So, to fix the features of a timbre we can consider the current harmonics, but these are inadequate informations.
We must consider the envelop ADSR, especially attack kind, harmonics development in time and others noise-sounds, as noise attack, for example.
Another important thing is the body that produce the vibration. The sound of a piano is very different if I strike its strings with hammers or with fingertips, or something else (John Cage docet).
There are always:
- an exciting body
- a resonant body (harmonic case).
The relation between them creates our timbre perception.
The theoretic rule tell us that in a harmonic sound one overtone component has lower amplitude than the previous one,
but really it is not always thus.
In this network many people use voice in several ways, so I write something about vocal resonance and vocal formants.
Vocal tract is an harmonic case very special: it is not rigid. It is made up of many little changeable cavities in which acoustic energy develops itself.
Resonance cavities are full of air:
- when a sound wave collide with air, air vibrates
- so, in function by the shape and structure of the vocal tract in that exact istant, sound will undergo the increase of some harmonic components (and not others), fixing exact formantic zones
Formant = acoustic energy concentration in a some frequency band
The resonator object is not the resonance cavities or the vocal tract, but the air included into them.
Sound of vocal folds is like a weak drone and it transform and develop itself by the over-glottical cavities (vocal tract). I say over-glottical and not under-glottical cavities because the way of the air, from lungs to vocal tract, is vertical, from down toward upper resonance cavities.
All that is under vocal folds can not resonate because it is collide by no kind of acoustic energy.
Acoustic energy can't exist under vocal folds.
Air from lungs to vocal folds is of not-vibrating kind, so our chest can't be a resonator.
Vocal coaches and singing teachers (only few, unfortunately) tell about this as a resonance sensation.
Resonance sensations are fixed by skeletal and muscular vibrations, and their amplitude is really very slow. They are only sensations.
All that is under our vocal folds can't be amplified because it is not in resonance.
In case it is in consonance, and this is very different.