% 平滑降噪% FFT变换和小波变换clcclfclearlength_of_sig=128;x=linspace(0,2*pi,length_of_sig);% signal=5*sin(x)+2*sin(5*x)+randn(x);书上的这个是错的,随机数里的参数要求是整数raw=5*sin(x)+2*sin(5*x);signal=5*sin(x)+2*sin(5*x)+randn(1,length_of_sig);jiequ=16;transf=fft(signal);filter_transf(1:jiequ)=transf(1:jiequ);filter_transf(length_of_sig-jiequ:length_of_sig)=transf(length_of_sig-jiequ:length_of_sig);filter_signal=ifft(filter_transf);% before_hist=real(transf);% after_hist=hist(before_hist);% after_hist=histogram(before_hist);[xd1,cxd1,lxd1] = wden(signal,‘sqtwolog‘,‘h‘,‘sln‘,3,‘db3‘);[xd2,cxd2,lxd2] = wden(signal,‘sqtwolog‘,‘s‘,‘one‘,2,‘db3‘);plot(x,signal,‘k--‘)hold on;% plot(x,raw,‘r‘)‘无噪声信号‘,plot(x,filter_signal,‘b‘)plot(x,xd1);  plot(x,xd2);  legend(‘无噪声信号+噪声‘,‘FFT恢复信号‘,...    ‘小波1恢复信号‘,‘小波2恢复信号‘)% 从结果看来小波2和FFT效果都不错。