MIDI 110129.1 Introduction to MIDI
Simply stated, Musical Instrument Digital Interface
(MIDI) is a digital communications language and com-
patible specification that allows multiple hardware and
software electronic instruments, performance control-
lers, computers, and other related devices to communi-
cate with each other over a connected network. MIDI is
used to translate performance- or control-related events
(such as playing a keyboard, selecting a patch number,
varying a modulation wheel, triggering a staged visual
effect, etc.) into equivalent digital messages and then
transmit these messages to other MIDI devices where
they can be used to control sound generators and other
performance parameters. The beauty of MIDI is that its
data can be easily recorded into a hardware device or
software program (known as a sequencer), where it can
be edited and transmitted to electronic instruments or
other devices to create music or control any number of
parameters.
In artistic terms, this digital language is an impor-
tant medium that lets artists express themselves with a
degree of flexibility and control that wasn’t possible at
an individual level beforehand. Through the use of this
performance language, an electronic musician can
create and develop a song or composition in a practical,
flexible, affordable, and fun production environment.
The word interface refers to the actual data commu-
nications link and software/hardware systems in a con-
nected MIDI network. Through MIDI, it’s possible for
all of the electronic instruments and devices within a
network to communicate real-time performance and
control-related MIDI data messages throughout a
system to multiple instruments and devices via MIDI,
USB, or FireWire networked data lines. Given that
MIDI data can simultaneously transmit performance
and control messages over multiple channels (usually in
groupings of 16 channels per port), an electronic musi-
cian can record, overdub, mix, and play back their per-
formances in a building-block fashion that resembles
the multitrack recording process. In fact, the true power
of MIDI lies in its ability to edit, control, alter and auto-
mate parts of a composition after the original perfor-
mance has been recorded, allowing performance
parameters to be easily altered in ways that are unique
to the medium.
29.1.1 What MIDI Isn’t
For starters, let’s dispel one of MIDI’s greatest myths:
MIDI doesn’t communicate audio it cannot create
sounds! It is a digital language protocol that can only be
used to trigger and/or control a device (which, in turn
generates, reproduces, or controls the sound). Thus, the
MIDI data and the audio routing paths are kept entirely
separate from each another, Fig. 29-1. Even if they digi-
tally share the same transmission cable (such as through
USB or FireWire), the actual data paths and formats are
distinct.
In short, MIDI’s control-related language can be
thought of as the dots on a player-piano roll—when we
put the paper roll up to our ears, we hear nothing. How-
ever, when the cutout dots pass over the sensors on a
player piano, the instrument itself begins to make beau-
tiful music. The analogy is pretty much the same with
MIDI. A MIDI file or data stream is simply a set of
instructions that pass through wires in a serial fashion,
but when an electronic instrument interprets the data,
we then hear sound.
As a performance-based control language, MIDI
complements modern music production, by allowing a
performance track to be edited, layered, altered, spin-
dled, mutilated, and improved with relative ease under
completely automated computer control and after the
fact, during post-production. If you played a bad note,
fix it. If you want to change the key or tempo of a piece,
change it. If you want to change the expressive volume
of a phrase in a song, just do it! Even its sonic character
(timbre) can be changed! These capabilities merely hint
at the power of this medium that widely affects the
project studio, professional studio, audio or visual and
film, live performance, multimedia, and even your cell
phone!29.2 The MIDI MessageFrom its inception in the early 80s, the MIDI 1.0 spec
(which is still the adopted version to this day) must be
strictly adhered to by those who design and manufacture
MIDI-equipped instruments and devices. As such, users
needn’t worry about whether the MIDI Out of one
device will be understood by the MIDI In of a device
that’s made by another manufacturer (at least the basic
performance level). We need only consider the
day-to-day dealings that go hand-in-hand with using
electronic instruments, without having to be concerned
with data compatibility between devices.
MIDI messages are communicated through a
standard MIDI line in a serial fashion at a speed of
31,250 bits/s. These messages are made up of groups of
8-bit words (known as bytes), which are used to convey
instructions to one or all MIDI devices within a system.
Only two types of bytes are defined by the MIDI speci-
fication: the status byte and the data byte.