In theory, a piano tuned to perfectly even intervals between each note -- so that the frequency of each note is exactly 2 raised to the 1/12th power times the frequency of the note just below it (1.05946... times), for the mathematically inclined -- would show no difference between keys; they'd all sound the same, just transposed (which a few golden-eared folks might be able to hear). However... the overall sounds would be dull and lifeless.Most well-tuned pianos which I have played do seem to have different characteristics from key to key. But... maybe I am fooling myself?