Ampliude and rate of change

[Kevin Weddle]

Is there any sort of modulation that uses the change of amplitude to give you a different rate of change. I know in AM the amplitude change is at the frequency of the message. But what about the amplitude of the signal itself. You know that whenver you gain a signal the amplitude increases and therefore the rate of change increases. Not by much when you consider the time of the sinewave. But it does.