Question

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

Answer 1

Two sounds are usually distinguished by their pitch and loudness. But for recognizing a person on the basis of his voice, we distinguish him on the basis of timbre which is unique for each source of sound.

Complete Answer:
When sound is produced from two different sources, in general we are able to distinguish them on the basis of their two characteristics; loudness and pitch. We either differentiate two sounds either on the basis which one is louder, or on the basis which one is higher or lower.
We know that the loudness of a sound is a measure of its amplitude, which the pitch of a sound wave is a measure of its frequency. A sound having more amplitude is louder. Also, a sound wave having more frequency has more pitch.
But what if the two sound waves have equal amplitude and frequency? In this case both the sounds will be equally loud and higher, and the two sounds are said to be in the same Note. Let’s take an example of a violin and a flute being played on the same Note. We know from our common experience that although when the two sounds from violin and flute are equally loud and high, we are still able to distinguish them.
The property which enables us to distinguish two equally loud and high sounds is known as timbre. The timbre is the quality, or the color of a tone. It enables us to distinguish between the same Note sounds produced by different musical instruments. Through timbre, we distinguish the sounds on the basis of their smoothness.
Similar to the case of musical instruments, every person’s voice has a different timbre which enables us to recognize him without even seeing him.

Note:
Timbre of a sound is different from other sounds due to its unique shape. A sound is basically a superposition of several different harmonics. The timbre is different as a result of this unique superimposition of harmonics.