Slack, at the volume
of an emergency.

Slack is unusually good at being the loudest thing on a Mac, and unusually confusing to fix, because the noises it makes do not all come from the same place. Get that distinction right and the rest is quick.

The distinction that matters

Two different systems are producing "Slack sounds" on your Mac:

• Audio Slack plays itself — huddle audio, calls, screen-share audio, and the in-app sounds it generates while you are looking at it. This is Slack producing sound as an application.
• Notification sounds delivered by macOS — the chime attached to a banner when someone messages you while Slack is in the background. On macOS 12 and later these are handled by the system notification path, which is why they behave differently and why they are not governed by an app volume control.

Almost every failed attempt to quieten Slack is someone applying the fix for one of these to the other.

Fixing the notification side (macOS)

1. System Settings → Sound → Alert volume. A separate slider from your output level, and the single most useful control here. Pull it to a third and every system alert stops being startling, without touching music, calls or video.
2. System Settings → Notifications → Slack. Turn off Play sound for notifications and keep the banners. You still see the message, you just do not get announced.
3. Slack → Preferences → Notifications. Under Sound & appearance you can choose a different notification sound and, separately, the huddle notification sound. A gentler sound is often enough on its own.
4. A Focus mode. Stops banners and their sounds entirely for as long as it is on, and can be triggered by a schedule or by sharing your screen.

Fixing the huddle side

Huddle audio is Slack playing sound like any other app, so:

• Slack's own audio settings let you set the input and output device used for huddles independently of the rest of your system. Worth setting explicitly if you use headphones for calls and speakers for everything else.
• A per-app fader controls it directly. This is what you want when huddles are consistently louder than your music or your Zoom calls — a level that belongs to Slack alone and stays where you put it.

The general fix: give Slack its own fader

Everything above is Slack fixing Slack. The reason you keep running into this is more basic: macOS has exactly one volume, and it moves everything at once. Windows has had a per-application volume mixer since 2007. macOS never shipped one, and it is not an oversight Apple is quietly working on — it is a consequence of how Core Audio was built.

What changed is that in 2024 Apple shipped Core Audio process taps as a public API, which lets a signed app capture and adjust the audio of one specific process in user space. No virtual audio driver, no kernel extension, no restart, and no swapping your default output device for a fake one. That is what MixPill is built on, and it is why the setup is a single macOS permission rather than an installer and a reboot. The longer version is in why macOS has no volume mixer.

In practice: every app currently making sound gets a row with a fader, a mute, a solo and a live dBFS meter. Set Slack to 40% and leave everything else alone. The level belongs to Slack and persists, so you set it once. Unity sits at 80% of the fader travel with up to +6 dB above it, so an app that is too quiet can be pushed up rather than only down — which is half the reason people go looking for a mixer in the first place.

All of that is free, for unlimited apps, permanently — no trial clock and no nag screens. Pro adds per-app EQ and a noise gate, per-app output routing, presets, and Auto-Ducking that drops everything else to 20% whenever a call takes hold of an audio input.

Being straight about the limits

A per-app mixer controls what an application plays. A notification sound that macOS plays on Slack's behalf is coming from the system, not from Slack's audio path, so it is not something an app fader is the right tool for — the Alert volume slider and the per-app notification sound toggle are. That is not a limitation anyone can engineer around; it is where macOS draws the line, and knowing where it is saves you twenty minutes of moving the wrong slider.

The half that is in scope — huddles, calls, everything Slack plays itself — is exactly what a fader per app is for, and it is free.

The setup worth having if huddles are constant

If you get pulled into unscheduled huddles all day, the useful configuration is not a level at all — it is ducking. With Auto-Ducking on, the moment any app takes hold of an audio input, everything else drops to 20% and comes back when the call ends. A huddle starting is exactly that event, so music gets out of the way without you doing anything. How that works, and the alternative if you want a trigger you control by hand.

Common questions