y2=abs(Y2)*2/N;
f=0:fs/N:fs*(N-1)/N;
magy2=20*log10(mag_y2(1:N/2));
figure(2)
plot(f(1:N/2),magy2)

求速度程序:


for i=1:length(xo)-1
    vo(i)=(xpi(i+1)-xpi(i))/0.002;
end
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