Playback and Recording : MIDI Recording : MIDI Thru : The Default Thru Instrument

The Default Thru Instrument
In addition to any MIDI tracks that are record-enabled, you can also route MIDI to the Default Thru Instrument. This saves the extra steps of creating a MIDI track and record enabling it to hear a particular MIDI device and channel.
Unlike MIDI tracks, which only receive MIDI from the device and channel assigned to its MIDI Input selector, all incoming MIDI data is routed to the Default Thru Instrument.
If the Default Thru Instrument is assigned to a record-enabled MIDI track, Pro Tools only routes incoming MIDI to the record-enabled track.
To configure a default Thru instrument:
1 Choose Setup > Preferences.
2 Click the MIDI tab.
3 Do one of the following:
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Select a specific device from the Default Thru Instrument pop-up menu to play MIDI through on that device by default.
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Select Follows First Selected MIDI Track to have MIDI preview assignment follow MIDI track selection. When multiple MIDI tracks are selected, previewing uses the topmost MIDI track in the Edit window or the leftmost MIDI track in the Mix window.
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To disable the Default Thru Instrument, select None.
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The Default Thru Follows First Selected MIDI Track Selection option also lets you play an instrument without having to create and record-enable a MIDI or Instrument track.