A Beginner’s Guide To MIDI: What Is It? How Does It Work?

MIDI is a word you will see thrown around a lot when reading about recording music at home. As a beginner, I owned and used a lot of MIDI equipment without really having a clue how it even worked.

In this guide, I will share with you (in simple terms) what I have learned, to help you begin to understand the world of MIDI.


What does MIDI stand for?


MIDI stands for Musical Instrument Digital Interface.


 A Brief history of MIDI


MIDI was invented in 1983. As there was no standardized means of synchronizing electronic musical instruments from different companies together.

Trying to get two instruments to communicate was a little like getting an English and a Japanese speaker in a room and asking them to converse when neither knows any of the other person’s native language.

This function was quite essential when creating music with more than one instrument. After all, you don’t want to be limited to just one companies products (he says typing this on an Apple laptop).

A meeting between Roland founder Ikutaro Kakehashi, Oberheim Electronics founder Tom Oberheim and Sequential Circuits president Dave Smith in the early 1980s started the discussion with representatives from Yamaha, Korg and Kawai that a universal language should be created so that various instruments could communicate with one another.

The idea of this musical ‘standard’ was proposed at the Audio Engineering show in November 1981.

Eventually, this lead to Robert Moog announcing MIDI in October 1982 and it was demonstrated for the first time in 1983 with signals being transmitted between a Sequential Circuits Prophet 600 and a Roland JP-6. (Both are still awesome synths by the way, check out the video below for a glimpse at the Prophet).




How does MIDI work?


No audio signals (sounds) are sent via MIDI. Instead MIDI works as a digital signal. A series of binary digits (0s and 1s).

Each instrument (or computer) understands and then responds to these 1s and 0s, which are combined into 8-bit messages supporting data rates of up to 31,250 bits per second.

These messages can communicate useful information such as:

  • which note is pressed
  • the moment a note is pressed and released
  • the velocity (how hard it is pressed)
  • after-touch (when key pressure changes)
  • vibrato, and even;
  • pitch bend,

The MIDI ‘protocol’, as it is known, can support up to 128 notes, ranging from C five octaves below middle C up to G ten octaves higher. So pretty much any note you could ever wish to play.

Other values such as velocity are recorded as numbers between 0 and 127. With a 0 being no sound and 127 being the loudest.

These standardized numbers can be read by any instrument or machine capable of understanding MIDI. Which is why MIDI is such a powerful tool in music production.

This type of MIDI mentioned above is known as ‘general MIDI’ but it is worth bearing in mind the capability varies depending on the age of the instrument you are using.

  • GM Level 1 – developed in 1991 and consists of a minimum of 128 patches, 24 notes of polyphony,16 channels and 16 part multitimbrality
  • GM level 2 – implemented in 1999 includes more sounds and features. 32 notes of polyphony and 16 simultaneous instrument sound patches, reverb and chorus effects were also added.

To show it is a digital and not an audio signal, it can actually be used for many other functions as well as for music. MIDI has been used to trigger light shows in theatre productions for example. It can basically be used to control any digital device that can read and process it.


How is MIDI data transferred?


MIDI is quite an old-school kind of connection and pre-dates USB. So if you have only recently got into music production, then traditional MIDI may take you longer to get your head around.

Traditional MIDI is one directional. A MIDI device is therefore equipped with ports for ‘MIDI in’, ‘MIDI out’ and ‘MIDI Thru’. A special type of cable known as a MIDI cable (no surprises there) is used to make these connections. Each wire is actually made of 3 wires, two are used for data transmission and one is a shield.


Image: Pretzelpaws CC-BY-SA-3.0, via Wikimedia Commons


Each MIDI connection along one of these cables (or ‘link’), can contain up to 16 channels of information and each MIDI device has 16 channels. Each one of these channels will have its own specified note, velocity, pitch bend etc.

It gets slightly confusing as MIDI signals can now be transferred via USB. This is common in most modern synths or MIDI keyboards.  The USB effectively takes the place of the In, Out and Thru ports.


MIDI Clock


On top of these standardized numbers. MIDI also includes something known as a ‘clock’ pulse. This defines tempo and allows you to sync various equipment together.


What is MIDI sequencing?


MIDI sequencing records notes in the system as MIDI rather than immediately converting to audio.

This data is presented usually in something known as a ‘piano roll’. Now before you accuse me of trying to make you eat a keyboard sandwich….it is actually something you find in most Digital Audio Workstation (DAW) programs.


What is a Piano Roll?


This is typical in most pieces of DAW software and is shown below in Ableton Live



As you can see it is sort of like a graph with the y-axis being the pitch (shown on a piano keyboard, hence the name ‘piano roll’) and the x-axis being time.

