function y = echo( x,k,d )

len     = length(x);

y  = zeros(1, (len+d));

for n=d:(len+d)
    
    if ((n-d) == 0)
       temp2 = 0; 
    else
       temp2 = k * x(n-d);
    end
    
    if (n > len)
        temp1 = 0;
        temp2 = temp2 * (-1);
    else
        temp1 = x(n);
    end
    
    y(n) = temp1 + temp2;
    
end