Yes, a pianist can control the " sound quality " BUT here is a matter of
physics (of course talent is always involve in it.  this is a fundamental
thing),rationality, and sobriety.  As close your fingers play the keys,you
avoid the "noise " of fingers Knocking the keys.This is a first thing to
take into consideration.  Then (specially in fortissimo passages), once you
press the key, you don't need to press it any more.  It is unnecesary,and
increase tension,and when the brake (sorry i don't know the name of this
piece of the mechanism),brakes the Hammer,in a very strong way,you just
remove all the neighbors close to the key you are pressing,and it create a
virtual sound effect(it is scientifically proved).  When your stroke is too
strong,and instead to liberate tension suddenly, you continue to press
very strong,the amount of miliseconds the hammer is in contact with the
strings,increase dramatically,and you can traduce it in "bad quality
sound".  All this kind of problems are bigger in louder sections.  For a
very "perlee"(articulate sound),you don't need to lift fingers, here the
important thing is to play asclose as you can to the keys, but leaving as
soon as you can the finger wich already played the last note.  It's a kind
of "scape" action.  On the contrary side:  To play legatissimo,you have to
hold for just a second fraction the (but just a very small fraction)note
you already played before.  Well those are a very few things on it.This
topic unfortunately is very extense, and cannot be completed in a E- Mail
way.  Good luck.

Gerardo:.