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Simplifying MIDI - Musical Instrument Digital Interface

If you have already tweaked any keyboard, you’d probably already seen the word MIDI. My intention here is to clear up what it is and what is MIDI for.

10 Reasons why you should learn about MIDI:

  1. To help you setup and program musical keyboards;

  2. To help you setup DAWs (Digital Audio Workstation);

  3. To help you setup music sheet softwares;

  4. To setup VSTis (Virtual Instrument Plugins);

  5. To connect your keyboard to another one;

  6. To connect your keyboard to a module;

  7. To blend presets between synthesizer keyboards and workstation keyboards;

  8. To record on workstation keyboards;

  9. To setup expression pedals;

  10. To control any piece of equipment with a MIDI interface.

If at least one of the reasons above is useful for you, I highly recommend that you keep reading. At the end of it, if you have any comment or suggestion about it, please, leave a comment.

You will notice that MIDI is connected to a series of other important concepts that will also be mentioned.

MIDI means Music Instrument Digital Interface. It was a protocol developed in the 80s to allow communication between electronic musical instruments or any other device with this interface. MIDI itself does not produce any sound. What MIDI does is send a series of messages saying “the note was played”, “the note was released”, “the note was played strongly”, “the note was played softly”, “pedal pressed”, “pedal released”, “raised volume”, etc.

Those messages are sent electronically in the form of “bits”. They are received by musical instruments to produce sounds according to what is requested. We will get into the details below.


Before we proceed with MIDI messages, it’s important to understand what a MIDI Interface is. Let me explain: This concept works for anything related to digital electronic equipment, such as audio interfaces, video interfaces or MIDI interfaces.

WHAT IS INTERFACE? It is the system by which two environments can communicate. The most common interface example is the electrical outlet. This is the way any equipment can be connected to the electric power grid.

An interface is not just about two connectors, but about the capacity to read information from both environments. So, when we say that any device has a MIDI interface, it means it understands MIDI, therefore, it’s able to receive or send information in the MIDI format.

Nowadays, most digital musical devices (mostly keyboards) with MIDI interfaces usually provide the following connectors:

  • IN

  • OUT

  • THRU (bypass the signal)

  • USB (In and Out available through a computer driver)

To connect MIDI equipment, you must respect the signal flow, which means “who sends” and “who receives”. It makes no sense to connect MIDI OUT x MIDI OUT, or MIDI IN x MIDI IN. See some possibilities below.

(Controller) MIDI OUT - > MIDI IN (Synthesizer)

(Synthesizer) MIDI OUT - > MIDI IN (Synthesizer)

(Controller) MIDI OUT - > MIDI IN (Module)

(Controller) MIDI OUT - > MIDI IN (Audio Interface) - > USB (Computer)

(Controller) MIDI OUT - > USB (Computer - Midi In)

(Workstation Keyboard) MIDI OUT - > USB (Computer - Midi In/Out)

Following the arrows, it’s possible to identify the information flow sent or received. When there’s OUT -> IN, the information is sent (TX) and when you have the IN -> OUT, the information is received (RX).

MIDI Messaging

This is the most important part to understand how MIDI messages work. Let 's go one by one.


When you play any key, this message is sent. It consists in two parts:

NOTE - Which key was pressed (Ex: C3)

Velocity - The intensity used to press this key. Goes from 0 to 127

Most keyboards with key sensitivity allow the velocity curve setup. This is how the keyboard responds to the key playing.

If the curve is smooth, it means even if I play softly, the keyboard will reproduce the note with high velocity levels.

If the curve is intense, that means to reach a high velocity level, you need to press the key really hard.


When you release a key, a message is also sent. It’s the NOTE OFF. This message allows the note played to be stopped.

Like the previous one, the NOTE OFF also sends note and velocity. Velocity, in this case means how fast the note was released.

Those concepts can be easily seen, if you open any .mid file in any sequencer software with a piano roll.


It is present in some keyboards. It consists in the continuous press of the key, right after it’s pressed. The intention of it is to deliver some expression, and it can be read in many different ways by the instrument that receives the message, to change volume, tone, vibrato, etc. Aftertouch can go from 0 to 127.

Pitchbend is a control that can be found in most keyboards. It looks like a “wheel” or a small bar, like a lever, usually on the left side of the instrument. As the name says, PITCHBEND can pro

duce pitch variations. This variation is constant and can be less than half a tone. The variation size can be preset in the target instrument. Pitchbend can go from 0 to 127. The standard position is 64.


Control messages are essential to assure independence and fidelity reproducing virtual instruments. Most keyboards have a series of controllers available. It means any piece of rig can receive functions and parameters. For each control, a range from 1 to 127 is designed.

There are some standard controls for most keyboards and virtual instruments. The initials CC are often used to identify a control. See above a list of the most common presets.

  • CC1Modulation (modulation wheel): Usually generates vibrato or tremolo effect in the target instrument.

  • CC7 – Volume

  • CC11Expression (expression pedal) – Usually associated with the instrument volume

  • CC64 – Sustain (sustain pedal)

Some virtual instruments (VSTi) allow setting controls to the instrument parameters. For example, Kontakt allows you to set a controller to any parameter on the instrument key. This is possible right-clicking and choosing learn CC#. When you access this controller (knob, fader or pedal), on the keyboard, Kontakt will recognize it automatically.


It’s very important to understand the MIDI channels. The current protocol works with up to 16 channels by which the messages are sent.

The channels allow MIDI messages to be sent to different instruments simultaneously. It’s possible to place a piano on channel 1, strings on channel 2 and drums on channel 10, for example.

Most rigs with MIDI interface allow you to set input channels (RX reception) and output channels (transmission - TX)

If there’s a controller keyboard connected to another instrument, you must know the output channel of the controller and also the input channel of the other instrument. If you set your controller to send on channel 1, you must be sure that the other instrument is set to receive on channel 1 as well.

Sequencer softwares and Daws have MIDI tracks where you can set the input channel for each track.

DAWs designed for live performance usually have the option of MIDI mapping. This way, it’s possible to customize the channel setup between virtual instruments inside the software. If the controller keyboard sends messages only for channel one, it’s possible to set the DAW to play channel 1 on channels 1,2 and 3.

The concept behind those MIDI mapping examples is the possibility of blending different tones, different virtual instruments.

Good job! Now that you can understand the basic MIDI concepts, I suggest you try using a DAW on your computer and start trying it.

If you found this useful, please check for the following article about MIDI programming.


This is only a joke about a function that can be found in most VSTIs, DAWs and MIDI controllers: panic! It’s a tool used to reset the MIDI messages, very useful in case of crashes or bugs that leave undesired notes on your MIDI sequence.


Many virtual instruments are misjudged for not having an organic execution. The VSTIs usually offer tone variations using the velocity. Sometimes, to be realistic and have a good expression, it’s required to change the velocity curve on your keyboard. For piano tones, for example, a hard curve makes a world of difference.


Some VSTIs try to reproduce real instruments. Those have articulation keys. Those are keys that do not produce sounds, but they change the note behavior. In the following example, the lower keys alternate between violin skills and articulations.



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