Voice of a friend is recognized by its :

The pitch and loudness of two sounds are usually used to distinguish them. However, in order to recognise a person based on his voice, we distinguish him based on timbre, which is unique to each source of sound.

The quality of a person's voice can be used to identify them. The range, weight, tessitura, transition point, speech level, and vocal registers of a person's voice are all important factors. Among the aforementioned phenomena, voice range and voice weight aid in the recognition of a person's voice.