How to Create an Aggregate Device in Audio MIDI Setup

Before you start

An aggregate device lets you combine two or more physical audio devices into one virtual device that apps can use as a single input device or output device. This is useful when you want to record several USB microphones at once, send audio to multiple interfaces, or join separate input and output hardware into one selection.

This process runs locally on your Mac. It does not require an online service or a new driver. You need at least two audio devices connected and recognized by macOS, plus an administrator account if macOS asks for permission changes. The tools involved are available through the built-in Audio MIDI Setup application.

Before making changes, close apps that are actively using the audio devices. This avoids sample rate conflicts and prevents an app from keeping the old device selection after you create the new virtual device.

Step-by-step instructions

Open Audio MIDI Setup. You can find it in the Utilities folder inside Applications, or open Spotlight and search for Audio MIDI Setup.

Show the audio device list. If you do not see the Audio Devices window, choose Show Audio Devices from the Window menu.

Create the aggregate device. Click the plus button near the bottom-left corner of the Audio Devices window and choose Create Aggregate Device.

Rename the new device. An aggregate device appears with a default name. Select it and enter a name that makes its role clear, such as Interview Mics or Streaming Output.

Select the included devices. With the aggregate device selected, look for the list of available audio hardware on the right. Enable the checkbox for each sound device that should belong to the aggregate device.

Arrange the channels. Use the subdevice list to drag devices into the order that should define the channel layout. The first enabled device supplies the initial channels, followed by the next enabled device.

Set the clock source. If a physical device offers clock source options, choose the device most likely to stay connected during the session. In many setups, the default clock source is sufficient, but a dedicated audio interface may be more stable than a USB webcam as the master clock.

Confirm the sample rate. The aggregate device shows a format section with available sample rates. Set the same sample rate that your recording or conferencing app expects, such as 44,100 Hz or 48,000 Hz. All included devices should support the selected rate.

Your change is reversible. You can disable a device from the aggregate or delete the aggregate device later without removing any physical hardware. The original devices remain available individually in app settings.

Check the output

Select the aggregate device as the input device or output device in the app you plan to use. In many video call and recording applications, the device choice appears in the audio settings or preferences.

Play or record a short local test. Speak into each microphone while watching the in-app meter, or play audio and confirm that all intended output devices are active. Listen for dropouts, echo, or channels that remain silent.

Check the input level in Audio MIDI Setup or the host app if it provides a meter. A healthy signal should move the meter without staying at maximum. If one source is much quieter, adjust its physical gain or app level rather than relying on the aggregate device to balance levels.

An aggregate device does not change the underlying hardware format. Some devices expose only fixed sample rates or channel counts, and the aggregate may then be limited by the least flexible member.

Common problems and next steps

If the app does not show the new device, quit and reopen the app after creating the aggregate. Some applications read the macOS audio device list only at launch.

If you hear clicks, pops, or audio that drifts out of sync, the clock source is a likely cause. Choose one physical device as the clock source, then make sure that device stays connected and powered on.

If an included device disappears, check its USB connection, hub, or power source. A disconnected subdevice can stop the whole aggregate from working because the virtual device expects all of its members to be present.

If the sample rate is grayed out or keeps changing, close apps that may be forcing their own format. Then select the aggregate device and set the sample rate before opening the recording or conferencing app.

For noisy recordings, first reduce background noise at the source: move the microphone closer, lower the gain, and reduce room noise. If the app offers noise reduction, apply it there because level and processing controls usually belong to the host app rather than to the aggregate device itself.