I don't have problems recognizing the key of a particular song. It is usually the beginning chord or the last chord. That is not my problem.

My problem, is lets say someone is singing a tune and then without a keyboard, I cannot determine which key it is. Right now to determine a key I have to get in front of an instrument, push a few keys to find that key because the keyboard has a perfect pitch. And I don't. I can play a tune in a keyboard perfectly and memorized all the chords in it but then when someone sings it, I cannot determine which key the person sings. Does anybody get it ?

In other words, lets say I usually plays a song in a key of C. If someone sings in a key of D, I would not be able to tell without using an instrument and actually pressing the keys, what key the person sings.