function cfo_fine_eval(f, kn)

Kdown = 4;
fs = 48000/Kdown;

N = 1024/Kdown;
K = 100;
n = (0:K*N-1)';

phi = pi/2;
x = cos(f/fs*2*pi.*n + phi) + kn*randn(K*N, 1);

Xlast = [];
phi_x_ = [];
phi_z_ = [];
Zm = ones(N, 1);
for k=1:K-1,
    xp = x((k-1)*N+1:k*N);
    X = fft(xp);
    if (~isempty(Xlast))
        Z = Xlast .* conj(X);
        [v, bin] = max(abs(Z(1:N/2)));
        phi_x_ = [phi_x_ 0.5*angle(X(bin))/pi/N*fs];
        phi_z_ = [phi_z_ 0.5*angle(Z(bin))/pi/N*fs];
    end
    Xlast = X;
    
end
df = -mean(phi_z_)
f_est = (bin-1)/N*fs + df

figure(1)
plot(abs(Z)); grid;

figure(2)
plot(phi_x_); grid; ylabel('phi_x');

figure(3)
plot((bin-1)/N*fs - phi_z_); grid; ylabel('d_f');