Piano technique improvement on tonal quality is achieved by coordinating the muscles involved in piano playing, making adjustments and lots of repetition
Unlike building up speed which is a mechanical exercise, work on improving tonal quality is an artistic endeavour. Artistic work should not be turned into an exercise. Which is why I only delve into it, after I am done with building up speed so that I can dedicate my heart and soul into the effort without distractions.
Expectation is a form of distraction because it adds pressure to the effort. When working on tonal quality it is best to start absent of any expectation. What I usually do is to play my worse and proceed from there. Even the tiniest improvement is a success and deserves to be celebrated. Through continued consistency the tiny improvements compound into significant improvements after several months.
Take the phrase shown in Image 1 below for example. Initially I was only able to hit the correct notes to make sounds devoid of substance. With repetition from hours of practise each individual notes began to reveal its own shade of color, specifically in its volume, duration and nuance as I put in the effort to sharpen these characteristics. As a result a musical phrase is elevated to greater heights.
Repetition also brings with it the benefit of a deeper insight into the musical phrase. Because through it the brain creates neural pathways that pave the way for the piano student to play better with every attempt. I have also experienced noticing things I missed before such as tiny rhythmic errors or a note mistakenly read by accident therefore was able to correct them prior to a performance thus rescuing myself from a very public embarrassment.
It is tempting to finish a song as quickly as possible, to be honest a piano student does not have the luxury to take her time in learning a song. When I was taking lessons, my teacher demanded to see significant progress every week. But if you take the initiative to study the artistry in a composition when beginning to practise, the tedious task of repeated practise to become proficient gets easier and more engaging.
To do so, listen carefully to the tone, duration and rhythm of the sounds you are producing. Make the necessary adjustments to arrive as close as possible to the ideal result as written in the composition. Therefore you shall have to stay persistent in harmonizing the elements involved in the execution. Specifically tone production, rhythm, accelerations, decelerations and tempo.
Making adjustments means to make adjustment in your movement. Producing good tone requires the use of the bigger and stronger muscles that support the smaller and weaker muscles in the fingers. Which allow for the press of the piano keys to occur accurately and with clarity. It is a matter of coordinating the movement of the upper arms from the shoulder, wrists and hands where the stronger muscles reside to the fingertips touching the keys where accuracy is determined and controlled.
Practising coordination between the various muscles involved in executing a musical phrase on the piano is best done in small sections. For example a phrase can be divided into shorter parts such as 2 or 3 bars. Concentrate your attention on perfecting these small sections first, then another and connect them to erect a well played phrase.
Improving the quality of tone produced while playing the piano is an artistic endeavour involving creativity. Patience and time is needed for such work and a lot of repetition. Listen to how the tone sounds and make adjustment to arrive at the desired tonal quality. Adjustment are made on the motions of the arms, wrists, hands and fingers so that each of their muscles are properly coordinated to coax the ideal tone out of the piano.