function env = calculenv(x,Fe,f);
% calcul de l'enveloppe normalisee
%---------------------------------

N = 2*ceil(10*Fe/f);
b = fir1(N,f/Fe);
lx = length(x);
x2 = [x zeros(1,N)];
env = filter(b,1,abs(x2));
N = floor(N/2);
env = env(N+1:N+lx);
env = env/max(abs(env));
