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MIDI Basics: What is MIDI?

It will soon be on over two billion devices, but what is it, and what can it do for you?

by Phil O'Keefe

Even if you're new to the world of modern musical devices, you've probably noticed the word MIDI. It might not be everywhere, but by the end of the year it will be on at least two and a half billion devices, thanks to the addition of MIDI to Android devices and web browsers like Chrome. But what exactly is MIDI, and why should you care? Where did MIDI come from and what does it have to offer you? Let's find out in this first of a series of articles covering MIDI basics.


So What Is MIDI?

For a more in-depth overview of the history of MIDI and the people behind it, check out Craig Anderton's article "A Brief History Of MIDI," right here on Harmony Central. MIDI, which is short for Musical Instrument Digital Interface, is a communications and hardware protocol that was developed in the early 1980s in an unprecedented cooperative effort on the part of multiple companies. At the time, synths, drum machines, sequencers and computers from different manufacturers didn't always communicate well with products from other companies. The original idea behind MIDI was to develop a non-proprietary universal connection and communication system that would work with gear from any company that implemented it, and would allow functionality like connecting two synths from different companies together and play them both simultaneously from either keyboard.

What MIDI Isn't

MIDI isn't audio or something you hear, it's data that represents performance data. A good analogy is a computer keyboard. When you type a letter, it sends a code (defined by the ASCII protocol that associates particular codes with different characters) to the computer, which recognizes that code as a letter and displays it on your screen. Similarly, if you press a key on a keyboard, it sends a code (as defined by the MIDI specification) to a tone generator, which recognizes the code as a note and plays it. However MIDI doesn't just transmit info about notes, but also the dynamics with which you hit a key, volume levels based on footpedal position, and more - much more.


Over the years, MIDI has been expanded so that it controls lighting (as used by many Broadway shows), can play ring tones on your phone, control pyrotechnics at your favorite rock band's concert, and some companies even use it for home security control. But returning to musical instruments, compared to audio MIDI creates very compact data streams and file sizes - which is ideal for mobile devices and the web. For example, a MIDI message that says "a C note was play at a certain time with a certain amount of dynamics, and release a certain amount of time later" would take only a few bytes to transmit.


MIDI accommodates controller data, not just notes - for example, if you move the modulation or pitch wheels on a keyboard to further shape the sound, that information becomes part of the MIDI data stream. It can then control other connected devices, or even be recorded for later playback. In that sense, MIDI acts like a high-tech player piano - but instead of playing piano keys based on holes in a piece of paper, it plays notes based on data embedded in a data stream.


MIDI can also send and receive tempo and synchronization information, and includes MIDI Program Change commands that can change an instrument's basic sound (for example, from piano to rock guitar). There's even a part of the MIDI spec called General MIDI, which specifies a general sound set of 128 sounds assigned to specific "program numbers." Sending the appropriate program number to a device will call up a specific sound. 


MIDI is also great for composers and arrangers, because you connect your keyboard (or other MIDI controller, like a MIDI-compatible guitar or drum set) to your computer and record complex arrangements for later playback or for printing out lead sheets and notation. Furthermore, MIDI isn't limited to controllers - devices such as effects units can respond to MIDI as well. And, not all MIDI is hardware-based - software-based virtual MIDI instruments that run on your computer, tablet or even your smartphone have become very popular. 


Tune In To The Right Channel

How the device responds to the incoming MIDI data depends on its features and capabilities, and how it's designed - not all devices transmit or respond to all MIDI messages, and it's often possible to tell a device to ignore particular types of messages. In addition, there are 16 MIDI channels so you can send unique data to 16 different MIDI receivers at once. Just as your cable TV coax cable carries multiple channels and allows you to watch one program in one room while other people are watching different things on TVs in other parts of the house, MIDI lets you send a different information to different devices that are set to "listen to" different channels. You might have a MIDI piano part on Channel 1, a funky bass part on Channel 2, and a cool beat on Channel 10, with all that data traveling down a single MIDI cable. So, do you need separate devices for all those different parts? Not necessarily - some devices are multitimbral and can respond to multiple MIDI channels at once, with each part set to create a different sound.  

Originally, MIDI was designed as a hardware interface, with 5-pin DIN cables used for the connectors and are three kinds of MIDI ports - In, Out and Thru. Outputs connect to inputs, and Thru ports replicate what's being received at the device's MIDI In jack, allowing multiple devices to be connected in a daisy chain. While the original MIDI connectors are still used on many new products today, you're just as likely to find devices that transmit and receive MIDI over a USB connector or even wirelessly over Bluetooth.

What Else Is It Good For?

Many other functions are possible with MIDI, such as recording (or "sequencing") MIDI data. Once recorded, MIDI data can be manipulated in all sorts of ways that are not possible with audio. For example, while you may have been listening to a piano patch on your keyboard when you recorded the MIDI data into your MIDI recorder, it's possible to play it back on a keyboard that has a harpsichord sound loaded. This makes it very easy to try out different arrangement ideas without committing to a specific "sound" as you'd have to if you had recorded audio. You can also record tricky-to-play material at a slow tempo, and then play it back at a faster speed without affecting the pitch - unless you want to; transposing a performance after the fact to a different key is also easy to do with MIDI.  Did you play a wrong note? The MIDI editing features found in most DAW and sequencing programs allow the pitch and even the timing of notes to be adjusted easily.


Web MIDI opens up even more possibilities, like being able to play instruments remotely, take lessons, streaming MIDI data from the web to a tone generator for karaoke, collaboration, and music playback that requires virtually no bandwidth - so even if you have a horrible internet connection on a mountaintop, you'll still be able to play music.


Besides layering keyboards for a fatter sound, creating virtual MIDI tracks for bigger, more complex arrangements and productions that put less stress on your computer than audio tracks, and making it possible to control complex systems consisting of multiple effects and synthesizers on stage and in the studio, MIDI can do much more. In future articles we'll look into some of these options, as well as some of the deeper details and benefits of MIDI, in the months to come -stay tuned!

For more information on MIDI, visit The MIDI Association web site.




Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.  

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sunsetb  |  March 28, 2016 at 8:56 pm
I have never come across any expert (or otherwise), who could explain (to the average musician), how to use Midi in a straight forward and sensible way (with good examples of typical setups), and I've been looking at Midi in and out for years (no pun intended). Here's the chance for you to do it properly. Musicians everywhere will thank you if you do a good job.
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