How to Create and Configure an Aggregate Audio Device in Audio MIDI Setup on Mac

Modern recording, podcasting, live streaming, and music production workflows frequently require simultaneous recording from multiple distinct audio interfaces or USB microphones. However, most digital audio workstations (DAWs) and desktop recording applications—including GarageBand, Logic Pro, Audacity, and OBS Studio—only permit selecting a single audio input device within their operational preferences. In macOS, Apple solves this architectural constraint natively through Aggregate Devices in the built-in Audio MIDI Setup utility.

An Aggregate Device combines multiple physical audio inputs and outputs into a single virtual master interface. The operating system coordinates clock synchronization, drift correction, and channel mapping behind the scenes, allowing your applications to record from multiple hardware sources simultaneously without latency or hardware clock collisions. This comprehensive tutorial details how to create, configure, and optimize an Aggregate Device on macOS.

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Aggregate Device vs Multi-Output Device: Understanding the Difference

macOS Audio MIDI Setup offers two distinct virtual audio configurations that serve different recording and playback scenarios:

• Aggregate Device: Combines multiple independent audio input and output devices into one unified virtual interface. This allows you to record from two separate USB microphones or multiple USB sound cards simultaneously while preserving discrete channels for each physical source.
• Multi-Output Device: Routes a single stereo or surround audio playback stream simultaneously to multiple physical output destinations (such as headphones and external studio monitors) without combining input streams.

If your primary objective is recording multi-source speech or instruments across multiple hardware interfaces simultaneously, an Aggregate Device is the correct configuration.

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Step 1: Connecting Hardware and Opening Audio MIDI Setup

Before launching macOS Audio MIDI Setup, connect all relevant hardware to ensure the system recognizes the devices:

1. Connect all your USB microphones, external audio interfaces, or digital mixers directly to your Mac. Wherever possible, avoid unpowered passive USB hubs, as bandwidth contention can cause dropped audio packets.
2. Launch Audio MIDI Setup using either of the following methods:
   • Press Command + Space to open Spotlight, type Audio MIDI Setup, and press Return.
   • Open Finder, navigate to Applications > Utilities, and double-click Audio MIDI Setup.
3. If the audio window does not display immediately, select Window > Show Audio Devices from the menu bar (or press Command + 1).

The left-hand sidebar displays all currently recognized input and output hardware, including built-in microphones, built-in speakers, and connected USB devices.

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Step 2: Creating a New Aggregate Device

Follow these steps to generate the virtual aggregate container:

1. Click the Add (+) button located at the bottom-left corner of the Audio Devices window.
2. From the pop-up contextual menu, select Create Aggregate Device.
3. A new entry named “Aggregate Device” appears in the sidebar list.
4. Double-click the new device’s name or press Return to rename it descriptively (e.g., Podcasting Duo, Studio Mic Array, or Dual Interface Setup).

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Step 3: Selecting and Ordering Your Hardware Interfaces

With the newly created Aggregate Device selected in the sidebar, the right-hand panel reveals the configuration matrix displaying all available audio hardware.

1. In the Use column of the device table, tick the checkbox adjacent to each hardware device you wish to include in the aggregate group. For example, select Blue Yeti Microphone and Scarlett 2i2 USB.
2. Inspect the Subdevices summary bar at the top of the panel. The color-coded blocks illustrate the exact channel order allocated to each physical device.
3. To reorganize channel ordering (e.g., ensuring Mic 1 occupies input channels 1–2 and Mic 2 occupies channels 3–4), drag the individual device blocks left or right within the Subdevices bar.

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Step 4: Configuring Clock Source and Drift Correction

Because multiple independent USB audio devices possess their own internal hardware clock crystals, subtle variations in timing will inevitably cause digital clicks, pops, or audio drift over extended recording sessions. Configuring master clocking and drift correction is critical for clean audio.

Selecting the Master Clock Source

From the Clock Source drop-down menu near the top of the panel, select your highest-quality hardware interface (for example, your primary dedicated audio interface rather than a basic USB microphone or built-in Mac audio). This device serves as the authoritative timing clock for all aggregated streams.

Enabling Drift Correction

In the device table below, observe the Drift Correction column:

• The device designated as the Clock Source will have its Drift Correction box automatically greyed out.
• For all other secondary devices in the list, ensure the Drift Correction checkbox is ticked.

Drift Correction activates an intelligent macOS resampler that dynamically compensates for micro-variations between hardware clocks in real time, preventing phase misalignment and synchronization errors.

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Step 5: Verifying Sample Rate Uniformity

To avoid hardware resampling artefacts, ensure all participating physical devices operate at an identical sample rate:

1. In the Format drop-down menu of the Aggregate Device, select your standard project sample rate (typically 44.1 kHz for standard speech/music or 48.0 kHz for video production and streaming).
2. In the left-hand sidebar, click on each physical child device individually and verify that its input format matches the chosen sample rate (e.g., 2 ch 24-bit Integer 48.0 kHz).

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Step 6: Routing the Aggregate Device in Your DAW or Recording Software

Once configured, the Aggregate Device behaves exactly like a native physical hardware audio interface across all macOS applications.

Using the Aggregate Device in GarageBand or Logic Pro

1. Launch GarageBand or Logic Pro.
2. Navigate to Settings (or Preferences) > Audio.
3. Set the Input Device to your newly named Aggregate Device (e.g., Podcasting Duo). Set the Output Device to your preferred listening headphones or system speakers.
4. Apply changes. When creating audio tracks in your DAW project, assign Input 1 to Track 1, Input 2 to Track 2, Input 3 to Track 3, and so forth, according to the subdevice channel layout configured in Step 3.

Using the Aggregate Device in Audacity

1. Open Audacity > Preferences > Audio Settings.
2. Set the Recording Device to your Aggregate Device.
3. Set Channels to match the total count of active inputs (e.g., 4 (Stereo/Quad) or individual mono tracks).

Using the Aggregate Device in OBS Studio

1. Open OBS Studio > Settings > Audio.
2. Under Global Audio Devices, assign Mic/Auxiliary Audio to your Aggregate Device.
3. Open the Advanced Audio Properties in OBS to balance individual channel levels or downmix to mono if capturing independent dialogue mics.

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Troubleshooting Aggregate Audio Configuration

Symptom	Probable Cause	Recommended Resolution
Audio clicks, pops, or crackling	Clock synchronization conflict	Verify that Drift Correction is enabled for all secondary subdevices except the designated Clock Source.
Muffled or robotic audio quality	Sample rate mismatch	Ensure all member devices and your DAW project settings share the exact same sample rate (44.1 kHz or 48.0 kHz).
One microphone drops out completely	USB bus bandwidth exhaustion	Connect devices to separate physical USB buses (e.g., opposite sides of your MacBook) or use a mains-powered USB hub.
Device missing in DAW menu	macOS Microphone permission blocked	Navigate to System Settings > Privacy & Security > Microphone and ensure your DAW has permission enabled.