A Musical Instrument Digital Interface, or MIDI, harp is a harp which operates on the MIDI system and can be used to control a variety of other instruments or software programs. Some types of MIDI harp do not create any acoustic sound, sending the musical information to an amplifier or other MIDI enabled instrument through an electronic signal. Others produce both acoustic sound and MIDI signal. The vibration of the strings plucked by the player is sensed by the pickups, which are either attached to individual strings or spread across several strings.
Traditionally, harps are acoustic instruments, meaning that the strings produce an audible note when they are plucked. Technological advancement has made it possible to create electronic pickups which measure disturbances in the magnetic field created by the vibrating strings. This means harps can be made which do not produce any physical sound when plucked, but the vibration of the strings is turned into an electronic signal. The signal from the pickups can then be recreated by another device to produce the original note. These two factors are essential for the creation of a MIDI harp.
MIDI is a universal electronic musical language which enables many different instruments and computer programs to communicate with each other. There are 16 different MIDI channels in total, and each device is set to transmit and receive on one of these channels. The information sent through the MIDI signal tells the receiving instrument what note was played, how long it was played for, and how hard the note was struck. This basic functionality enables the user to play notes on a MIDI-enabled keyboard or synthesizer using a MIDI harp and control MIDI-enabled computer programs with the instrument. Essentially, the harp can produce as many tones as an electronic keyboard when it is equipped with MIDI.
The musical language of MIDI is split into 16 different channels. These channels work like the channels on a two-way radio because the devices have to be set to transmit and receive over the same channel for communication between them to be possible. Users can only communicate with another instrument with a MIDI harp if both instruments are set to operate on the same MIDI channel. If two devices are transmitting MIDI information to one other device, the receiving device will only produce the note information sent down the designated receiving channel.
Different MIDI harps have slightly different features, but there are a few overriding similarities between most types. Generally, a MIDI harp will be portable and comfortable to play, and have features such as a pitch-bend control which allows a note to be raised by half a step. MIDI harps have electronic pickups, either on each individual string or strategically located across the instrument. Most MIDI harps have between 31 and 47 strings.