Over at Bookends, Gina Robinson has some important things to say about finding your voice.
Personally, I don't think that writers necessarily have only one voice. Some do, like Isaac Asimov or Jack Kerouac or Raymond Chandler. Some don't. For instance, I would argue that Sylvia Louise Engdahl has three distinct voices in Enchantress from the Stars, each as beautiful and worthy as the others.
Likewise, each of us has many voices we use in our daily lives: parent, employee, supervisor, child, parishioner, confidante. Why would we not have many voices as writers?
It's similar to the difference between a character actor and ... blagh, I can't find the opposite term... an actor with range? A "character actor" plays the same kind of roles, over and over and over, like Adam Sandler or Gary Cooper. Other kinds of actors are much harder to pigeonhole, like William H Macy or Peter Ustinov.
Now, admittedly, I am a beginner in terms of authorship. However, I think of voice more often as finding the voice of a particular character or story, rather than my voice. But what Gina Robinson says is very important, because it is a sign to finding which of your natural voices will work for your target audiences.
Go there. Enjoy.