This subject is a very complicated one.

I can see three major factors, or perspectives here.

1.  The physics in a piano, and the acoustic circumstances around the
piano.

Very important view, for example a persian carpet is absorbing high tones,
but reflecting frequencies in the bass.  Glass windows are absorbing bass
tones, but are reflecting treble frequencies...  (Horowitz once covered a
complete hall with carpets, to refine the acoustic ehavior of the room.
Only seldom pianists are affecting their tone in that way.)

2. The physical and biological conditions of the human ear.

The human hearing sense is more sensitive to higher frequencies, and very
less sensible to bass sound.  Each human ear is different according to
this frequency - selective sensitivity.  Due to the aging process, the
sensitivity to higher tones is getting less, bass tones are better heard
then.

3.  The personal, subjective reception of a tone.  Here the brain comes to
attention, because it is processing the impressions, and the in my opinion
most important factor: The soul.

I am not knowledged enough, to give very enlightening hints in this very
important subject, so many factors are working.  But i want to recommend am
important book:

   Music, the Brain, and Ecstasy
   by Robert Jourdain.

The german version is: Das wohltemperierte Gehirn.

Here all the factors are very well explained.

My problem with a good tone is the damper of the piano. I am afraid, that
the most powerful instrument to manipulate the overtone output is a superb
pedalling, in connection to a very well - balanced dynamic, which is very
well balanced from pppp to ffff.  This gives a very rich dynamic scale,
if we wont forget, that the mid tones and the bass secion are the most
"powerful" ones.

There is a melody line to shape, something two, or more, and a chord
structure, sometimes in the deeper secion, sometimes higher.  Highest
complication is not preventable.

One problem here: Chords in deep regions.

The reason: Overtones are for sure not only produced on the ground tone,
other tones are joining the band, which are not belonging to the harmony.
This problem is bigger in bass tones, because the bass strings are made of
more matter, which is in vibration, sending more energy through the
soundboard than a string in the treble section, which has hardly a weight
of 4 grams.  Thats why a not well - balanced chord in the lower region
sounds so muddy.  And thats, why a well balanced chord is so charming.
Horowitz, (and not only he!) is told to have been paying lots of attention
to well balanced chords.

I suppose only intense practicework and brave experimental behaviour can
help here, with much sensitivity.

There is one importance to practice right and left hand not only together,
but also each hand alone.

I suppose this helps to develop a fine pedalling.

And you know how it is: Pedalling is not pedalling.

If you use 100 % pedal, and no string is damped, there is extensive
overtone - development in your string -world.

If you play a quarter pedal, the extensive vibrations of bass strings are
blocked first, but the tiny movement of the treble strings is singing out
well.

Maybe one can use difficile pedalling as something like a "muddiness
filter", i am a bit lacking of experience here.  But i got very nice sounds
with minimalized pedalling.  Or, vibrato pedal.  Moving the pedal up and
down in very fast change, and with very small movement, nearly not visible.

There are for sure more factors, but i suppose, pedalling is the
iportant one.  Maybe Gould had success neatly without pedalling, but he
is different.  And with his Bach, there is to say that in polyphonic
music pedalling has quite another effect than in romantic music.

A pedalling, which could clear the music from beeing muddy, could mix
together different melody lines, and sotosay cause muddyness.  Maybe due
to this reason Gould sounds so brilliant.  Arthur Rubinstein said that
pedalling is the soul of the piano.

I have no more ideas which are worth mentioning here, i hope i only told
right things, and hope to be corrected if not.

P.S.: Dear new (young) list members, feel wellcome.  I am with 21 years
one of the younger persons here, and i am still alive, and no one threw a
mailbomb at me.  ;-) I also have the problem, that classcal music is seldom
listened to by the younger ones.  But my motive is, to change that.  The
charts are sometimes filled up with bullshit, (excuse me, but i cant help
here) and the only thing which our old masters could do is to rotate in
their graves like in a chicken - grill.

Norman, Germany