So far I have: V=Acarriersin(2∏Fcarriert) (1+Cmodsin(2∏F1t)+Cmodsin(2∏F2t)) which I think is pretty close to correct. Where: A is amplitude, F is freq, t is time, Cmodis the coefficient of modulation, i.e. 1=100% modulation. I can find plenty of websites offering 1-tone AM, but not 2 or more tones. You actually have to mess with Cmod, because if you use 1, you get 200% modulation with two tones... I think.