Many synthesizers (especially softsynths) map changes in sound to velocity, that is, how hard you hit the key. Hitting the key harder makes a different sound (e.g. layers more samples) than hitting it softly.
Many synthesizers (especially softsynths) map changes in sound to velocity, that is, how hard you hit the key. Hitting the key harder makes a different sound (e.g. layers more samples) than hitting it softly.