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:.