Apple Logic Pro 9 - Manual (Page 40)

If the MIDI interface connected to your computer only offers one MIDI output, you need
to connect the MIDI In of the second tone generator to the keyboard MIDI Thru port. A
third device can be connected to the MIDI Thru of the second unit, and so on.
Computer
MIDI interface
Out port
Out port
Keyboard
In port
In port
In port
In port
MIDI Thru port
Tone generator 2
Tone generator 3
The MIDI Thru port replicates the signals coming into the MIDI In port of the device. It is
preferable to use a direct connection from the computer MIDI Out to a device, rather
than chaining too many units, one after the other. Doing so can cause timing problems
in the chain, if numerous MIDI commands are sent quickly. This is due to the slight delays
introduced by each MIDI In to MIDI Thru transaction. As such, a multi input/output MIDI
interface is recommended in studios with several MIDI tone generators and controllers.
Using Multi-Channel MIDI Devices
Most modern MIDI tone generators can simultaneously receive MIDI data on multiple
MIDI channels (multi-timbral MIDI devices). Each MIDI channel can be assigned a tone or
sound, such as piano, strings, bass, and so on.
To take full advantage of the capabilities of each connected multi-timbral device, you
need to use separate MIDI Out ports (from the computer MIDI interface to the MIDI In
ports) for each device. To explain further, imagine a scenario where:
• There are four MIDI tone generators that are capable of receiving data on multiple
channels.
• All devices can receive on all 16 MIDI channels.
• There is only one MIDI Out from the computer, and all devices are daisy-chained via
MIDI Thru to MIDI In connections.
Logic Pro is capable of channelizing MIDI data (routing it to MIDI channels 1 to 16) and
is also capable of sending this channelized data to specific MIDI Out ports. Unfortunately,
in the scenario above, there is only one MIDI Out port available.
40 Chapter 2 Setting Up Your System