You need some kind of 'Virtual MIDI cable' to connect two MIDI apps with each other. MacOS / OS X doesn't come preconfigured with such a connection, but it is pretty easy to set one up. Just follow these steps: Launch the 'Audio MIDI Setup' of macOS; Open the 'Window' menu and click on 'Show MIDI Studio' Double-click on the IAC Driver icon. Each interface, with each of its MIDI ports numbered, will show up here.If for some reason you don't see your device in this window, just clickthe Add Device button for each missingMIDI device that's connected to your interface.This will create a new icon for a new external device.I'm going to go ahead and add this,as a Korg Triton.We can double-click to change the device nameand you can select from the manufacturers list. The MIDI project settings determine the behavior of the MIDI inputs and outputs. The MIDI project settings comprise the General, Input Filter, and Chase panes. In the Audio MIDI Setup app on your Mac, choose Window Show MIDI Studio. In the MIDI Studio window, click the Choose MIDI Configuration pop-up menu (it may show Default), then choose New Configuration. Enter a name for the new configuration, then click OK. To add a new external MIDI device, click the Add button in the MIDI Studio toolbar.
Audio MIDI Setup User Guide
If you use MIDI devices or a MIDI interface connected to your Mac, you can use Audio MIDI Setup to describe the configuration of your MIDI devices. There’s a default configuration already created, but you can set up your own.
You can use this configuration information for apps that work with MIDI, such as sequencers, to control your MIDI devices.
Note: Make sure your MIDI devices are connected to your Mac. If you’re using an interface device, connect any other MIDI devices you’re using to the interface. Also check that any software provided by the manufacturer of the MIDI devices has been installed. For more information, see the documentation that came with your devices.
View a MIDI configuration
In the Audio MIDI Setup app on your Mac, choose Window > Show MIDI Studio.
In the MIDI Studio window, click the Choose MIDI Configuration pop-up menu (it may show Default), then choose the configuration you want to view.
In the toolbar, click the following buttons to change how the configuration is shown:
Show Icon View : Devices in the configuration are shown as icons. If a device isn’t connected, its icon is dimmed. To view information about a device, such as channel properties and ports, and to add or remove ports, double-click the device’s icon.
Show List View : Devices in the configuration are shown in a list, organized by type (such as Interface or External Device). If a device isn’t connected, it’s dimmed. To filter which devices are shown, click the Show pop-up menu, then choose an option (such as Online or Connected). To view information about a device, double-click the device. To view its ports, or to connect or disconnect devices, click the device’s disclosure triangle.
Create a MIDI configuration
In the Audio MIDI Setup app on your Mac, choose Window > Show MIDI Studio.
In the MIDI Studio window, click the Choose MIDI Configuration pop-up menu (it may show Default), then choose New Configuration.
Enter a name for the new configuration, then click OK.
To add a new external MIDI device, click the Add button in the MIDI Studio toolbar.
To set properties and add or remove ports for the MIDI device, double-click the device, or select it, then click the Device Info button in the toolbar.
In the Properties window, do any of the following:
Describe the device: Enter a name for the MIDI device; the name appears in apps you use with the device. If you know the manufacturer and model, you can enter those.
Change the device icon: Click the MIDI device’s icon to open the Icon Browser, select a different icon to represent the device, then click the new icon to close the Icon Browser.
Change the device color: Click the color well, select a different color to use for the MIDI device, then close the Colors window.
Set the device channels and other properties: Click Properties, then click the channels to use for transmitting and receiving audio. To deselect a channel, click it again. Also select whether to use the MIDI Beat Clock, the MIDI Time Code, or both, then select other features.
Add or remove ports: Click Ports, click the Add button below the list of ports, then specify the MIDI In and MIDI Out connectors for the port. To delete a port, select it in the list, then click the Remove button .
Select MIDI-CI profiles for interface devices: If an interface device supports MIDI-CI, click MIDI-CI to see the profiles available on each channel. To turn a profile on or off, select or deselect its checkbox.
Click Apply.
Repeat steps 4 through 7 for each MIDI device you want to include in the configuration.
In the MIDI Studio window, specify the connection between MIDI devices:
In Icon View , drag the In or Out connectors at the top of a device icon to the corresponding connector on another device icon.
In List View , click a device’s disclosure triangle, click the Port disclosure triangle, click the Add Connection icon, then use the pop-up menus to specify the connections.
If you have a MIDI interface connected to the USB port on your Mac, it should appear in the MIDI Studio window. If it doesn’t, see If a connected MIDI device isn’t shown.
You can’t specify a “MIDI thru” connection between two MIDI devices. To indicate a MIDI thru connection, connect the two MIDI devices to the same port of the MIDI interface device.
Edit a MIDI configuration
In the Audio MIDI Setup app on your Mac, choose Window > Show MIDI Studio.
In the MIDI Studio window, click the Choose MIDI Configuration pop-up menu (it may show Default), then choose Edit Configurations.
Select a configuration, then click Duplicate, Rename, or Delete.
When you’re finished making changes, click Done.
Mac Midi Player
Audio MIDI Setup User Guide
Use Audio MIDI Setup to set up audio input and output devices, such as microphones and multichannel audio interfaces. You can also use it to route audio from iOS and iPadOS devices directly into your Mac.
Mac Midi Setup
Available settings in Audio MIDI Setup depend on the audio device you’re using. For example, you can adjust the volume for each channel your audio output device has available.
Connect your audio devices to your Mac and, if necessary, install any software included with the devices.
In the Audio MIDI Setup app on your Mac, in the sidebar of the Audio Devices window, select a device.
Note: For iOS and iPadOS devices, first click Enable, then select the device. You may be asked to unlock your device with a passcode or to trust the device.
Control-click the device, or click the Configure Selected Device pop-up menu at the bottom-left of the sidebar, then choose how the device is going to be used:
For sound input: Choose Use This Device for Sound Input.
For sound output: Choose Use This Device for Sound Output.
For playing system sounds: Choose Play Alerts and Sound Effects Through This Device.
On the right side of the Audio Devices window, choose the options available for the device you selected:
In most cases, “Clock source” is set to the default.
Click the Format pop-up menu, then set the sample rate and bit depth. Make sure they match the appropriate settings for your audio device.
If your Mac supports the hardware sample rate converter, the Hardware Rate Converter pop-up menu is available in the Input pane. When you choose Automatic from the pop-up menu, the hardware sample rate converter is turned on if the audio samples coming in are PCM and formatted according to the international standard IEC 60958-3. The hardware sample rate converter is turned off if the input stream is encoded. You can also choose Enable or Disable from the menu, to keep the hardware sample rate converter turned on or off.
If software volume control is available for your device, the Volume sliders appear blue to indicate that they’re active. Drag the sliders to set the volume for each channel.
To set up a surround (multichannel) speaker configuration, click Configure Speakers, then set up the configuration.