Why does my microphone volume keep changing on my Mac?

macOS lets any application write to the input gain of the default microphone through the CoreAudio property kAudioDevicePropertyVolumeScalar. Zoom's "Automatically adjust microphone volume", Discord's Automatic Gain Control and WebRTC apps in Chrome all use it, which is why your input slider moves on its own during calls.

Does macOS have a setting to lock the microphone input volume?

No. There is no setting in System Settings, Sound preferences or a supported defaults key that locks input volume. MicLock works around this by routing your microphone through an aggregate device, which exposes no volume control at all, so there is nothing for an application to write to.

How do I stop Zoom from changing my microphone volume?

In Zoom, open Settings, then Audio, and uncheck "Automatically adjust microphone volume". To stop every app at once, including ones with no such setting, run miclock lock, which removes the volume control from the device that apps see.

Does locking the microphone volume reduce audio quality?

No. The aggregate device passes the same audio stream through at the same sample rate. It removes a volume control rather than adding any processing.

Does MicLock work with USB microphones and Apple Silicon Macs?

Yes. MicLock works with the built-in microphone, USB microphones such as a Blue Yeti, audio interfaces and Bluetooth headsets, on both Apple Silicon (M1, M2, M3, M4) and Intel Macs running macOS 12 or later.

Does MicLock need microphone permission?

No. MicLock never opens an audio stream. It only reads and writes CoreAudio device properties, so macOS asks for no permission and MicLock has no access to your audio.

Stop apps from changing your microphone volume on macOS

MicLock freezes your Mac's microphone input volume so Zoom, Discord, Google Meet, Teams and Chrome can't move the slider mid-call. One command. No driver, no sudo.

curl -fsSL https://raw.githubusercontent.com/w1zardz/miclock/master/install.sh | bash
miclock lock --level 80

View on GitHub →

Why your mic volume keeps changing by itself

You set your input level in System Settings → Sound → Input. You join a call. Ten minutes later the slider sits at 3% and nobody can hear you — or it's pinned at 100% and clipping.

macOS lets any app write to the input gain of the default microphone, and several do it on every call without asking:

App	What it does to your mic
Zoom	"Automatically adjust microphone volume" is on by default and rewrites the system slider
Discord	Automatic Gain Control rides the input level
Google Meet, Chrome, any WebRTC site	WebRTC AGC adjusts hardware gain where the OS allows it
Microsoft Teams, Skype, Slack huddles	Automatic microphone level adjustment
OBS, Streamlabs, FaceTime, some drivers	Occasional level rewrites

macOS has no built-in setting to lock the input volume. That's the gap MicLock fills.

How MicLock locks it

1. Hard lock — a device with no volume control

miclock lock wraps your microphone in a private CoreAudio aggregate device and makes it the default input. Aggregate devices expose no volume control, so the property an app would write to simply doesn't exist. Not a policy an app can override — there's nothing to set.

$ miclock lock --level 80
✓ gain of "MacBook Pro Microphone" set to 80%
✓ locked — apps now see a device with no volume control

2. Watchdog — snap the level back

miclock watch installs a tiny LaunchAgent that restores your level within a second of anything moving it. Survives reboots, costs effectively nothing.

$ miclock watch --level 80
✓ watchdog running — snaps back to 80% within 2s, starts with your Mac

Run both for belt and braces: the lock stops apps changing the gain, the watchdog fixes the level if you ever unlock or swap headsets.

Install

curl -fsSL https://raw.githubusercontent.com/w1zardz/miclock/master/install.sh | bash

Needs the Xcode Command Line Tools (xcode-select --install) — the installer compiles a small Swift helper locally, so no unsigned binary is ever downloaded. Everything lives in your home directory, nothing runs as root, and miclock uninstall reverses all of it.

Commands

miclock lock [--level N]     Hard-lock the mic gain
miclock unlock               Undo the lock
miclock watch [--level N]    Background watchdog
miclock unwatch              Stop the watchdog
miclock status               What's locked and at what level
miclock devices              List input devices
miclock uninstall            Remove everything

Also switch off in-app AGC

MicLock freezes the hardware gain. Apps can still compress your voice in software, which sounds like the volume moving. Turn that off too:

Zoom → Settings → Audio → uncheck Automatically adjust microphone volume
Discord → Settings → Voice & Video → Automatic Gain Control off
Microsoft Teams → Settings → Devices → Automatically adjust mic sensitivity off
OBS → remove Gain / Compressor / Limiter filters on the mic source

FAQ

Why can apps change my microphone volume on a Mac at all?

CoreAudio exposes kAudioDevicePropertyVolumeScalar on input devices as writable to any process holding the device. No macOS permission gates it, so any app can set your mic gain.

Does macOS have a setting to lock the input volume?

No — not in System Settings, not via a supported defaults key. The aggregate device approach is the only way to make the gain genuinely unwritable without shipping a custom audio driver.

Does this reduce microphone quality?

No. The same stream passes through at the same sample rate. MicLock removes a volume control; it adds no processing.

USB mics, audio interfaces, Bluetooth headsets?

All work — anything that appears as an input device, including a Blue Yeti, Scarlett interface or the built-in mic, on Apple Silicon (M1–M4) and Intel.

Does it need microphone permission?

No. MicLock never opens an audio stream, only reads and writes device properties. macOS asks for nothing and MicLock has no access to your audio.

How do I undo it?

miclock unlock for the device, miclock unwatch for the watchdog, miclock uninstall for both plus the files.