Stand-alone Virtual Instruments
A stand-alone virtual instrument is one that runs as a separate application, side by side with Digital Performer (instead of as a plug-in running inside Digital Performer).
Digital Performer does not require any additional preparation for use with CoreMIDI-compatible virtual instruments. (CoreMIDI is the "under-the-hood" portion of Mac OS X that handles MIDI services for MIDI hardware and software.)
If a virtual instrument operates as a separate application, run it concurrently with Digital Performer, and any MIDI inputs and outputs that it publishes to CoreMIDI will appear in Digital Performer's MIDI input and output menus. Similarly, the instrument's audio outputs will appear in the input menus of Digital Performer's audio tracks.
If the virtual instrument supports ReWire, then it uses the ReWire protocol to exchange MIDI and audio data with Digital Performer.
If the virtual instrument operates as a plug-in inside Digital Performer, open it as described in Virtual Instrument Plug-ins. When you open the plug-in, its MIDI inputs and outputs appear in Digital Performer's MIDI I/O menus.
Interapplication MIDI
Most applications that share MIDI input and output with Digital Performer publish their own virtual MIDI inputs and outputs, which automatically appear in Digital Performer's MIDI input and output menus. Most of the time, you can use the inputs and outputs provided by these other applications.
There may be times, however, when other applications require Digital Performer to publish inputs and outputs. Use the Interapplication MIDI window (Setup menu) to create them.
Click the Add buttons to create an input or output. To rename them, double-click the name. To remove an input or output, click it and click Delete.
Each input or output acts like a virtual MIDI cable, providing sixteen MIDI channels. Inputs appear by name in any menu in Digital Performer that displays MIDI inputs; outputs appear by name in any Digital Performer menu that displays MIDI outputs. For example, if you wish to send data from a Digital Performer MIDI track to another application, assign the track's output to a Digital Performer MIDI output.
Digital Performer's interapplication MIDI inputs and outputs are published to all MIDI applications that support macOS's built-in MIDI services. A Digital Performer output appears as an input in other applications; conversely, a Digital Performer input appears as an output to other applications.
The software synthesizer
macOS provides a basic software synthesizer that supplies a general MIDI sound set. To make this virtual instrument available as a MIDI destination and sound source in Digital Performer, check the box provided in the Interapplication MIDI window (Setup menu), and give it a name. The name you choose then shows up as a MIDI output destination in Digital Performer and other CoreMIDI-compatible applications (when Digital Performer is running). To specify the audio output destination for the software synthesizer (i.e. where you'll hear it), go to the Audio tab in macOS's Audio MIDI Setup utility and choose the desired Default Output destination. The Render quality menu lets you choose the audio quality for the instrument playback. Higher quality places higher demand on the computer's CPU resources.