matlab实现小波降噪，求解

处理后的波形有畸变，尤其是在纵坐标0附近，原始信号纵坐标0时是“零休”状态，怎么能报这个特征保留下来

lst = reader('lst.txt');
sa = zeros(length(lst) - 1,5);
for ii = 1 : length(lst) - 1;
data = load(lst{ii});
fprintf('%s\n',lst{ii});
current = data(:,2);
[c,l] = wavedec(current,3,'db4');
[THR,SORH,KEEPAPP,CRIT]=ddencmp('den','wp',current);
[XC,CXC,LXC,PERF0,PERFL2]=wdencmp('gbl',current,'db4',3,THR,SORH,KEEPAPP);
subplot(2,1,1);plot(current);title('原始信号');
subplot(2,1,2);plot(XC);title('使用分层阈值降噪后信号');
per = norm(XC)/norm(current);
err = norm(XC-current);
figure; plot(current,'r');
hold on;
plot(XC,'b');
end

这是程序