What allows us to distinguish between two different voices even if they're singing the same note?

Question

I love Freddie Mercury. I love Robert plant. I once heard Robert Plant sing a Freddie Mercury song at a tribute concert. Plant sang the song beautifully, but it was obvious that the song was different from the original -- it was obvious that Freddie Mercury was not singing the song.

From what I understand, sound can be described as a sinusoidal wave. Now, based on the assumption that both singers can hit the exact same pitch with the exact same intensity, what other parameter can we modify in a sinusoidal wave that would allow us to distinguish between the two voices?

Answer 1

No voice sings in a "pure tone", i.e., while the voice is in tune, the sound signal is composed of various harmonic frequencies. This gives you the "color" of the voice, and that makes the two voices distinct.