Hi Eldartford, sure. All amplifiers have what is called Propagation Delay, which is the period of time that it takes a signal to propagate from input to output. This propagation is caused by the risetimes of various internal stages and is not 'the speed of light' which is a common misconception.
In fact the propagation delay of any audio amplifier can be easily measured on any decent oscilloscope.
The propagation delay is a constant; it is not a problem unless there is negative feedback. Lower frequencies that are fed back tend to arrive much closer to the actual time that they need to be there (although the propagation delay means that they will *always* be a little late). As frequency increases, this delay has a more profound effect, essentially introducing a ringing effect.
This ringing is easy to understand if you think about a positive-going pulse of short duration being applied to the input. The amplifier responds to it and the feedback applies an inverted version of the pulse at a lower amplitude back to the input. By this time the original pulse is either gone, or nearly ended. Now the amplifier has to amplify the negative-going pulse; this process goes on as a ringing phenomena that dies out, although wider-bandwidth amplifiers often have to have filters in the feedback network to prevent this phenomena from causing oscillation, particularly if the amplifier exhibits phase shift at higher frequencies!
The result is low-level odd-order harmonic generation, usually the 5th, 7th and 9th are the greatest concern. It does not take a lot- the human ear so sensitive to odd-ordered harmonics that hundredths of a percent will audible (as a hardness or harshness) when a band of frequencies is being amplified.
Conversely, the human ear does not object so much to even-ordered harmonics. These create 'warmth' and 'lushness' but are a coloration nonetheless. Audiophiles have words to describe harmonic distortions of both types.
odd ordered descriptive terms: hard, harsh, clinical, overly-detailed, chalky or chalky-white, brittle, etc.
terms for even-ordered harmonics:
warmth, bloom, lush, fat, muddy
-as distortion increases.
