Apple Logic (1.1) - Manual (Page 89)

Chapter A Audio and MIDI Basics 89
MIDI Channels
MIDI is divided into 16 logical “channels”. Each channel is identified by a special channel
number message that is sent with the other MIDI messages. Most keyboards can
generally be set to transmit on any one of the 16 MIDI channels. A MIDI sound
source—such as your synthesizer or sound module—can be set to receive on a specific,
or multiple, MIDI Channel(s).
Devices capable of receiving on multiple MIDI channels simultaneously are said to be
“multi-timbral”. The term literally means “many sounds”, which can be a little confusing,
as most synthesizers are obviously capable of producing many sounds. Not all
synthesizers, however, are capable of producing many sounds at the one time. This
capability means that a suitably-equipped MIDI keyboard or module could be used to
produce all of the drum, bass, piano, string, and brass sounds in a performance.
In this scenario, each part, or instrument—drums, piano, strings, and so on—will be
assigned to a specific MIDI channel. Given the 16 logical MIDI channels available to
each MIDI port and a multi-timbral synthesizer, up to 16 different “instruments” can be
played simultaneously. Most modern MIDI keyboards and sound modules are multi-
timbral.
Important: In all MIDI systems, the sound module must be set to receive on the
channel (or channels in multi-timbral devices) which match the channel(s) that the
keyboard controller (or Logic) is transmitting on, in order to play sounds. If the
channels do not match, the receiving device will not play.
As an example: Imagine a 4-way multi-timbral device (a device capable of receiving on
4 MIDI channels simultaneously) is receiving song data from Logic—with tracks
assigned to channels 1, 2, 4, and 5.
The device itself is set to receive on channels 4 to 8. In this case, only the song’s MIDI
data sent on channels 4 and 5 would be “seen” by the device, and subsequently played.
The MIDI data sent on channels 1 and 2 would be ignored.
As you can see from the above example, each channel needs to be “tuned in” to a
corresponding channel sent from Logic. This, if you use a little imagination, is not unlike
tuning in a TV or radio channel. If the channel isn’t tuned properly, you won’t see or
hear anything … and neither will your sound module!