Good point, John. The only response I can come up with is that auditory memory is very short. So, when you return to the speakers that were playing in your absence, you are comparing what you are hearing to your IMPRESSION of what you heard earlier, rather than what you actually heard. That doesn't rule out the possibility that the speaker changed in your absence, but it doesn't confirm that it did, either.

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton