In short
Open Audio MIDI Setup, click Add (+) at the bottom of the sidebar and choose Create Aggregate Device. Tick Use for each device, pick the most reliable Clock Source, and turn on Drift Correction for the others. To play through several outputs at once, choose Create Multi-Output Device.
To create an aggregate device on a Mac, open Audio MIDI Setup, click the Add button (+) at the bottom of the sidebar, and choose Create Aggregate Device. Tick Use for each device you want to combine, choose the most reliable one as the Clock Source, and turn on Drift Correction for the others. To play the same sound through several outputs at once, choose Create Multi-Output Device instead.
This guide covers both, step by step, and what each one is for. The steps and menu names were checked against Apple's Audio MIDI Setup User Guide and Audio MIDI Setup on macOS 26.6 on 25 September 2026.
Create an aggregate device
- Open Audio MIDI Setup. It is in Applications › Utilities, or in the Finder choose Go › Utilities.
- Show the audio devices. If you see the MIDI window instead, choose Window › Show Audio Devices.
- Connect every device first. Apple recommends connecting external audio interfaces before you begin.
- Add the aggregate device. Click + at the bottom of the sidebar and choose Create Aggregate Device. A new device called "Aggregate Device" appears in the sidebar.
- Name it. Click its name in the sidebar and type something you will recognise, such as "Mic + interface".
- Tick the devices to include. With the new device selected, tick Use beside each device you want in it.
- Choose the clock source. From the Clock Source menu, choose the device with the most reliable clock, usually your main audio interface.
- Turn on drift correction. Tick Drift Correction for every device that is not the clock source.
- Check the sample rate. Apple says all devices in an aggregate device should use the same sample rate. Set it in the Sample Rate menu.
- Select it in your app. Choose the aggregate device as the input or output in the app that needs it.
To remove it later, select it in the sidebar and click −.
What an aggregate device is for
Apple describes an aggregate device as a way to make multiple devices appear as a single device in an app, to increase the number of inputs and outputs available at the same time. Apple's own examples are music apps such as Logic Pro, GarageBand and MainStage, and other Core Audio apps.
For calls and recording, it comes up in a few situations:
- Two microphones into an app that takes one input, for example two people in a room each with their own microphone.
- A microphone plus a loopback driver, so an app that records one input gets both your voice and the Mac's sound. Record your microphone and Mac audio at the same time compares this with the alternatives.
- Extra channels from two interfaces used as one.
An aggregate device presents all its channels at once. What the app does with them varies: a multitrack editor can put each on its own track; a simple recorder may take the first two channels, or mix them, or miss one entirely. Test before relying on it.
Create a multi-output device
A multi-output device sends the same sound to several outputs at once. The usual reason on a call is to keep hearing the call in your headphones while also sending it to something else, such as a loopback driver a recorder listens to.
- Open Audio MIDI Setup and show the audio devices.
- Add the device. Click + at the bottom of the sidebar and choose Create Multi-Output Device.
- Tick the outputs. Tick Use beside each output you want, such as your headphones and the loopback driver.
- Choose the primary device. From the Primary Device menu, choose the output whose clock the others follow, usually your headphones or interface.
- Turn on drift correction for the devices that are not primary.
- Send your sound to it. In System Settings › Sound › Output, choose the multi-output device.
Apple's description: audio sent to the primary device also plays through any other device in the stack.
Aggregate or multi-output
| You want | Use |
|---|---|
| Two inputs to appear as one input | Aggregate device |
| More channels from two interfaces | Aggregate device |
| The same sound in headphones and somewhere else | Multi-output device |
| An app to record both your voice and the Mac's sound | Both, plus a loopback driver, or a recorder that does it by itself |
Problems and fixes
- Clicks, crackles or a slow drift out of sync. The devices' clocks disagree. Set the clock source to the most reliable device and turn on drift correction for the rest. Apple notes one exception: if your devices share a separate word clock connection, turn drift correction off and follow the device maker's instructions.
- No sound from one device. Check its Use box is ticked, and that the app is set to the aggregate device, not to one of its members.
- It stopped working after a device was unplugged. An aggregate device needs its members connected. Reconnect the device, or rebuild the aggregate with the devices you now have.
- Bluetooth headphones behave oddly in a multi-output device. Bluetooth adds its own delay and switches mode when its microphone opens, so it is the least predictable member. Wired headphones are easier.
- The call app changed device. Some call apps choose their own input and output and can switch away from the ones you built. Set them explicitly in the call app too.
A setup like this is easy to leave half-configured. The most common failure is output still set to the multi-output device after the call, or the recorder still pointed at the aggregate after a headset changed. Write down what you set, and set it back.
Recording system audio needs more than this
Neither device, on its own, turns what the Mac plays into something an app can record. That needs a loopback driver, a virtual device that presents the Mac's output as an input. Recording your Mac's system audio covers the options.
On macOS 26, Audio MIDI Setup also lists Create Audio Tap… in the same menu. That is part of Apple's newer way of capturing audio from apps, which recorders can use directly.
When you do not need either
A two-track recorder that captures your microphone and what the Mac plays by itself needs neither device. Notey records the input selected in System Settings as one track and what the Mac plays as the other, using a Core Audio process tap, on Macs with Apple silicon running macOS 26 or later. There is nothing to build in Audio MIDI Setup and nothing to set back afterwards. Setting up your Mac's audio for calls covers the settings that still matter, of which headphones are the most important: on speakers, the other side ends up on your track.
Frequently asked questions
What is an aggregate device on a Mac?
A virtual audio device, made in Audio MIDI Setup, that combines several real devices into one. Apps see a single device with all their inputs and outputs, so an app that can only choose one input can use two microphones at once.
What is the difference between an aggregate device and a multi-output device?
An aggregate device combines devices' inputs and outputs into one device with more channels. A multi-output device plays the same sound through several outputs at the same time, such as headphones and a recorder's input.
Why does my aggregate device crackle or drift out of sync?
Separate devices keep slightly different time. Choose the device with the most reliable clock as the Clock Source and turn on Drift Correction for every other device. Apple also says all devices should use the same sample rate.
Do I need an aggregate device to record a call on a Mac?
Not with a recorder that captures your microphone and what the Mac plays by itself. Aggregate devices are one way to do it with apps that can only record one input.
How do I delete an aggregate device?
In Audio MIDI Setup, select it in the sidebar and click Remove (the minus button) at the bottom.