Question

How is it possible to recognise a person by his voice without seeing him?

Answer 1

Sound quality or timbre describes those characteristics of sound which allow the ear to distinguish sounds which have the same pitch and loudness. Timbre is a general term for the distinguishable characteristics of a tone.
Timbre or tone quality is determined by the behavior in time of the frequency content or spectrum of a sound, including its transients which are extremely important for the identification of timbre.
The presence and distribution of these frequency components, whether harmonic or inharmonic and their onset, growth and decay in time, together with phase relations between them, combine to give every sound its distinctive tonal quality or timbre.