top for tabletop units, typically contains a small screen or panel to provide information to the user. An LCD panel or an LED alphanumeric display may be supplemented with LED indicators to show the status of various features. In some models, LED indicators are embedded within a translucent button, so pressing the button shows its status on the button. There is usually a volume control, some types of buttons or knobs for selecting sounds and changing settings, and a power button. The front panel may also have a headphone jack, USB port, or another port for making connections. The smallest, simplest piano modules may have only a volume knob and a knob to select different piano sounds. The most complex synth modules may have a large number of knobs, buttons, and faders to control oscillators, filters, and amplitude settings. The rear panel usually contains 1/4 inch left and right audio outputs and one or more 5-pin MIDI inputs. Some units may have MIDI thru connections, which can be used to chain devices. Starting in the 2010s, some modules have one or two USB connections and can be connected to a computer (laptop, tablet, etc), to allow the user to use editing software to make advanced changes to settings or sounds. Advantages A sound module has the same advantages over a fully integrated instrument as does any system with a modularized design: Cost — a sound module is cheaper than a comparable instrument equipped with a controller. Space and weight — a sound module takes up less room and weighs less than an instrument equipped with a controller, facilitating transportation and touring. Portability - a performer going on tour can bring only their sound modules, so long as a MIDI controller (e.g., a MIDI keyboard) is provided as backline gear. Many professional studios have a MIDI stage piano on hand. Expandability — many sound modules can be expanded with sounds and memory. Troubleshooting – if a sound module in a rack case develops problems, just this one unit can be removed for repair or replacement, leaving the rest of a keyboard player's rig the same (e.g., other rack-mounted sound modules, power amps, etc.). Obsolescence cycles — when it becomes obsolete, a sound module can be replaced without changing a favorite controller, or vice versa. Notable examples Roland MKS20: Piano sound module used by many bands in the 1980s to early 1990s.