Playing two or more sounds together to achieve a fuller, richer sound. Many modern keyboards and synthesizers have layering functions that allow you to create a composite sound from several individual components. Layers can also be used to allow a sound to change in real time based on velocity or some continuous controller input, which provides a simple mechanism to create more expressive and realistic sounds. It is quite common, for example, to have the same instrument sampled at three different dynamic levels to capture the unique timbre of each. Those samples can then be applied to layers that switch or crossfade into one another based on the player’s velocity.