I have a digital piano that has a relatively realistic sound at home, so I played some notes to see how they look in the Timbre app.
The first thing I noticed was that the picture changes as the note sustains. When the note is started, there are many more harmonics, but as the sustain continues, the harmonics settle down with everything but the note, the 5th, and the major 3rd fading away.
Here’s C2. A nice low and rich note.
Here’s C3. The early harmonics are more numerous than the later sustain.
Here’s C4; middle C. The timbre is noticeably more pure, and the picture seems to reflect this.
I’ll be interested to try this with a proper analog Piano.