% 裝載噪聲chirp信號(hào)
load noischir; x = noischir;
% 使用sym6對(duì)信號(hào)進(jìn)行5層小波包分解
wname = 'sym6'; lev = 5;
tree = wpdec(x,lev,wname);
% 由第1層高頻系數(shù)估計(jì)噪聲的標(biāo)準(zhǔn)差，結(jié)點(diǎn)索引號(hào)為2
det1 = wpcoef(tree,2);
sigma = median(abs(det1))/0.6745;
% 使用wpbmpen選擇閾值
alpha = 2;
thr = wpbmpen(tree,sigma,alpha)
% 上面的閾值，軟閾值處理，保存低頻，使用wpdencmp進(jìn)行信號(hào)降噪
keepapp = 1;
xd = wpdencmp(tree,'s','nobest',thr,keepapp);
% 畫(huà)出原始信號(hào)和降噪后的信號(hào)
figure(1)
subplot(211), plot(x),
title('原始信號(hào)')
subplot(212), plot(xd)
title('降噪后信號(hào)')