The audio and MIDI devices to be used by MultitrackStudio can be selected in the Studio menu's Devices window.
MultitrackStudio Pro supports up to 140 audio channels. Lower editions support two audio channels.
On Mac there's just one audio driver type: Core Audio.
Audio Output Control
The Audio Output Control (available from the Studio menu) can be used to set the properties (channel selection, levels, etc.) of the audio output device. The controls depend on the audio driver type and devices used.
MultitrackStudio Pro supports up to four MIDI In devices, and up to four MIDI Out devices. Lower editions support one MIDI In device, and up to two MIDI Out devices.
MPE MIDI Input
There's an MPE check box for each MIDI Input Device. MPE (MIDI Polyphonic Expression) uses separate MIDI channels for each note, so each note can have its own pitch bend, brightness, and aftertouch controls. MultitrackStudio maps these controls to MIDI 2.0 per-note pitch bend / per-note brightness and MIDI 1.0 poly aftertouch, respectively.
If an MPE keyboard sends RPN messages to change the MPE configuration, the MPE check box will be updated accordingly.
In most cases, the incoming MPE data will go to MIDI channel 1. If an MPE keyboard sends a different configuration, it could go to MIDI channel 16 or both 1 and 16 (two MPE zones).
Tip: do not use the MPE option if you don't have an MPE keyboard. There's no benefit and many potential problems.
MIDI Out Device Options
The Options button in the MIDI Out Devices section pops up the MIDI Out Device Options window. It contains settings regarding sync code and recording connections.