Any decent voice over agency should make a little effort to enlighten readers on this point.
You might only be at your begining as a voice actor or maybe you are simply curious. So, what do we call a voice over?
If we only consider the simplistic definition (hello Wikipedia), voice over is a narrative process, in audiovisual, that consists in interventions of a voice that don’t belong the scene.
Of course you have already heard a voice over, it can be the voice telling the thoughts of a character or this big punchy voice that comes out of the trailer for an all American blockbuster.
But apart from movies and shows, you will realize that you hear voice overs everywhere if you think of it. For instance when you are in a station and you are informed that your train is arriving. (You didn’t believe someone was actually saying this all day long, did you ?)
And of course, you also hear voice overs in video games, in telephone messaging systems, in e-learning modules, on TV, on the Internet, on the radio etc.
This is precisely why a voice over is genuinely an actor. It is not just an audio recording, it is a performance and even an interpretation, adapted to the message to be delivered. No wonder why voice overs are also called voice artists or voice talents.
But how to recognize a professional voice over?
First of all it is an actor able to adapt to the character. Of course s/he is not shy but does not play over the top. A voice artist can happen to work on very different projects as commercials, video games, TV shows, movies, IVR and many more.
In the end, each project is unique. To return to the question, a good voice over is not just a pretty voice, but a good interpretation. An interpretation that fits the context so well, that it would not come to your mind to even assess it…