load noisbloc
s= noisbloc(1:1024);
ls=length(s);
[cA1,cD1]=dwt(s,'db4'); 
A1=upcoef('a',cA1,'db4',1,ls);
D1=upcoef('d',cD1,'db4',1,ls);
subplot(2,1,1);plot(A1);title('低頻A1')
subplot(2,1,2);plot(D1);title('高頻D1')
A0=idwt(cA1,cD1,'db4',ls);
figure(2)
subplot(2,1,1);plot(s);title('原始信號')
subplot(2,1,2);plot(A0);title('重構信號')

[C,L]=wavedec(s,5,'db4');
cA5=appcoef(C,L,'db4',5);
A5=wrcoef('a',C,L,'db4',3);
D1=wrcoef('d',C,L,'db4',1);
D2=wrcoef('d',C,L,'db4',2);
D3=wrcoef('d',C,L,'db4',3);
D4=wrcoef('d',C,L,'db4',4);
D5=wrcoef('d',C,L,'db4',5);
subplot(3,2,1);plot(A5);title('低頻A5')
subplot(3,2,2);plot(D1);title('高頻D1')
subplot(3,2,3);plot(D2);title('高頻D2')
subplot(3,2,4);plot(D3);title('高頻D3')
subplot(3,2,5);plot(D3);title('高頻D4')
subplot(3,2,6);plot(D3);title('高頻D5')
figure(3)
A0=waverec(C,L,'db4');
subplot(3,1,1);plot(s);title('原始信號')
subplot(3,1,2);plot(A0);title('重構信號')
subplot(3,1,3);plot(s-A0);title('誤差信號')
err = max(abs(s-A0))