disable-thru

macOS forgets the Thru setting on a USB audio input device. Thru routes the device's input straight back to its own output, so you hear yourself. If you do not want that, you turn it off in Audio MIDI Setup, and macOS turns it back on at the next restart.

This is not a bug in your settings. The Thru state lives on the CoreAudio device object, which macOS rebuilds from the driver default every time the device appears: at every restart, and at every replug. Audio MIDI Setup writes the setting to that object, so the rebuild takes it with it.

This program sets Thru off again, and a launch agent runs the program each time the setting would otherwise come back.

Written for a Blue Yeti, but it works with any input device that exposes a Thru setting.

Requirements

• macOS. The program uses CoreAudio, and the launch agent uses launchd.
• The Command Line Tools, which supply the Swift compiler. Check with swiftc --version. If that fails, run xcode-select --install.
• just, for the recipes below.
• fzf is optional. The device picker uses it when present, and falls back to a numbered menu otherwise.

Tested on macOS 26. The CoreAudio and launchd interfaces are long established, so earlier versions should also work.

Quick start

git clone https://github.com/mapitman/disable-thru.git
cd disable-thru
just configure
just install

just configure builds the program, asks which device to target, and writes a launch agent for it. just install loads that agent.

Then confirm it worked. Turn Thru on in Audio MIDI Setup, unplug the device, plug it back in, and wait about ten seconds. Thru should switch itself off.

The recipes

Run just with no arguments to list them.

Recipe	What it does
just build	Compiles the program to ~/.local/bin/disable-thru.
just list	Lists the input devices that expose a Thru setting.
just pick	Turns Thru off now, on a device you pick from a list.
just configure	Picks a device and writes the launch agent for it.
just configure-for "<name>"	The same, without the picker.
just install	Loads the launch agent.
just status	Shows whether the agent is registered, and its last exit status.
just uninstall	Unloads and removes the agent.
just clean	Deletes the compiled program.
just ids "<usb-name>"	Prints a USB device's vendor and product IDs.
just usb	Lists every USB device with its IDs.

Using the program directly

just build puts the program in ~/.local/bin. The examples below assume that directory is on your PATH; if it is not, call it by its full path instead.

The program takes a device name, matched as a prefix:

disable-thru "Yeti Stereo Microphone"

It reports which device it changed, including the CoreAudio device ID:

Thru disabled: Yeti Stereo Microphone [id 114]

That ID is assigned by CoreAudio and changes between restarts and replugs, so expect a different number. The program matches on the name for that reason.

To see the devices it can act on:

disable-thru --list

The list holds only devices that have input channels and expose a Thru setting, so most audio devices do not appear.

Why a launch agent

launchd starts the agent with no terminal attached, and it fires on both of the events this program cares about:

• RunAtLoad covers logging in.
• A LaunchEvents block with com.apple.iokit.matching covers the device being plugged in.

On the second trigger the agent retries for up to ten seconds, because the USB device attaches a moment before CoreAudio finishes registering it.

How the configuration works

dist/local.disable-thru.plist.template holds three placeholders, which just configure fills in:

Placeholder	Filled with
__DEVICE_NAME__	The device you chose.
__ID_VENDOR__	Its USB vendor ID, in decimal.
__ID_PRODUCT__	Its USB product ID, in decimal.

just configure reads the USB IDs from the IOAudioDeviceModelID property in the I/O registry, which holds them in the form <name>:<vendor>:<product>. That is an exact link from the audio device to its USB identity, so the IDs are never guessed from the device names, which do not match: a Blue Yeti reports as Yeti Stereo Microphone to CoreAudio and as Blue Microphones over USB.

The generated dist/local.disable-thru.plist is ignored by git, because it is specific to one machine's hardware. Re-run just configure after changing device, then just install.

Troubleshooting

Run the program by hand first:

just build
~/.local/bin/disable-thru --list

If your device is not listed, it has no Thru setting that CoreAudio exposes, and no launch agent will change that.

To make the agent run immediately, without unplugging anything:

launchctl kickstart -k gui/$(id -u)/local.disable-thru
tail -5 ~/Library/Logs/disable-thru.log

For a wider view, read the system log:

log show --predicate 'eventMessage CONTAINS "disable-thru"' --last 10m

If logging in works but plugging the device in does not, the USB IDs in the generated plist are probably wrong. Re-run just configure with the device connected.

Note that system_profiler SPUSBDataType shows USB details in a friendlier layout than ioreg, but it returns nothing in some environments. The recipes use ioreg for that reason.

A caveat

IOMatchLaunchStream, the key that makes the plug-in trigger work, is not documented by Apple. It is widely used and it works, but Apple could change it. If it ever stops working, replace the whole LaunchEvents block in the template with a timed check, which is documented and dependable but slower to react:

<key>StartInterval</key>
<integer>30</integer>

How it works

The program asks CoreAudio for every audio device, keeps the ones whose name starts with the name you gave, and then keeps only those with input channels. That last filter matters: macOS splits a Yeti into two devices that share one name, an input and an output, and only the input carries the Thru control.

On the matching device it sets kAudioDevicePropertyPlayThru to zero.

License

MIT. See LICENSE.