Some MIDI messages sent by your keyboard controller (or other MIDI device) are “passed through” to any channel strips in the MainStage concert that are mapped to the same controller (or device). Whether or not MIDI messages are passed through depends on the following conditions:
If there is no screen control in your layout assigned to receive the message type sent by the controller, the messages are passed through.
If a screen control for that MIDI message type exists, and the MIDI Thru parameter for the screen control is set to Automatic or to the input device, the messages are passed through. This is the default for screen controls set to receive volume, pan, expression, sustain, modulation, pitch bend, and aftertouch messages.
If a screen control for that MIDI message type exists, and the MIDI Thru parameter for the screen control is set to “Do not pass through,” the data is not passed through. This is the default for most other screen controls.
The reason for these exceptions is so that when you add a screen control for a modulation wheel or a sustain pedal, for example, it “automatically” responds to the appropriate MIDI message type, without your having to configure it further. If you want to have the screen control respond to a different type of MIDI message, you can choose another MIDI message type from the Number pop-up menu in the Screen Control Inspector.
Incoming MIDI messages that are passed through are passed to any channel strips mapped to the same device sending those messages (that is, to the keyboard controller you are using to “play” those channel strips). If there is no matching device, the MIDI messages are sent to all channel strips.
You can also filter incoming MIDI messages for individual channel strips. For information on filtering MIDI messages, see Filtering MIDI Messages.