This post explores some dynamic uses of instrument layers, within video games.
Journey
In the game Journey, you’re a traveler in the desert, and you can meet another player. The solo instruments in the game's background music represent different ideas.
The harp and the viola represent the other player. And both of those instruments change volume, in the mix, depending on the distance from you to the other player. They are louder when the other player is near you, and quieter when the player is further away, and they are not audible if there is no other player.
This allows for a musical experience that is as dynamic as your game experience. The world is audibly sparser if you are travelling alone, and filled with melodic embellishments and counter-melodies if there is someone travelling with you.
This video highlights three different versions of in-game music that can occur, depending on whether you are alone, are with another player, or choose to release some cloth creatures.
A Short Hike
A Short Hike is an example I’ve heard about, though I haven’t played it myself yet.
There are different music layers common to certain parts of the map (e.g. some parts share percussion layers, and they share melodic layers with other different parts). They can subtly orient you, in your mental map of the main island in the game.
Laya’s Horizon
From a blog post by the devs of Laya’s Horizon with the sound/music designers:
Another obvious visual distinction was the different biomes. We split the island into four logical biomes, each having their own unique instrumentation. Basically, this also meant re-creating the composition for the main flight track 4 times — each time with different instrumentation. Upon entering a new logical biome, we would seamlessly switch from one instrumentation to another.
In the beach area you can hear a French Accordion and a Mandoline. Electric Guitar and Contrabass Flute in the dark cliff region. In the snowy biome Glockenspiel and Synthesizers take the lead to achieve an icy feel.