Magazine article American Harp Journal

The MIDI Harp: What Is a MIDI Harp?

Magazine article American Harp Journal

The MIDI Harp: What Is a MIDI Harp?

Article excerpt

MIDI is an acronym that stands for Musical Instrument Digital Interface. It is the way electronic musical instruments communicate, pass data back and forth, one to another. This protocol of messages and the hardware for passing them was standardized in 1983 at a meeting of the major manufacturers of electronic instruments. It has been universally implemented across the industry, so that any electronic unit designated as MIDI can be plugged into any other MIDI unit, and they will work together.

Central to all electronic music is a synthesizer of some sort. A synthesizer can be a chip in your keyboard instrument, a rack mounted appliance, or software in your computer. Synthesizers respond to messages coming from a MIDI controller and create sounds according to the parameters of these messages. The controller can be a piano style keyboard, a guitar, a set of drums, or even a harp.

The messages are digital. Digital information is a code of on-off pulses that can be understood only if you know how it was encoded, and have the capability (hardware and software) to decode it. Digital information, in its encoded form, is a description of a physical event. The more detailed the description is (in sample size and frequency), the more complete the realization will be of the original event.

Analog information, on the other hand, is a physical representation of a physical event. For example, a phonograph record has variations in the vinyl disc groove that are analogous to the variations in the sound waves that were recorded. When you play the recording, the phonograph needle is wiggled in a way that is analogous to the original sound waves, and an electrical current is produced that, once again, fluctuates in a way that is analogous to the original sound. This current causes the loudspeaker cone to move in this same manner, and sound is produced that mimics the original.

Sound that has been recorded digitally has been converted from the analog domain to the digital domain. In order to hear this sound it must be converted back to the analog. Why do we go to this trouble? It's because analog recordings suffer losses in each transmission, and over time the medium it is recorded on degrades, with further information loss. A digital description, on the other hand, stays exactly the same, once formulated. It can be duplicated and transmitted an infinite number of times with no loss of information.


The MIDI Harp

The MIDI harp, or any electric harp for that matter, has a piezo transducer touching each string. Piezo material has the magical property of emitting an electric current whenever stressed by bending or compression of some sort. In this case, the vibration of the plucked string causes the piezo pickup to output a current that is analogous to the vibration. If this were an ordinary electric harp, we would simply stay in the analog domain, and route this current to an amplifier which drives loudspeakers to deliver your music to the audience.

But the MIDI harp has a microprocessor, sort of a miniature computer that converts the analog signal to digital information. Based on the parameters of this digital information, a MIDI message is formulated and sent via the MIDI-out port. This MIDI message describes your string pluck: how loud it was, how long it lasted, and so forth. What a MIDI message does not describe is the actual sound that you would have heard had you been sitting in front of the harp. Sound must be supplied by the synthesizer that your harp is controlling.

Synthesizers use several different methods to produce analog sounds, and the recipe for making each particular sound is stored in memory as a file or "patch." If you want to hear a certain variation of piano sound, for example, you select that patch, and any note-on messages coming to the synthesizer will be implemented with that sound. Today's synthesizers use sophisticated techniques to produce very lifelike sounds, although for creative purposes a tone that sounds "synthesized" may be exactly what is needed. …

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