请教,有段代码读不懂,望高人指点下~

resid=dct(resid);
[a,b]=size(resid);
resid=[resid(1:50,:);zeros(430,b)];
resid=uencode(resid,4);
resid=udecode(resid,4);
resid=idct(resid);
noise=[zeros(50,b);0.01*randn(430,b)];
resid=resid+noise;