- I can hear a human voice.
- I can hear the human voice.
- I can hear human voice(s).
In #1, I can hear a voice which belongs to some individual person, and is not the voice or call of any other kind of animal. In #2, I'm stating that I have the ability to hear the voices of humans in general. In #3, I find myself hearing the sound of some human voice, from one or more people, as I might hear wind or smell food.
In this last sense, human voice is like bird song: it's sort of an abstract substance. Say I go into a cafeteria, where I'm surrounded by the sound of voice, then I hear a voice and turn around to see my friend calling me, whereupon I sit with him and we discuss my research of the voice.
If you want to make general statements about the vocal abilities of humans, use the human voice.