function [ alpha ] = alpha1( x, y, N, n )
%ALPHA1 Given an input signal x, an output signal y and the delay of the
%echo N, returns alpha, the magnitude of the echo.
L = length(x);
if mod(L,2)==0
    c = L/2;
else
    c = (L+1)/2;
end
n = c+N+1;
alpha = (y(n)-x(n))/x(n-N);