Keyboard expression often shortened to expression is the ability of a keyboard instrument to respond to the dynamics of the music or change the tone of the sound in response to the way that the performer depresses the keys of the musical keyboard. Keyboard expression types include velocity sensitivity, which responds to how hard or fast the keys are pressed; pressure sensitivity, which responds to the force with which a key is held down after the initial impact; and displacement sensitivity, which responds to how far down a key is depressed. Different keyboard instruments offer a range of different types of expression. Acoustic pianos such as upright pianos and grand pianos are velocity sensitive. Baroque-style clavichords and professional-level modern electronic keyboards are pressure sensitive; the degree that the performer is pressing the key after the initial strike will produce effects such as vibrato or swells in volume. Tracker pipe organs and electronic organs are displacement sensitive; if the keys are only partly depressed, a quieter tone is produced.