MIDI messages [Light] [Beginner] [Professional] [Notation] [Composition Light] [Composition Pro] [Drums and Percussion] [Guitar] [Choir] [Keyboard] [Soloist]

The purpose here is not to explain the detailed structure of the MIDI language messages, but simply to understand the principles used to exchange musical information.

The most significant messages are those specifying when a note is pressed or released with the musical keyboard. When you press a key on your musical keyboard, 3 numbers are sent:

(Note ON + channel) + (Key number) + (Velocity)

• Note ON simply means that the key has just been pressed and the channel is a sort of address (we will explain this further).
• Key number specifies which key is being pressed. The keys has a standard number between 0 and 127, the lower C of the treble clef being number 60.
• Velocity is the force with which the key was hit. You may indeed press a key gently or very sharply. Many keyboards record this force and send it in MIDI. The synthesizer receiving this note plays it more or less loudly according to the value of the velocity (between 0 and 127, 64 being a value often sent by default when the keyboard is not sensitive to velocity).

A similar message is sent when you release the key:

(Note OFF + channel) + (Key number) + (Velocity)

• Note OFF means that a key has been just released.
• Key number specifies which key was released.
• Velocity is seldom used or placed to 0.

When you play on a musical keyboard, each note thus generates two MIDI messages. The first is sent when you press a key and the second when you release it. A piece of music generates a constant flow of MIDI messages.

Besides note messages, there is a whole series of various MIDI messages used to modify the characteristics of the performance. We will examine two types of messages here, the program changes and the MIDI controllers.

A program change is a MIDI message requiring the synthesizer to change its sound. It contains a number between 0 and 127, which specifies the number of the desired sonority. Each synthesizer has a numbered list of sounds it can generate. When it receives a program change, the synthesizer selects the sound corresponding to the given number.

If a synthesizer has a flute sound bearing number 21 and if you want to play flute with your keyboard, you need to send a program change with number 21. The notes you will then play will be heard with a flute sonority. You can find the list of sounds of your synthesizer in its instruction manual. These lists may be specific to each synthesizer.

A very widespread standard has been adopted by manufacturers as a compatible mode. It is the GM (General Midi) standard. It establishes a unique correspondence between the program change numbers and the sounds. Thus a piano sound bears number 1, the trumpet bears number 57, etc. When Pizzicato plays a score, it first sends a program change before starting to play the notes, so that the synthesizer knows with what sonority those notes must be played.

MIDI Controllers are messages used to change the way in which sounds are generated in the synthesizer. There are 128 different controllers, but only a small part of it is in common use.

The volume controller (number 7) for example, determines the output volume of the instrument sound. This message specifies to the synthesizer the volume the sound must have. When it receives a volume controller, the synthesizer uses it to fix the sound level of the instrument. The value can vary between 0 (the sound is not audible) and 127 (maximum level). It is used to regulate the general balance between instruments.

Other controllers allow to change the balance (stereophonic effect: instrument on the left or on the right), to add a vibrato in the notes, etc.

One of the controllers simulates the effect of the hold pedal (right side pedal of a piano). When it is activated, it holds the notes until the pedal is released.