Reactive and Adaptive Sound

Reactive sound is any sound that reacts to the player’s direct input. This, for example, can be anything from a player shooting a gun, or punching an opponent in the face in a fighting game.
Adaptive sound is any sound that reacts to the game state, such as background noises such as NPC’s mooching about or environmental sounds such as a bird singing in a rainforest, or music playing automatically at the start of the game.

In the Flash game Portal, we have several examples of adaptive and reactive sounds.

Adaptive – At the start of the game and during levels music will start automatically, the player has no direct control over this.

Reactive – By making your character jump, you yourself are causing the jumping sound directly by pressing a button.

Reactive - Using the titular portals will directly activate a sound, as will jumping through the portal and emerging at the other end.

Another Flash game that has a number of examples of adaptive and reactive sound is the popular title Alien Hominid.

Adaptive - Again, the music is not directly caused by the player’s actions.

Adaptive – The sound of enemies shoot will automatically occur, and is not caused by the player’s actions.

Reactive – The sound of the player’s gun being fired is caused by the player directly.
Reactive – Enemies scream because they have been set on fire, this is directly caused by the player.

Examples of reactive and adaptive sound in film, taken from a scene from the film The Dark Knight.

Adaptive – music, the people on the screen have no direct involvement with the inclusion of the soundtrack.

Reactive – Sound is caused by a shotgun blast from one of the characters on screen.

Adaptive – Characters quietly speaking to one another in the background, this is not directly caused by the central character we are watching on screen.