What is MIDI

by Anders Johanson August 29, 2020 6 min read

ROLI MIDI Controller

MIDI is short for Musical Instrument Digital Interface and it is a standardized audio interface. It is used to connect a computer's MIDI input/output devices (keyboard, microphone, or mouse) to other hardware, often a musical instrument. Technically, MIDI is the file format of which standard MIDI-capable hardware is capable. Since the mid-1970s, many computers have incorporated one or more MIDI-compatible MIDI controller ports, which allowed musicians to control those devices (up to a MIDI keyboard and a MIDI drum machine) in real-time, using their MIDI-capable synthesizer, sequencer, sampler, etc.

A musical instrument takes an input MIDI input signal, which can be as simple as an audio signal, and produces a MIDI output signal. MIDI-capable devices can send/receive data in several ways. A MIDI compatible instrument like the Roland FT-817 produces a MIDI note and plays it on its own devices or can copy it and play it on another instrument. An example of a device that creates a MIDI note is an octave piano. The notes are produced when a key is pressed, or a gate button is pushed, sending the resulting electrical signal to an amplifier to generate a pitch that is the audio amplitude of the note.

How MIDI Works

MIDI can create most common musical notation signals including triads, fifths, and octaves. Although MIDI is a native technology for controlling sound synthesizer, it is not well-suited for conventional acoustic instruments, as it does not support timbre and varies the pitch of the instrument for arbitrary intervals. MIDI also has considerable digital and analogue manipulation capabilities for the creation of and modification of sounds. While devices typically do not produce an audio signal, any MIDI input can be combined with other MIDI sources to produce sound. For example, the MIDI input from a digital audio workstation can be combined with MIDI input from an audio tape machine, or the input from an audio mixing console, to form a signal that generates a noise or other new sound. 

What does MIDI do?

MIDI is an invention of the 80s that has come a long way since. It stands for musical instrument digital interface. It is basically a score that is read by a compatible music synthesizer. If you play a note on your keyboard, the MIDI converts it into numbers and sends it to the software or hardware that will then make that sound

If you change the score, the sound changes. It is the music equivalent of a word document. These days, MIDI is rarely used to play music. Most music is either recorded in a professional studio or performed live. However, MIDI is still used for music creation. It's a great tool for composition since it takes some of the tedium out of writing notes and playing them back to hear how they sound. MIDI's main use nowadays is in gaming.

Many video games use MIDI files for music rather than recorded music because the size of the files is so small. It takes up a lot less room on the console or could allow for more songs to be stored in memory. You can also purchase and download songs online in MIDI format. This is a popular way for amateur and independent musicians to distribute their music. It cuts out the record company and makes it easier for people to get the music to the audience. Instruments that can play MIDI are relatively inexpensive and easy to find. They are the closest thing to a "music cartridge" as far as equipment goes. You can find MIDI keyboards for under a $100 nowadays. The downside of MIDI is that it is fairly restrictive to the notes that can be played and takes some of the human element out of creating music.

There are several different types of MIDI files. The most common ones are: Song files: Just what it says. These files contain the notes to a particular song in MIDI format. These can range from simple songs to play on a piano to complex orchestral pieces. Instrument files: These contain instructions on how to play a particular instrument.

How does MIDI work?

MIDI is a standard for talking to electronic music hardware. There are several variants of MIDI, but they all translate musical notation, written or generated in the electronic or computer-generated field, into a series of electrical signals that can be played back and recorded on hardware. The MIDI specification uses 2.5mm sockets, so most keyboards sold today will be compatible with it. The (for now) recent fashion for electronic keyboards doesn't affect the compatibility. A MIDI switch on a keyboard determines whether it is compatible with MIDI. A non-MIDI keyboard with a MIDI switch in the power-on state will cause the machine to refuse to operate if the switch is touched again, even if the keyboard itself is not powered on.

MIDI Setup

Is MIDI Analog or Digital?

MIDI is an interesting creature in that it isn't entirely analog or digital. It falls somewhere in between. MIDI contains three different types of data:

  1. Note On/Off
  2. Continuous controllers (controllers that send a signal such as the volume or modulation wheel)
  3. System messages (these are data that communicate with the MID) That first type of data, note on and note off, will be converted into a signal that a MIDI device can understand. For example, a MIDI device may see a certain note on signal as the number 40. That means that on key number 40 (middle C) was pressed on the keyboard.

There are 128 possible notes that can be played on a keyboard. Numbers 0-127 refer to different keys on a keyboard. MIDI takes those numbers and converts them into a series of on's and off's. For example, the number 40 converted to binary would look like this: 1000000000000 This just means that on key number 40 was pressed. The 1's are on and the 0's are off. When the key is released the 1's turn off and the 0's turn on. This type of data is very compact and requires very little space on a hard drive. The other types of data don't get converted into a numerical code. They are more like instructions to a MIDI device. For example, the data may tell a MIDI device that the there is a volume change or a modulation to happen.

Should I get a midi controller or a synth?

If you’re asking questions like “Should I get a midi controller or a synth?” then I think a midi controller (MS-20-style) is more suitable. In that case you’ll be able to trigger chords and sequences using the controls, which is the main thing you want to be able to do. In that case the money spent will be well justified by what you can do with it. The full kit looks pretty comprehensive, and I’m sure you could even get a semi-modular synth along with it if you wanted to:

What would be a good starting point for someone interested in such a rig? There’s a range of synths around the £100 mark which would be a good starting point for someone who’s only just started out. The most affordable is the Midi Fighter Controller (£150). I think that the Midi Fighter Controller has really nice sound qualities and isn’t bad for its price. 

MIDI Controller

Can I use my keyboard as a MIDI

No. You cannot change your keyboard into a MIDI-compatible device. You can load and save keyboard patterns and you can use them on any application or hardware, but you can't use a device in the firmware to program the hardware.

To create a "MIDI controller", we need to hook up the functionality of the keyboard to a "MIDI" device, to communicate to it the specific keys that the software needs to control. For example, a keyboard is a MIDI controller that has the ability to change the pitch of notes. We can hook up this pitch change functionality of the keyboard to the software, and the software will then be able to control the pitch and control the notes that are played.


I own a keyboard that is MIDI-compatible but not MIDI-compatible. Can I still use it?

Yes. In fact, it can be used directly with any other MIDI-compatible equipment you can find. You can usually connect it to a controller, but in some cases you may have to use a patch cable instead (more on patch cables below). Warning: Some musical equipment, particularly guitars, will not accept MIDI at all, so a MIDI compatible keyboard may be required in order to play the keyboards on that equipment. 

    Anders Johanson
    Anders Johanson

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