探地雷达信号去噪问题

vivid920

x=load('zy.txt');
[m1,m2]=size(x);
for l=1:m1
    for k=1:m2;
        if x(l,k)>1000
            x(l,k)=1000;
        elseif x(l,k)<-1000
            x(l,k)=-1000;
        end
    end
end
n=m2:-1:1;
for l=1:m1
    y=x(l,:)+400*(l-1)+50*randn(1,4096);
    plot(y,n),axis tight; hold on;
end
hold off
figure(2);
y1=zeros(m2,m1);
for b=1:m1
    [c,l]=wavedec(y(:,b),3,'sym4'); %分解原始雷达信号
    [thr,sorth,keepapp]=ddencmp('den','wv',y(:,b));
    y1(:,b)=wdencmp('gbl',c,l,'db1',3,thr,sorth,keepapp);
end
for l=1:m1
    plot(y1(:,l),n);axis tight;
    hold on;
end
hold off

我对y加入了50*randn(1,4096)的噪声，然后用小波默认阈值去噪方法进行去噪，用了上面的代码，但是结果不对，请问是怎么回事？
详细数据可见http://forum.vibunion.com/thread-64729-1-1.html