Hi all, I understand the concept of group velocity when applied to superimposed sine waves of the same amplitude, and even when applied to wave packets (in which case you get the well-known expression ∂ω/∂k). My question is what happens when you add two sine waves of different amplitudes? So something like: y(x,t) = A1Sin[k1x-ω1t]+A2Sin[k2x-ω2t] I tried to work out whether the concept of group velocity even has a meaning here, and if so, what it would be. If the amplitudes were the same, one can use trigonometric identities to express the wave as the product of an envelope and something else. Then, the envelope can be seen to travel at the velocity Δω/Δk. But, again, I don't know how to proceed if the amplitudes are not the same. Any comments are very appreciated.