I provided the male voice narration over video footage of Mediterranean ecosystems for an "online virtual field course." This was an 'extra feature' provided with the university textbook First Ecology by Alan Beeby and Anne-Maria Brennan (Chapman & Hall, 3rd edition 2008).
None. My voice is entirely natural.
Whilst I've always been quite well-spoken, I had not considered the possibility of voice overs until a stranger overheard me ordering a round of beers in a pub and told me it would be a "crying shame" if I didn't use my voice for something like this. After a few more, similarly positive, comments over the intervening years, I decided I ought to give it a try!
Shure SM58 via XLR into a Behringer Xenyx 502 mixing desk (with 2-band EQ mic preamp), stereo output from which into a Creative Audigy 4 soundcard. Recording software is Cakewalk Home Studio, allowing for editing and some basic effects (e.g., EQ, compression, reverb).
My background is in science (currently working for a PhD in atmospheric spectroscopy), which I feel may give me an advantage dealing with scripts for scientific or technical projects.