Voices can make the campaign world. What do I mean by that? Well what is the first thing you think of when you think of Braveheart, Zorro, Inigo Montoya, Fezzek, Conan, etc? I’ll bet that you think of a quote and you think it in your head as they would say it including their manner of speech and their accents.
While every player intimately knows their characters - how their characters will react, think, look and sound, you are the DM and it is your job to try to be the rest of the world. If that mountain dwarf Grendel of the Far Clan is going to have a gruff accent with a Scottish undertone, it is up to you to convey it in your voice. If you want your players to role play their characters then you should expect that they will want you to roleplay your npcs.
There are basically two schools to using your voice – Accents and Voice Modulation. That is what I am calling them here though they may have specific names or even official names elsewhere.
“Go away you thundering silly person or I shall taunt you a second timea!” – Monty Python, Holy Grail
An accent is when you change your voice to match or resemble a different pattern of speech than your own. For instance, most American have never been to Spain but we’ve all seen Zorro (sorry Spanish readers) and should be able to adept a Spanish accent fairly easily for that Amnite priest. Likewise, we’ve seen Braveheart and could probably get away with some kind of variation of Scottish or Irish.
So what if you have a bad Scottish accent or a passing English one. The point is to ham it up a bit to keep the npcs memorable. As a point for the DMs it also helps to develop accents because you are able to keep track of your npcs by their speech types.
I remember saying “who was that again?” once to a player who had a brief encounter with an npc shopkeeper that was apparently so memorable when they returned to the town several months in game-time later they remembered the shopkeeper’s distinct greek accent and gruff manner. I had forgotten but they remembered! It’s all about creating something that seems real!
“I am batman!”
The second school of voice is modulation. This is when you change your voice in pitch and in frequency to be something bigger, smaller or more or less intelligent sounding.
If the villain Marduark has a previous wound that causes him to speak like the villain from Highlander then you give him a gruff voice when talking in his character. See there are even multiple ways to ham up an encounter with an npc using your voice that requires no accents at all! Give it a try and tell me what you come up with!
In the end it is all a matter of how you use your voice. As with anything practice makes perfect. A good method for our troupe uses is to try to keep accents to a regional atmosphere and moderation to a minimum. That way the memorable ones will be truly memorable and not end up as a casting call for 100 voices.