Good and bad tone in Piano Playing

Realize, then, that you can only make tone by making the key move and thus convey speed to the string.
The greater the motion attained during key-descent, the louder the sound.
Note: Speed of the key, during descent, must not be confused with speed in the succession of the notes.
It seems unnecessary to point out that the quickest passages can quite well be played softly but I have had letters on this question.
Bad tone, and lack of control over tone, arises when the key is jerked down by a too suddenly applied impulse.
We see then that tone-amount depends purely on keyspeed, but control of tone and quality depends on how you produce that speed.

hammer-damper-action — The sustain pedal lifts the damper allowing the string to resonate instead of being silenced after the hammer strikes. This makes the other unplayed strings resonate softly, adding richer harmonics to the sound.

Obtain Correct Movements and Muscular Habits

Above all things, we must always remember that the ultimate purpose of our study is to obtain correct movements and muscular-habits to obtain command over musical-expression. With this purpose in view, we must, in playing, constantly feel key-resistance, so that we may thus be muscularly prompted to fulfill the requirements both of key and music. Good tone-production can in fact be defined by means of the following thought process:
We must allow key-resistance and musical-sense to

prompt us easily to move each key at requisite speed and increase of speed,
to a definite place in time and key-descent.