If you are interested in singing, you probably have one or more favorite singers. A large part of what attracts us to a particular singer’s voice is the way it sounds, rather than the notes used.
Every singer has an individual sound because everyone’s anatomy is slightly different. Just as each person has a different height, weight, arm length, coarseness or fineness of hair, skin tone etc., we all have slightly different shapes, sizes and thicknesses of the parts of the body involved in singing. The lungs, windpipe, larynx, tongue, lips, and cavities in the mouth and behind the nose are all individual and combine to create a particular timbre (tonal quality or tone color).
All musical instruments have their own timbre, which makes them easy to distinguish from one another even when they are playing exactly the same notes. Listen to the following example which is played first on the guitar and then on the flute. Although they are both playing the same notes, they are easy to tell apart because each instrument has a different timbre.