Harry Walsh, a freelance copywriter who once worked for Ogilvy & Mather, put it this way for direct marketing:

The tone of a good direct mail letter is as direct and personal as the writer’s skill can make it. Even though it may go to millions of people, it never orates to a crowd but rather murmurs into a single ear. It’s a message from one letter writer to one letter reader.

For audio, the tone should be as direct and personal as the scriptwriter’s skill can make it. Speak from one person to another, from your mouth to the listener’s ear.

(Hat tip: Denny Hatch at Business Common Sense.)