Align two signals using correlation

align.m

function [ao, bo, offset, y] = align(a, b)
% align two signals a and b
% ao and bo are aligned ones with same length
% y is the correlation xcorr(a, b)
% a_ind + offset -> b_ind
% if offset >= 0, cut a, else cut b

an = length(a); bn = length(b);

N = max(an, bn);

y = xcorr(a, b); 
% y(i) = Rxy(i-N) -> a(n+i-N) ~ b(n) if i >=N, 
% y(i) = Ryx(N-i) -> b(n+N-i) ~ a(n) if i < N

[yy, ii] = max(y);

offset = ii - N;

if offset >= 0 % offset for a: ii - N
    ao = a(offset + 1 : end);
    if (length(ao) > bn), bo = b; ao = ao(1:bn); 
    else bo = b(1:length(ao)); end
else % offset for b: N - ii
    bo = b(-offset + 1 : end);
    if (length(bo) > an)
        ao = a; bo = bo(1:an);
    else
        ao = a(1:length(bo));
    end
end

end