The typical listener is probably a male (but might be a female), most likely under 30 (but might be over), and is almost certainly listening in a house (but might be in a car).When it comes to knowing its audience, the US-funded Radio Farda knows only two things for sure: that the audience is surreptitiously listening somewhere inside Iran, and that the Iranian government doesn’t want anyone to hear what a US-funded radio service has to say. How, then, does Radio Farda — which receives about $7 million in American funding and is hoping for substantially more as the US expands its push for democracy in Iran — decide what to broadcast?The answer can be found in an anonymous office building off Interstate 95 in Northern Virginia. There Sara Valinejad is about to click a computer mouse and determine what any Iranian with an AM or shortwave radio, or an Internet connection, will be able to hear the following day.‘‘In Iran, they don’t allow you to be happy,’’ says Valinejad, 30, who emigrated from Iran 10 years ago. Radio Farda, she says, is intended to do the opposite. ‘‘It puts you in a good mood when you listen to this radio station.’’Bert Kleinman, consultant to Radio Farda says, ‘‘The core of the mission is news and information’’ — in a typical hour, 16 1/2 minutes of programming is devoted to news — but ‘‘we were tasked to reach out to the younger generation there. And quite frankly, you just can’t do it with news.’’Valinejad as the person in charge of the non-news sifts through some 300 phone messages a day from listeners responding to the interactive feature ‘‘What Do You Think?’’ More than anything else, though, there is music. ‘‘Adult contemporary,’’ Kleinman says. Music with ‘‘a happy beat to it.’’ No hip-hop. No alternative. No rap.What makes it worth it, Valinejad says, is the idea of sending music into such a place. One thing she remembers from living in Iran is that love songs weren’t allowed, unless they were songs about love of God or Islam. So into Iran goes a Celine Dion ballad and eight or so other songs every hour on a route from Northern Virginia to Munich, then to a transmitting facility in Dubai, and then into Iran where the government tries to jam the signal and there’s no way to tell who’s listening at any given moment.David Finkel