Grumpy_Mike:
An amplifiers distortion specification has nothing to do with how much or little distortion is on the input signal. An amps distortion spec is based on only the distortion added by the amplifier.
Yes I don't disagree with that.
But the point is that the more distortion is on a signal, however it got there, changes the power output of the system.
No I don't see that either. Power output and distortion output are two separate measurements dealing with different attributes of a audio output signal. Distortion is simply the deviation of output signal relative to input signal (minus gain). Power output is simply the product of voltage and current of the output signal. Specifying power at a maximum allowed distortion value is just a truth in advertisement method so one can make sure they are comparing apples to apples for two different manufactures power claims.
Lefty