Introduced in 1983, MIDI is defined by midi.org as "a music description language in digital (binary) form." Its structure is performance based, telling the software what notes are played through a digital instrument (controller), the velocity of the notes and can also be used to direct other functions of the controller, such as the pitch wheel. Prior to the emergence of USB in 1995, connecting MIDI devices to a PC required an additional, often expensive sound card with MIDI "in" and "out" ports or adapters for less abundant serial and parallel ports built into the computer. USB cables are capable of transmitting MIDI signals without the need of additional hardware.
PC- and Mac-based soft-synth programs such as Cubase, Cakewalk and FL Studio have gained a wide level of popularity due to the convenience of having a full digital audio workstation at your fingertips, and using a MIDI controller to operate their many functions is something a great deal of users enjoy. Connectivity between USB and MIDI has made this more affordable and accessible than ever for musicians, allowing for instant plug-and-play of their favorite devices and for multiple controllers to be used within a single recording session.
MIDI/USB-based lighting control programs such as VenueMagic and LumiDesk now allow for full automation of stage lights at concerts, plays and other various live performances. Most stage lighting equipment is now created with built-in MIDI inputs, and what once required the synchronization of multiple expensive, standalone devices now can be done on one computer. The virtual stage visualizers included in the software also allow for composition of a full light show on-screen, giving the user the ability to fine-tune and rehearse their lighting display from home and without plugging in a single device.
The ability to connect a MIDI device through any USB port has also opened the door for both commercial and free learning software, such as Synthesia and Piano Wizard. Programs like these make learning how to play a piano more encouraging and entertaining by creating visual cues for the user and by using scoreboards, and allow for but do not require reading of sheet music. MIDI song files are also very small and are easily available on the Internet, providing the user the ability to import their favorite songs into these programs so they can learn to play along.
USB device drivers are now typically included with computers' operating systems, eliminating the need for an installation CD or download from the manufacturer. Though there are a few devices out there that require additional driver software for specific tasks, it is often not necessary. Most digital audio workstations will simply recognize a "generic MIDI controller," thus eliminating the need for tedious driver installation and also any risk of losing an installation CD.