MIDI is the acronym for Musical Instrument Digital Interface. It is actually a protocol for “translating” the parameters of acoustic music into a format that computers and music hardware can comprehend. While musicians could refer to a piano playing a quarter note middle C at mezzo-forte, computer software would need to understand this as a series of numbers. MIDI takes acoustic aspects of music and converts them into a numeric “standard”. For example, a piano timbre = 1, a middle C is 60, mezzoforte a 64.

MIDI was introduced in 1983. It was developed in cooperation between the major music industry electronic instrument manufacturers including Roland, Yamaha, Korg and others. The MIDI protocol allows electronic devices (usually synthesizers, but also computers, light show controllers, multi-track recorders, etc.) to interact and work in synchronization with other MIDI compatible devices. Using a master controller device such as a keyboard, one can play or trigger sounds from other electronic devices remotely. The characteristics are as follows:

1. Duration = time of NOTE OFF – time of NOTE ON (if NOTE ON @ 0.00 and NOTE OFF @ 1.00, duration was one second)
2. Timbre = PATCH [1 to 128]
3. Pitch = MIDI Note Number [1 to 128] C-2 to G8
4. Part or Staff = CHANNEL – MIDI “broadcasts” using 16 channels, with Channel 10 = drums.
5. MIDI also has “running status” meaning anything stays until it changes (if you tell a midi keyboard part to use the “Vibraphone” patch, it stays vibes until a different patch is sent.)
6. MIDI is NOT audio – the “sound” comes from a MIDI device of some kind (including the computer’s sound card).

A MIDI file doesn’t contain actual audio data, but rather contains commands that let MIDI-capable synthesizers re-create a specific musical passage. The MIDI protocol has been used for years as a way for electronic musical instruments (like digital keyboards and sequencers) to communicate with each other.

An important distinction of MIDI files is that they have NO inherent sound – they require an external device or an internal “sound font” for any music to be heard. This is similar to a piece of sheet music – the page contains music notation which on their own have no sound. A musician is required to ‘convert’ the music notation to actual audio sound.

Computers typically feature the ability to interpret MIDI files into music, built into the operating system. Since they don’t actually contain the music itself, but rather the commands used to re-create music, MIDI files are a lot smaller than audio files like MP3s, WMAs, or WAVs. MIDI files usually appear with the “.MID” filename extension.

The idea of a sound font parallels that of a word processing font – the font is able to represent a particular instrumental or vocal sound – a ‘timbre’. One aspect of MIDI is the idea of ‘patches’ – any device that fully supports General MIDI is based on a standard listing of 128 sounds (patches).

General MIDI (GM) Drum Sounds

Assigned to each MIDI note (channel 10) – NOTE: 36 = C1 [middle C = C3]

Excerpts from http://www.midi.org/aboutmidi/intromidi.pdf

Electronic musical instruments offer an incredible array of sounds to professional and amateur musicians. They place at a musician’s fingertips everything from traditional, real-world sounds to noises that have never been heard before.

They come in all shapes and sizes, too, from solid, physical instruments such as keyboards, beat boxes, and electronic drum kits, to computer-based “virtual” instruments, or “soft synths.”

All of these devices rely on something called “MIDI.” You really can’t get too far with an electronic instrument without bumping into MIDI. This is actually a good thing, though, since MIDI allows you to do all sorts of exciting musical things.

Of course, it helps to know what MIDI is—that’s what this booklet’s for. Once you understand the basics, you can consult the documentation for your device to learn more about how it uses MIDI.

Understanding MIDI

What MIDI Isn’t

Yes, it’s an odd place to start, but one of the things that confuses people new to MIDI is that they assume MIDI is some type of sound, or audio, that travels through MIDI cables. It’s not.

What MIDI Is

MIDI, which stands for “Musical Instrument Digital Interface,” is a system that allows electronic musical instruments and computers to send instructions to each other. It sounds simple, but MIDI provides some profound creative opportunities.

Why MIDI Matters

Here are just some of the things MIDI makes possible:

• You can use a MIDI instrument with which you’re comfortable to play the sounds belonging to any other MIDI device, including soft synths.
• Create rich musical textures by layering sounds from multiple MIDI devices, or assign different sounds to play in different pitch ranges.
• When you play a MIDI instrument, it produces data that can be captured by a MIDI “sequencer.” When the sequencer plays back the data, your original performance is recreated. Sequencers aren’t just MIDI recorders, though—they let you fix mistakes, change the pitches of your notes, fix their timing, the way they play, the sounds they use, and more. In addition, most sequencers can capture multiple performances on separate“tracks,” allowing you to build up full musical arrangements, one track at a time.
• The General MIDI sound set allows you to instantly play back pre- recorded music on many MIDI instruments, or on a computer.
• One MIDI device can control another, letting you use the most convenient tool for any job. Edit MIDI instrument sounds on your computer, operate an audio recorder from a MIDI beat box, and on and on.

What MIDI Does

When one MIDI device communicates with another, it’s all about instructions: It’s just one MIDI device telling another one what to do. Here’s how playing a note—the most common MIDI activity—happens.

Suppose you’ve got a MIDI keyboard connected to a laptop via a MIDI interface and you want to play a Middle C…

When you hold down the Middle C on the keyboard, the keyboard sends out a Middle C “key down” MIDI message to the laptop. The laptop says to itself, “Ah, right, Middle C,” and receives a “note on – Middle C”

When you let go of Middle C, the keyboard sends a Middle C “note off” message to the laptop, and the note stops playing.

