Whether you're exploring epic realms with Dungeons & Dragons or pursuing the horrific unknown with Trail of Cthulhu, whether you're a new Gamemaster or a honed expert, you probably spend a fair amount of time describing what the players' characters see and hear. But what about what the players themselves hear? What about the soundtrack to your RPG campaign?
If you want a more cinematic experience when running your favorite RPG, do what movies and videogames have been doing for years: Use music to add a new dramatic dimension to the scene.
Music can heighten the theatricality and deepen the immersion in a storytelling game like an RPG. It saves you time and provides an undercurrent of atmosphere even when your game temporarily devolves into in-jokes or rules debates. It works like the music in your favorite movie or videogame, except the music is never (or almost never) composed specifically for the game you're playing. To select and play the right tracks to give your game new ambiance and attitude, you, the DM, must also become you, the DJ.
First, some terms. Film music comes, roughly, in two types: source music and score. Source music is music that exists within the fictional world of the story, whether it's being played by a musician character on screen or echoing from a tinny radio in the hero's car. If the characters can hear it, it's source music. You can also call it diegetic music, because it exists in the diegesis, the fictional world of the story.
The score, on the other hand, is the music we in the audience hear but that does not literally exist in the world of the film; it's the music composed for the film. Darth Vader doesn't hear "The Imperial March" when he's striding the deck of his Star Destroyer, but we do. This is non-diegetic music.
I use these same terms when talking about the music I assemble for my RPG campaigns. The score is anything the players hear but the characters can't. The source music is anything the characters can hear that I play out loud for the players, too.
If I just say to my players, "Beethoven's 'Für Elise' is playing on the loudspeakers in the derelict alien spaceship you've boarded," it's just a reference to the music. If I actually play "Für Elise" on the speakers in my living room while our characters explore a spaceship where that music is playing, that's source music.
To play the right cue you first have to find the right cue. That requires an understanding of how you're going to use the track in actual play. It also requires a selection of tracks from which to choose.
Some great soundtracks come from mediocre movies and games. I've often used bits of score from movies and games I've otherwise not enjoyed because the music suits something I'm trying to do with the atmosphere of my home game. (I've never even played Lair but I've used its epic and textured musical score, by John Debney and Kevin Kaska, in countless D&D sessions since I found it.) Such soundtracks have the advantage of being less familiar to my players. Something as familiar as John Williams' iconic theme for Darth Vader's evil empire - "The Imperial March" - feels like parody when it's used outside of Star Wars. I prefer to use music that's appropriately moody yet not immediately familiar, because it works for atmosphere without reminding the player of someone else's imagery.