The volume slider greys out because a Multi-Output Device is not really a device: it is a stack of two or more real outputs sharing one audio stream, and none of them owns the software slider your keyboard controls. macOS has nowhere to send a volume instruction, so it disables the control rather than guess.
This is not a bug, and it is not specific to one Mac, one macOS version, or one pair of speakers. It happens on every Multi-Output Device, every time, because of how the thing is built. Below is what is actually going on, the two free workarounds, why both of them are annoying in a different way, and the one paid fix that gives you a normal slider back.
What is a Multi-Output Device, really?
Open Audio MIDI Setup and a Multi-Output Device looks like any other item in the list, with its own name and its own icon. It is not one. It is a thin wrapper that macOS builds on the fly: pick two or three real outputs, tick them, and the wrapper sends the same audio to all of them at once. Nothing about the wrapper itself produces sound, holds a volume, or has hardware behind it.
A real speaker has one volume, set either by its own hardware or by a driver macOS talks to directly. A Multi-Output Device has none of that, because it is not a speaker. It is closer to a playlist of outputs than a device. That is the entire explanation for the greyed-out slider: macOS is not broken, it is being asked to change a value that does not exist.
The free workaround, and its real cost
Open Audio MIDI Setup, select the real device that is actually making the noise you want to change (not the Multi-Output Device itself), and drag its own Master slider. That is the whole trick: you are setting the real speaker's volume directly, because the wrapper has none of its own to set. Repeat for each device in the group, and switch back to Audio MIDI Setup every time you want to change the level.
The other common suggestion is to leave every device at full volume and control level inside whichever app is playing. That works fine for Spotify, Music, or a video player, all of which have their own on-screen slider. It stops working the moment anything else makes a sound. System alerts, Slack notifications, a Zoom ringtone, and any app with no volume control of its own all play at whatever level the hardware is fixed to, which with this workaround is maximum. The fix for one kind of loud problem quietly creates another.
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Download for MacHow does Chorus give the slider back?
Chorus groups your outputs the same way Audio MIDI Setup does, using the same multi-output support already built into macOS. The difference is what happens when you move the volume control: instead of trying to change a volume the group does not have, Chorus changes every real device's own level at the same time, in the same proportion. One slider, one keyboard shortcut, and the group moves together. The on-screen volume display you are used to seeing comes back too, because macOS is once again talking to devices that actually have a volume to report.
It also means the balance holds. Pull one side of a pair down to 70% because it sits closer to your desk, and that ratio stays fixed every time you use the group, rather than resetting the way a system-wide fix would.
Does this affect anything else?
A few knock-on symptoms come from the same root cause, and are worth knowing rather than treating as separate faults:
- Volume keys on the keyboard do nothing. They talk to the same missing slider, so they stop responding for exactly the same reason.
- The on-screen volume display does not appear. It has nothing to display, since there is no single number to show.
- Menu bar volume icon looks stuck at one level. It is showing the group's absence of a level, not a frozen reading.
- Third-party remotes and media keys stop controlling volume. Anything that relies on the system volume API hits the same dead end.
None of these are separate bugs to chase down individually. They are the same missing piece showing up in four places, and fixing the root cause fixes all four at once.
Frequently asked questions
Why does my Mac's volume slider grey out when I use a Multi-Output Device?
Because a Multi-Output Device is not a real device: it is a wrapper macOS builds to send one audio stream to several real outputs at once. None of those outputs shares a single volume with the group, so there is nothing for the slider or your volume keys to control, and macOS disables them rather than guess.
How do I change the volume with a Multi-Output Device selected?
Open Audio MIDI Setup, click the real device that is actually producing the sound you want to change (not the Multi-Output Device itself), and drag its own Master slider. You have to repeat this for each device in the group and switch back to Audio MIDI Setup every time.
Is a greyed-out volume slider a sign something is broken?
No. It happens on every Multi-Output Device, on every Mac, every time, because of how the feature is built rather than because of a fault. The same thing happens to Aggregate Devices on the input side, for the identical reason.
Does Chorus fix the greyed-out volume slider?
Yes. Chorus groups outputs the same way Audio MIDI Setup does, but when you move the volume control it changes every real device's own level at the same time, so one slider and your keyboard's volume keys work again for the whole group.
Why do my volume keys and on-screen volume display stop working too?
They rely on the same system volume that a Multi-Output Device does not have, so they fail for the same reason the slider greys out. Fixing the root cause, either by setting each device by hand or by using an app that sets them together, fixes all of these at once.
