will be played automatically in the tempo of the rhythm track. Many keyboards have an option to form on-bass chords, as well as many other complex chords. Demonstration: Most keyboards have pre-programmed demo songs. As the name "demo" implies, one usage of these pre-programmed songs is for a salesperson to use to demonstrate the capabilities of the keyboard, in terms of its different voices and effects. The demo songs can also be used for entertainment and learning. Some keyboards have a teaching feature that will indicate the notes to be played on the display and wait for the player to press the right one. Velocity sensitivity (also found under the keyword touch sensitivity in some manuals): While the least expensive keyboards are simply "on-off" switches, mid-range and higher-range instruments simulate the process of sound generation in chordophones (string instruments) which are sensitive to the speed (or "hardness") of a key press. Mid-range instruments may only have two or three levels of sensitivity (e.g., soft-medium-loud). More expensive models may have a broader range of sensitivity. For implementation, two sensors are installed for each key: the first sensor detects when a key is beginning to be pressed and the other triggers when the key is pressed completely. On some higher-end electronic keyboards or digital pianos, a third sensor is installed. This third sensor allows the player to strike a key and still sound a note even when the key has not yet come to its full resting position, allowing for faster (and more accurate) playing of repeated notes. The time between the two (or three) signals allows a keyboard to determine the velocity with which the key was struck. As the key weight is constant this velocity can be considered as the strength of the press. Based on this value the sound generator produces a correspondingly loud or soft sound. The least sophisticated types of touch sensitivity cause the keyboard to change the volume of the instrument voice. The most sophisticated, expensive types will trigger both a change in volume and a change in timbre, which simulates the way that very hard strikes of a piano or electric piano cause a difference in tone—as well as an increase in volume. Some sophisticated touch-sensitivity systems accomplish this by having several samples of an acoustic instrument note per key (e.g., a soft strike, a mid-level strike, and a hard strike). Alternatively, a similar effect