Note-on and note-off messages are just the beginning, though. Most MIDI controllers can also sense how hard you play a note, transmitting a MIDI “velocity” value to the receiving device so the volume or brightness of its note responds to your touch.

And, of course, you’ll usually play more than one note at a time.

We’ll discuss other types of MIDI messages a bit later, and explain how they’re put together.

A World of MIDI Controllers

A MIDI device that controls another is referred to as a MIDI “controller.” Though most people think of MIDI as being just for keyboard players, a wide range of MIDI controllers and control surfaces make it easy for all sorts of players and engineers to harness the power of MIDI.

Let’s talk about some of the available controllers just to give you some idea of the possibilities.

Keyboard Controllers

This is the most popular type of controller due to its familiarity (mimics a piano) and ease of use in a variety of scenarios. Keyboards can be divided into several categories:

1. controllers – ONLY provides MIDI output and thus requires some kind of digital device to actually create sound. This is similar to a bluetooth QWERTY keyboard – without a computer, such a keyboard is fairly useless! One quick way to tell that a device is a keyboard controller is the lack of either speakers or headphone jack (nothing in the device can actually generate sound)
2. synthesizers – these are instruments that have a ‘tone generator’ in them, as well as audio output (headphone jacks, line out, and/or speakers). Synthesizers are fully functional MIDI controllers BUT they have the added benefit of being able to produce hundreds, and sometimes thousands, of sounds (timbres)
3. digital keyboard – these are instruments that have the sense of ‘weight’ in the piano keys in order to provide a feel of playing more like a piano. Digital keyboards tends to have fewer timbres since they are trying to mimic, as close as possible, an acoustic piano.

Guitar Controllers

A steel-stringed guitar with a MIDI pickup or a dedicated MIDI guitar synthesizer can allow the performer to not only create MIDI content, but use standard guitar techniques to make that content as expressive as possible.

Drum Controllers

Electronic drum sets offer a totally natural playing experience along with incredible sounds, all without the hassles of a traditional kit. You can practice on headphones all night if you want, or record drum tracks straight into a MIDI sequencer from a drum kit’s pad and cymbal controllers. There are smaller drum controllers you can play with sticks, or even with your hands. You can also control MIDI devices from traditional acoustic drums by installing MIDI drum triggers.

Other Controllers

There are a number of other instruments and devices that use MIDI. There are specially made MIDI wind controllers, mallet controllers, and even MIDI accordions. Since MIDI was primarily designed for keyboard players, these devices are often referred to as “alternate controllers”.

Another category of alternate MIDI controllers are those that don’t mirror traditional musical instruments. These are simple switches and controls that can be used in items as various as clothing (gloves, suites, mats), to objects that can be hit, strummed, blown, or even controlled by a light beam.

MIDI devices can not only be used to trigger note information, but they can also send control information to other devices, such as lighting controllers.

The Power of MIDI Sequencers

A MIDI sequencer can provide a tremendous amount of fun for the amateur musician, and it’s a powerful tool in the hands of a professional. In fact, sequencers play an important role in many modern commercial recordings.

During recording, the sequencer captures and plays back live MIDI performances. Performances can also be constructed slowly, note-by-note using a variety of methods include “step record” and onscreen pencil tools that allows the ‘drawing’ of notes.

A sequencer may let you view notes in an variety of ways, from a list of MIDI events, to a piano-roll-type view, to onscreen notation. (Many sequencers also allow you to print the notation you see onscreen.)

The capturing of MIDI notes is just the beginning, since a sequencer allows you to do all sorts of things to perfect your music. Some of the most commonly used sequencer tools are:

• quantization—that corrects the timing of notes.
• transposition—that moves notes to new musical keys.
• scaling—that changes the feel of recorded musical phrases by adjusting recorded velocity values, note lengths, and more.

Some instruments contain a built-in sequencer, giving you sounds and sequencing in a single “workstation.” There are also numerous computer- based sequencing programs and standalone hardware sequencers.

Some sequencers can record audio in addition to MIDI, allowing you to work on all of the elements in a song at the same time.

Standard MIDI Files, or “SMFs”

Whether a sequencer’s in a workstation, on a computer, or a standalone device, each song’s data has to be stored as a file somewhere, somehow. Each manufacturer has their own type of sequencer file that works for their products’ features, resulting in files that only their sequencers can play. This presents a roadblock for musicians who want to collaborate or otherwise share sequencer files.

The solution is the Standard MIDI File, or “SMF,” format. This standardized sequence file format allows music to travel from one sequencer to another, since most modern sequencers can play SMFs, and store songs as SMFs. An SMF may not contain all of the bells and whistles that make any one sequencer unique, but it supports the features that are common to all sequencers, and this makes them extremely handy.

Two Types of SMFs

SMFs come in two flavors:

• Type 0 SMFs—contain a single sequencer track that holds recorded performances for up to 16 different sounds.
• Type 1 SMFs—can contain multiple sequencer tracks.

MIDI and Video

MIDI doesn’t have to be simply about music. Some MIDI devices allow performers—called “VJs”—to manipulate video images onstage, creating exciting visuals. Special software on a laptop computer along with DJ-style physical controls open up a world of video possibilities, letting VJs remotely select clips and control how they behave.

Also, some keyboards have a button that, when pressed, instantly reconfigures the keyboard’s knobs, sliders, and buttons as controllers for an attached video playback system.

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