So in this example, I am playing ‘G’ 3 octaves above middle C for 1 bar, ‘C’ 3 octaves above middle C for 1 bar, then ‘E’ 3 octaves above middle C for 1 bar and finally ‘D’ 3 octaves above middle C for 1 bar.

You can see at the bottom another small graph, this is the velocity of each note between 0 and 127 as I mentioned earlier.



This stored data is then played back on whatever virtual instrument you have loaded onto that particular track. And the beauty is you can change it with a single click. It can go from a piano sound to a flute, even to the sound of a barking dog if you are that way inclined.

Sequencers have many advantages and allow you to craft a track with amazing accuracy. You can ensure a note starts exactly on time and is played for exactly as long as you wish (down to a 32nd of a note for example).

If you played a wrong note when inputting the MIDI, that is also not a problem. Simply drag and drop it where it was meant to go. But with a sequencer you don’t even have to input the notes using a MIDI controller, you can manually enter the notes using your computer mouse simply by clicking on the piano roll wherever you want to add a note.

In Ableton Live, you can switch between a drawing cursor (that looks like a pencil) to add new notes, or to click on existing ones to remove them. Or you can switch to an edit cursor which will allow you to lengthen, shorten or change notes.




Beware though, as too much correction in some instruments just creates really robotic sounding music with no character.

You can even download ‘Groove templates’ which are a rhythm for a MIDI track. Or transpose a track up a few octaves with just the click of a button.

MIDI really does give you a lot of flexibility when it comes to shaping how your music sounds.


What equipment do you need to produce music via MIDI?


Using a Computer


The easiest way to produce sounds using MIDI is to use the MIDI sequencer built into your DAW software.

As I said above, you can manually enter notes into your piano roll using just your mouse cursor within your DAW software and then adjust other settings within that afterward. But doing it this way is a long process and not very intuitive.


How does a MIDI Controller work?


The more common way to input the notes into the MIDI sequencer is to use a MIDI instrument. This could be a MIDI keyboard, a synthesizer with MIDI capabilities or a drum machine (and many other things).

Below is a picture of my Novation Impulse 49. It is only capable of sending or receiving MIDI signals, it can’t play audio signals. So if you tried to plug it into an amplifier or speaker without going through a sound module or virtual instrument in a DAW first, nothing would happen.



In the image, you can just about make out my Novation Bass-station synth on the left. This synth is capable of sending audio signals and so can just be plugged straight into an amp, unlike the MIDI keyboard to it’s right. However, it is also capable of sending MIDI signals as well, via either USB or traditional MIDI cable. This is the case with most modern synthesizers as I explained in this recent article.

When you play a series of notes on one of these instruments it will send MIDI data for the note played (a number between 0 and 127) and a series of other numbers for velocity, pitch bend etc. This information will be sent along a cable via the MIDI out port or the USB depending on what you are using.

If you are using traditional MIDI 5 pin cables you are unlikely to have a MIDI in port in your computer, therefore you must use some sort of interface.

This could either be a MIDI interface which you can plug your MIDI cable into and then this interface will connect to your computer via a USB connection or similar. Or more common and what I would recommend is to connect to a general audio interface such as this one which has inpits for MIDI but also other types of instruments, microphones etc.



If your MIDI keyboard or other device is more modern, it is likely to just use a USB connection and this can be plugged straight into the computer without the need for an interface. As I mentioned above, the USB acts as the MIDI In, Out and Thru combined.

But your computer has now just received a series of numbers, this alone will not produce a sound. To do this you must have some sort of virtual instrument within your DAW to which these numbers will be applied and a sound will be produced.

There are thousands of virtual instruments or ‘VSTs’ that you can download and add to your DAW. Or in many, such as Ableton Live, a huge library of instruments comes pre-loaded into the software.


Other sound generators


A MIDI signal can also be sent to other machines which can interpret these signals and subsequently produce a sound. This could be a synthesizer module or a sound module which comes loaded with sounds.

You could also use a MIDI sampler, where you can record your own sounds and then play them back using MIDI.

All these MIDI instruments come with a MIDI implementation chart, within which are a list of all MIDI commands along with info on whether the device is poly or mono or if it is multitimbral.


What is MIDI automation?


MIDI automation is a great way to add certain changes at different points to a MIDI track whilst it plays. So, for example, say you wanted the level of the track to change during the chorus to make it stand out, or even if you want to change elements of the EQ mid-song.

