A Multi-Output Device sends one stream of audio out to several speakers at once. An Aggregate Device combines several microphones or interfaces so macOS treats their inputs as one device with more channels. One is for playback, the other is mainly for recording, and Audio MIDI Setup's near-identical naming is the main reason people confuse them.
Both live in the same + menu in Audio MIDI Setup, both combine several real devices into one, and both suffer from the same underlying problem. That is roughly where the similarity ends. Picking the wrong one for the job either does not work at all, or works in a way that looks fine until you notice the details are off.
What a Multi-Output Device actually does
A Multi-Output Device takes one stream of audio, whatever your Mac is currently playing, and hands an identical copy to every real output ticked inside it. Two speakers, a pair of Studio Displays, a soundbar and headphones, whatever you group, all of them play the same thing at the same moment. It is a fan-out: one source, several destinations, all hearing the same audio.
This is the one people reach for when the goal is "play this everywhere," and it is what covers cases like two Studio Displays sharing one output or any other setup where several speakers should all carry the same sound.
What an Aggregate Device actually does
An Aggregate Device works the other direction. Instead of fanning one signal out to many outputs, it combines several separate devices, usually microphones or audio interfaces, into what macOS sees as a single device with more input channels than any one of them has alone. Two two-channel interfaces become one four-channel device. Software that only understands "channels on one device" can suddenly use several physically separate microphones at once, recorded in sync with each other.
This is almost entirely a recording concept, not a playback one, and the audience for it is narrower: podcasters running several microphones through separate interfaces, musicians recording more inputs than one interface has ports for, and anyone whose recording software expects a single device rather than a scattered set of them.
Why do both share the same clock problem?
This is the part that trips people up on both, and it comes from the same root cause either way. Every audio device, whether it is a speaker or a microphone interface, runs on its own internal clock, and no two clocks run at exactly the same rate. Combine several of them, whether fanning audio out with a Multi-Output Device or pulling audio in with an Aggregate Device, and those tiny rate differences accumulate over time. On playback that shows up as one speaker slowly drifting out of sync with another. On recording it shows up as channels from different interfaces slipping out of phase with each other the longer a recording runs.
Both features offer the same fix in Audio MIDI Setup: pick one device as the primary, whose clock the others follow, and tick Drift Correction on every other device in the group. Wired connections hold together far better than Bluetooth, which adds its own delay on top of any clock drift and cannot be corrected away by this setting.
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Download for MacWhich one do you actually want?
| Multi-Output Device | Aggregate Device | |
|---|---|---|
| Direction | Fans one signal out to several outputs | Combines several inputs into one |
| Typical use | Play the same audio through multiple speakers | Record several microphones at once, in sync |
| Typical user | Anyone with more than one speaker | Podcasters, musicians, multi-mic recording |
| Suffers from clock drift | Yes | Yes |
| Volume of the group, natively | None, set devices individually | Not applicable, this is a recording feature |
If the question is "how do I get sound out of more than one speaker," you want a Multi-Output Device. If the question is "how do I record from more than one microphone or interface at the same time," you want an Aggregate Device. They solve different problems and neither one substitutes for the other.
Where Chorus fits, and where it does not
Chorus groups outputs the way a Multi-Output Device does, and adds a working volume for the group, which Audio MIDI Setup's own version does not have. That covers the playback side of this page: several speakers playing as one, with one control.
Chorus does not build Aggregate Devices or handle the multi-microphone recording use case. If you need several audio interfaces combined into one device for recording, that remains a job for Audio MIDI Setup directly, or for dedicated recording software built around that workflow. The two features named almost identically in Audio MIDI Setup solve genuinely different problems, and Chorus is built for one side of that, not both.
Frequently asked questions
What is the difference between a Multi-Output Device and an Aggregate Device on a Mac?
A Multi-Output Device fans one audio stream out to several speakers so they all play the same thing at once, mainly for playback. An Aggregate Device combines several microphones or interfaces into what macOS treats as one device with more input channels, mainly for recording several sources in sync.
Why do both a Multi-Output Device and an Aggregate Device have drift problems?
Every audio device runs on its own internal clock, and no two run at exactly the same rate. Combining several devices, whether fanning audio out for playback or pulling it in for recording, means those small rate differences build up over time unless one device is set as primary and the others use Drift Correction.
Can an Aggregate Device include outputs as well as inputs?
Technically yes, but almost everyone who creates one is solving a recording problem by combining inputs. The output side of the feature exists but goes largely unused in practice.
Which one do I want if I just want two speakers to play the same music?
A Multi-Output Device. It is built specifically for fanning one audio stream out to several outputs at once, which is the playback case, rather than the recording case an Aggregate Device is built for.
Does Chorus work with Aggregate Devices for multi-microphone recording?
No. Chorus groups outputs the way a Multi-Output Device does and adds a working volume for the group, covering the playback side of this comparison. Combining several interfaces for multi-microphone recording remains a job for Audio MIDI Setup or dedicated recording software.
