How to Route MIDI Between Apps on macOS

Last updated: March 2026

This guide explains how to route MIDI between apps on macOS — whether you are connecting a keyboard to a DAW, routing output between two DAWs, or building complex multi-app setups. macOS provides the IAC (Inter-Application Communication) driver for basic MIDI routing, but it has no visual interface and limited flexibility. Midilize is a visual MIDI routing utility that replaces hidden buses with a drag-and-drop patch-graph interface, giving you a clear view of every connection in your setup.

What is MIDI routing?

MIDI routing is the process of directing MIDI data from a source — such as a hardware keyboard, a DAW track, or a software instrument — to a destination such as a synthesizer, another application, or a virtual instrument. On macOS, MIDI devices and apps communicate through MIDI ports. A MIDI router sits between source and destination, forwarding, filtering, or transforming the signal as it passes through.

Common routing setups include:

• Keyboard to DAW — the simplest setup: one source, one destination
• One keyboard to multiple DAWs — split the signal to reach several apps simultaneously
• DAW output to a hardware synthesizer
• Two DAWs exchanging MIDI data over a virtual bus
• Controller to multiple destinations, each filtered to a specific channel

The macOS IAC driver

macOS includes the IAC (Inter-Application Communication) Driver, a built-in virtual MIDI bus that lets apps send MIDI to each other. To enable it:

1. Open Audio MIDI Setup (in /Applications/Utilities)
2. Go to Window > Show MIDI Studio
3. Double-click the IAC Driver icon
4. Check "Device is online"
5. Add additional ports if needed using the + button
6. Rename ports by double-clicking their names for clarity

Now any app can send MIDI to the IAC bus, and any other app can receive from it. In your DAW, select "IAC Driver Bus 1" (or your named port) as the MIDI output. In the destination app, select the same port as its MIDI input.

Limitations of the IAC driver

While the IAC driver works for basic routing, it has significant drawbacks for complex setups:

• No visual overview — you cannot see which apps are connected to which ports
• No filtering — all MIDI data on a port goes everywhere; you cannot filter by channel or message type
• No transformation — you cannot transpose, remap, or modify MIDI data in transit
• Naming confusion — managing multiple IAC ports with generic names quickly gets confusing
• No monitoring — you cannot see what is actually flowing through the bus without a separate tool
• No fan-out control — routing one input to multiple destinations requires workarounds

Visual routing with Midilize

Midilize replaces the invisible IAC workflow with a visual patch-graph interface. Your entire MIDI routing setup appears as nodes and cables on a canvas. Here is how to set up a basic route:

Example: routing a MIDI keyboard to two DAWs

A common scenario is splitting a MIDI keyboard between two applications. In Midilize:

1. Add a MIDI In node for your keyboard
2. Add a Split node to divide by note range (e.g., below C4 and above C4)
3. Add two MIDI Out nodes, one for each DAW's virtual input port
4. Connect: Keyboard → Split → DAW 1 (low range) and DAW 2 (high range)

The entire setup is visible at a glance. No hidden buses, no configuration files.

Common routing scenarios

Channel-based routing: Route one device's output to multiple destinations, each receiving a different MIDI channel. Use the Channel Router node between MIDI In and multiple MIDI Out nodes, assigning each output a specific channel.

Velocity layers: Route quiet notes (velocity < 64) to one instrument and louder notes to another, creating dynamic switching between sounds based on how hard you play. Use the Double Filter tool configured to split on velocity.

CC filtering: Strip control change messages before sending to a synthesizer that misinterprets mod wheel or expression pedal data. Add a Filter node set to block CC messages on the connection to that destination.

Transpose and route: Transpose a keyboard up an octave using the Transpose tool, then route the result to a bass synth. Useful when a synth patch is pitched in the wrong register.

Multiple sources, one destination: Merge MIDI from two keyboards into a single output using multiple MIDI In nodes connected to the same MIDI Out node. All messages from both sources flow to the destination.

Virtual ports

Midilize can create virtual MIDI inputs and outputs directly from the Sources panel. Other apps see these as standard MIDI ports — the same as hardware devices or IAC ports. Virtual ports created by Midilize appear with the name you set, making them easy to identify in other apps. This replaces the need to manually configure IAC driver ports in Audio MIDI Setup.

Troubleshooting routing issues

MIDI not flowing between apps: Check that both apps have the same virtual port selected. In Midilize, verify the MIDI In and MIDI Out nodes show a green active indicator. Confirm the cables in the flow graph are properly connected (port to port, not floating).

MIDI feedback loop: If you route an app's MIDI output back to its own input, you create a feedback loop — notes trigger more notes infinitely. Monitor Mode will show an exponentially growing message count. Break the loop by removing the return cable or filtering the channel that feeds back.

Wrong channel at destination: Add a Channel Filter node between MIDI In and MIDI Out to block unwanted channels, or add a Set Channel node to force all messages to the correct channel before they reach the destination.

Destination app not seeing the virtual port: Restart the destination app after creating a virtual port in Midilize. Some apps only scan for MIDI devices at launch. Midilize must remain open for its virtual ports to be visible.

Network MIDI and cross-Mac routing

macOS supports MIDI over a local network through the built-in Network MIDI feature. This allows you to route MIDI between two Macs on the same network, or between a Mac and an iPhone or iPad running a compatible app. To set it up:

1. Open Audio MIDI Setup and go to Window > Show MIDI Studio
2. Double-click the Network icon in MIDI Studio
3. Check "Enable network MIDI" on both machines
4. On one machine, click the + button to add the other machine as a participant
5. Once connected, the remote Mac appears as a MIDI device in your DAW and in Midilize

Network MIDI adds approximately 10–30ms of additional latency depending on your network quality. It is suitable for monitoring remote MIDI sources or triggering sounds that are not time-critical, but not ideal for tight rhythmic performance. For zero-latency cross-Mac routing, a direct USB or Thunderbolt connection is preferred.

You can also monitor what flows through a Network MIDI port in Midilize: enable the network MIDI device in the Sources panel and any messages arriving over the network appear in Monitor Mode. This is useful for remotely diagnosing a MIDI setup on a second machine without physically being at that desk.

Merging and splitting MIDI streams

Two of the most powerful routing operations are merging (combining multiple sources into one destination) and splitting (sending one source to multiple destinations). Both are straightforward in Midilize's patch-graph:

Merging: Add multiple MIDI In nodes and connect all of them to a single MIDI Out node or processing tool. All messages from every source flow into the destination as a unified stream. This is how you combine a hardware keyboard and a software step sequencer into a single synthesizer input.

Splitting: Connect one MIDI In node to multiple MIDI Out nodes. Every incoming message is copied and forwarded to all destinations simultaneously. Add channel filters or note range filters on each output branch to send only specific messages to each destination — this is the foundation of keyboard splits and layered sounds.

Unlike the IAC driver, which delivers all data on a port to every subscriber without distinction, Midilize lets you apply different processing to each output branch independently. One branch can transpose, another can filter to specific channels, and a third can remap CC numbers — all from the same single input source.

Frequently asked questions