MIDI |
The purpose of MIDI [Light] [Beginner] [Professional] [Notation] [Composition Light] [Composition Pro] [Drums and Percussion] [Guitar] [Choir] [Keyboard] [Soloist] MIDI means Musical Instrument Digital Interface. Its
purpose is to transmit the actions executed with a musical
keyboard in a digital form. It is a universally adopted language to
exchange musical information between synthesizers and computers. When you hit a note on a musical keyboard,
the keyboard immediately sends a message to its MIDI output.
This message communicates for example that the C-3 note has
just been pressed. When you release the note, another message
is instantaneously sent to express that the C-3 note is
released. If a pedal is connected to your
synthesizer, the fact of pressing or releasing this pedal
also sends a MIDI message expressing this action. Similarly,
when you move a lever located on your keyboard, it also
generates MIDI messages. In other words, each action executed by the
performer on his keyboard is translated and instantaneously
sent as a MIDI message to the devices connected to it by a
cable. These standard MIDI messages only contain
numbers which characterize the type and the content of the
message. Those numbers are instructions which command a
synthesizer what to play and how to play it. It is not a
sound which goes through a MIDI cable, but only a set of
instructions used to control a musical synthesizer. When the computer wants to play a score on
a synthesizer, it simply sends the necessary MIDI
instructions to it, and the synthesizer produces the sounds,
not the computer. The computer simply replaces the performer. Therefore, the sound quality depends only
of the synthesizer which executes the MIDI commands. MIDI
does not have a "sound quality". A MIDI message
simply gives the order "Play this note!" and the
synthesizer executes it with its capabilities.
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) A similar message is sent when you release
the key: (Note OFF + channel)
+ (Key number) + (Velocity) 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.
MIDI channels [Light] [Beginner] [Professional] [Notation] [Composition Light] [Composition Pro] [Drums and Percussion] [Guitar] [Choir] [Keyboard] [Soloist] Until now we have considered that only one
instrument was playing. How to play a score which contains 5
different instruments? A MIDI connection actually contains 16
independent MIDI channels. It is like
a highway with 16 tracks, where MIDI messages may circulate
on a track without affecting the messages of the other
tracks. A
multitimbral synthesizer is able to
generate several different sonorities at the same time, like
the piano, the guitar, the battery, etc. Most current
synthesizers allow this. The 16 MIDI channels connected to the
synthesizer behave as if there were 16 different synthesizers
at the end of the cable. Pizzicato can work with the various
channels by assigning each instrument to a channel and by
sending the notes on the corresponding channels. When one of the above MIDI messages is
sent, the channel is specified. Let us take a simple example: a piano, bass
and battery score. Pizzicato assigns channel 1 to the piano,
channel 2 to the bass and channel 10 to the battery (most
synthesizers reserve channel 10 for percussions). Before
starting to play, Pizzicato sends the following program
changes: From this moment, all notes sent on channel
1 will be played with a piano sound. Similarly, notes sent on
channel 2 will play the bass and notes sent on channel 10
will activate the battery. When Pizzicato plays the score, it assigns
itself the MIDI channels to use, according to the
possibilities of your synthesizer. After having sent the
program changes, the notes of the piano staff are sent on
channel 1, the notes of the bass on channel 2 and the notes
of the battery on channel 10. When you change the volumes and the options
of the instruments view, Pizzicato sends the messages
corresponding to the channels assigned to each staff, for
example to decrease the volume of the bass, or to add
reverberation on the battery, etc. A detailed and complete explanation of the
MIDI language would be out of the scope of this manual.
Nevertheless, you have here an outline of MIDI, well
sufficient to use Pizzicato, because in most current
functions, Pizzicato completely handles MIDI for you.