This is done in many pieces of DAW software by simply making these changes yourself in real time as the track is recording. This will all be recorded alongside the MIDI track and you will have this automation built into your song.

As with other elements of MIDI you can of course manually add automation after the recording is made or tweak certain elements.

Below is an example of someone playing around with MIDI automation in Ableton Live.


What are the different MIDI modes?


MIDI instruments will often have different modes. This involves turning something known as Omni on or off and then changing between polyphony and monophony.


1) Omni On/ Poly


In this mode, the instrument responds to all MIDI messages it receives. It will then attempt to play all the parts of all instruments attached to MIDI controller. These notes can be played simultaneously as it is set to polyphony.


2) Omni On/ Mono


In this mode, the instrument receives data from all channels but can only play monophonically.


3) Omni Off/ Poly


Polyphonic, but responds only to signals on channels it is set to receive.


4) Omni Off/ Mono


Receives data on one channel and can only play monophonically. This has an advantage if you want to record the sound of an instrument that can’t do chords in real life.


Advantages and Disadvantages of MIDI


MIDI is very popular in music production, in particular in the home recording studio. This is due to several advantages, but there are also some disadvantages you should be aware of too.



1) Size


MIDI files are tiny in comparison to audio files when stored on a computer.

This is because they are stored as a series of simple numbers rather than a complex audio file (MP3 or WAV). This may not be an issue for your storage space if you have a computer or laptop with ample memory. But with smaller files, you cut down the amount of work your system has to do too and when you have complex tracks this will make everything run much smoother.

This is also an advantage if you are collaborating with fellow musician’s. If you want to send files to one another, it will be much quicker using MIDI as opposed to sending lots of huge audio files. Bear in mind though they must have the same virtual instrument in their DAW software to be able to hear what you can.

2) Editability


As I mentioned earlier, as your MIDI tracks are just stored in your DAW as a series of numbers you can edit these numbers to your heart’s content even after you have input your data.

Do you want the piano to build in volume throughout the chord progression? No problem, just alter the velocity values. Did you accidentally hit a G# instead of a G on the very last note of a 5-minute synth piece? No problem, just change the note in the piano roll.

If you record in pure audio you can change these things using transposing or volume alteration, but it is not as easy or quick to do and you will never have quite as much accuracy in altering very specific elements as you do with MIDI.


3) Budget


Possibly the most important advantage for us home musicians is to open up a world of musical opportunities on a budget.

Not many of us can get together a string quartet or even a full live drum kit. By using MIDI, we can take virtual instruments and create complete tracks on a budget. There is now nothing stopping you recording an entire symphony using a full orchestra of sounds, without leaving your bedroom.

I mean, I’m sure Mozart is turning in his grave….. but I think this is amazing!


4) Variety of ways to input


MIDI signals can be sent via all manner of input devices which can be designed for the musician’s requirements.

Often we think of a keyboard when we think of a MIDI instrument but it could be pretty much anything.

Many electronic drum kits, for example, send messages via MIDI. If you hit the drum harder you will get a higher velocity value for example, and as with a keyboard this value is noted in the DAW.




Of course, most of the time where there are advantages there are some disadvantages. These are all down to personal taste and if you get good virtual instrument plugins or samples maybe they won’t be disadvantages to you.


1) Sounds aren’t realistic


Many people argue that virtual instruments and samples will never sound the same as the real live thing. This may be true for certain instruments. But for many, we home musicians on a budget simply don’t have the equipment or studio setup to match what can be achieved through MIDI.

To get great live drum recordings for example, one must have a room with great acoustics, the correct microphone setup and a drum kit that is in tune. And even if you think you have all that, you may find that it doesn’t sound much better than MIDI drums after all.

Yes in an ideal world we would record everything live, using audio tracks, but in a home studio on a budget MIDI still makes the most sense.


2) Can’t be used to transmit vocal data


As it is only a series of numbers, it probably won’t surprise you that vocals cannot be sent via MIDI. If they did, I imagine they would sound very strange indeed.

Yes, you will still need to record your vocals to audio files, usually using an XLR input not MIDI.


3) Only accurate if the playback device is the same as the one used for production


The playback relies on the receiver of the file also having the relevant digital instrument or plugins loaded into their DAW for your track to sound the same as it does to you. This can be frustrating when sharing files amongst fellow musicians.

So there you have it, a short guide to the world of MIDI. MIDI is a really useful tool for the home studio and I’m sure you will be using it to make amazing songs in no time.

Rob Wreglesworth

Rob has come to terms with the fact he will probably never be a famous rock star....but that hasn't stopped him from writing and recording music in his home studio. Rob has over 15 years experience of recording music at home.

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