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MIDI:

Musical Instrument Digital

Interface

By BOB MOOG

MIDI (Musical Instrument Digital studios, MIDI is enabling traditional Terms that havcTa specific, unique

Interface) is the specification for a and amateur musicians to produce meaning in MIDI are shown in italics

set of digital codes for transmitting high-quality music with modestly and are defined when they are first

music control and timing information priced, readily available equipment, used in the text.

! I

in real time, and for the hardware And, in academic laboratories and W_AT iS MIDI?

interface through which the codes are computer music facilities around the

transmitted, world, MIDI is providingan inex- I,,,, .....

Basic ideas for a digital musical pensive link between large research MIDI 1.0 DETAILED SPECIFI-

instrument interconnection standard computers and conveniently pro- CATION is the document that cur-

(then called Universal Synthesizer grammable, musician-oriented tone- rently defines the Musical Instrument

Interface) were proposed by Dave producing instruments. Digital Interface. The bulk of the

Smith and Chet Wood at the 70th The meteoric (and largely unan- specification describes the numerical

Convention of the Audio Engineering ticipated) rise in the popularity of codes that represent the various types

Society in November 1981. By the MIDI, and in its importance to con- of musical information that can be

end of 1982, the name had been temporary musicians, has created a transmitted via MIDI. A description

changed to Musical Instrument Dig- blizzard of confusion and miscon- of the hardware that transmits and

ital Interface, and several electronic ception among its users. Like all receives the MIDI signals occupies

musical instrument manufacturers system specifications, MIDI was only two pages of the specification.

had agreed on a comprehensive tech- drawn up with certain goals, starting We will now describe the hardware

nical specification. The first docu- assumptions, and compromises in interface and mention some MIDI

mented MiDI hookup between in- mind. Some of its limitations are easy operating characteristics that are at-

struments of two different manufac- to assess; others are still the subjects tributable to its hardware design.

turers took place, without formality of discussion and disagreement, even

or ceremony, at the National Asso- among MIDI aficionados.

ciation of Music Merchants conven- The purposes of this article are a)

tion in January of 1983. to explain what the MIDI specifica~

In the three or so years since MIDI tion is at the present time, and b) to The MIDI hardware interface is a)

first saw the light of day as a func- review its applications--especially digital, b) serial, and, to a limited

tioning technical specification, mil- with respect to the operating char- extent, c) bidirectional. A digital in-

lions of MIDI-equipped instruments acteristics of currently available terface transmits information as a

have been made and sold, and count- equipment and software. We assume stream of numbers. MIDI numbers

less thousands of music producers that the reader is familiar with syn- are eight bits long, which means that

have embraced its capabilities. On- thesizers and basic audio studio each number specifies one of 256

stage, electronic instrument per- techniques, and wants to use MIDI possible values. A serial interface

formers use MIDI to network their to get the most from his equipment, transmits numbers one bit at a time--

synthesizers, sequencers, and rhythm Discussionsofthe merits of the MIDI a data transmission format that re-

machines. In the studio, personal specification itself, or of the advis- quires only a simple, two-wire cable.

computers equipped with sophisti- ability of implementing alternate, A bidirectional interface is capable

cated MIDI-based software are higher performance interconnection of transmitting information in both

transforming the way music is corn- standards, are primarily of academic directions. Because MIDI informa-

posed electronically. In thousands of interest, and are not included in this tion flows entirely as a stream of

churches, living rooms, and garage article, numbers that must be formatted in

394 J. Audio Eng. Soc., Vol. 34, No. 5, 1986 May