Tuesday, May 5, 2009
Channel Messages & System Messages
There are two kinds of MIDI messages ; one is Channel Messages and another is System Messages. Channel Messages are messages which have channel numbers, such as keyboard performance messages. System Messages have nothing to do with channels, and controls the entire system.
System Messages include the messages that synchronize two or more instruments, and the messages which is used exclusively in each individual manufacturer.
Let's have a closer look at these messages.
Channel Messages include Voice Messages and Mode Messages.
Voice Messages (Performance Information) a Note On/Off Messages
These most basic MIDI Messages are Note On and Note Off Messages.
Note On Message include what key is how hard (velocity amount) pressed, and Note Off is what key is released.
All keys have different numbers (key numbers) which can also be assigned to the drum voices of a rhythm machine.
Program Change Messages
Many of today's synthesizers can store the tone colors (patch program) in the memory. These patches can be called when required usually by pushing buttons on the panel.
The Program Change Messages can also call the patches from memory.
This applies to the patch program in the memory of the MIDI effect units as well.
Each instrument, however, has a different method of assigning numbers. So, to be able to cope with the patches of all kinds of MIDI devices, MIDI Program Change numbers are simply from 0 to 1 27.
These numbers are differently assigned to the patches of each MIDI instrument.
The owner's manual of each instrument will always show how the Program Change numbers correspond to its patches in memory.
Usually, on the left side of the synthesizer, a lever or a wheel is provided to elevate the pitches of generated sounds.
It serves to create an expression like the "choking" on a guitar.
The movement of the bender lever can also be communicated as Pitch Bender Messages through MIDI.
The maximum range of this pitch bender effect, however, is not included in the Pitch Bender Messages, therefore should be set on each instrument.
After touching the key in a normal playing manner, you may press the key hard without releasing it. The obtained effect is that the vibrato or brilliance changes.
This is called After Touch effect which can also be communicated as a part of MIDI information. Which of the vibrato or brilliance is to be controlled can be selected on each instrument.
Synthesizers usually have controllers and switches which can be operated during performance. e.g. On/Off of the vibrato, portamento and hold functions, On/Off of the damper or soft pedal of an electronic piano, etc.
These actions can be communicated as Control Change Messages through MIDI.
The Mode Messages work to select one of the four modes (OMNI ON:POLY, OMNI OFF:POLY, OMNI ON:MONO, OMNI OFF:MONO) which have been explained on PART 4.
A master MIDI device can change the modes of the slave device.
In most of the Roland synthesizers, the receiver defaults to OMNI ON & Poly Mode at power up, then the transmitter sends the OMNI OFF and Poly Messages to the receiver on the set channel.
So, first set up the two synthesizers with MIDI cable, and turn the receiver on, then the transmitter.
This changes the receiver's mode according to the Mode Messages (POLY & OMNI OFF) transmitted if their channels are matched.
The Mode Messages also serve to stop the sound caused by receive error or to internally separate the keyboard from the sound source.
The System Messages are the messages which can be sent without setting a MIDI Channel. e.g. messages that synchronizes a rhythm machine with a sequencer.
The System Messages also include the messages that resolve operation troubles, e.g. when the unit keeps crying because the MIDI cable is disconnected during operation.
MIDI is an international standard, but each manufacturer also has its own messages to remain originality of each product.
This is called Exclusive Messages and used in the tone color data of synthesizers or for communication of the sequencer data, etc.
Exclusive Messages make it possible to synthesize while watching the monitor display of a computer, and to copy tone color data to other synthesizer.
To avoid confusion of the Exclusive Messages among different manufacturers, the idea of ID Numbers is introduced.
An ID Number is distributed to each manufacturer, and given to its Exclusive Messages, allowing the connected instrument or computer to recognize it.
Although MIDI devices can communicate various kinds of messages, the receiver does not necessarily need to recognize all messages sent from the transmitter.
Sometimes it may even be trouble to recognize all. For instance, the After Touch or Pitch Bender Messages consume too much memory when entered into a sequencer.
Also, it may be sometimes necessary to ignore the Program Change Messages.
In such cases, the Function Switches usually located on the back of the device can be effectively used.
Labels MIDI Basics