Using the Hilbert transform is a better way to proceed than your
x2 = sqrt(x.*conj(x));
The above just gives the magnitude squared of each of the waveform values and that is not the envelope. At least probably not in the sense you mean envelope. To illustrate how the Hilbert transform does indeed extract the envelope, I'll give you a simple example with an AM-modulated wave.
Fs = 1000;
t = 0:0.001:1-0.001;
% 250-Hz sine wave modulated at 10 Hz
x = [1+cos(2*pi*10*t)].*cos(2*pi*250*t);
y = hilbert(x);
plot(t,x,'k'); hold on;
plot(t,abs(y),'b','linewidth',2);
plot(t,-abs(y),'b','linewidth',2);
If you know zoom in on parts of the waveform, you'll clearly see how the modulus of the analytic signal yields the envelope. Specifically, you see that the envelope oscillates at 10 Hz.
set(gca,'xlim',[0.05 0.35]);
set(gca,'ylim',[-2 2])
