Thank you very much! But why is y3:
x[3] multiplied with h[0]+ x[2] multiplied with h[1]+x[1] multiplied with h[2]
and not:
X[1] mutiplied with h[2] + X[2] multiplied with h[1] + X[3] multiplied with h[0]
for example?
Do you think that X is reversed, instead of the impulse response?