BlackHole: Audio Loopback Driver

BlackHole is a modern macOS virtual audio loopback driver that allows applications to pass audio to other applications with zero additional latency.

Funding

Sponsor: https://github.com/sponsors/ExistentialAudio

Features
Installation Instructions
Uninstallation Instructions
User Guides
Developer Guides
Feature Requests
FAQ
Wiki

Features

Builds 2, 16, 64, 128, 256 audio channels versions
Customizable channel count, latency, hidden devices
Customizable mirror device to allow for a hidden input or output
Supports 8kHz, 16kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz, 192kHz, 352.8kHz, 384kHz, 705.6kHz and 768kHz sample rates
Zero driver latency
Compatible with macOS Yosemite (10.10) and newer.
Builds for Intel and Apple Silicon

Installation Instructions

Option 1: Download Installer

Download the latest installer
Close all running audio applications
Open and install package

Option 2: Install via Homebrew

2ch: brew install blackhole-2ch
16ch: brew install blackhole-16ch
64ch: brew install blackhole-64ch

Uninstallation Instructions

Option 1: Use Uninstaller

Option 2: Manually Uninstall

Delete the BlackHole driver with the terminal command:

rm -R /Library/Audio/Plug-Ins/HAL/BlackHoleXch.driver

Be sure to replace X with either 2, 16, or 64.

Note that the directory is the root /Library not /Users/user/Library.
Restart CoreAudio with the terminal command:

sudo launchctl kickstart -kp system/com.apple.audio.coreaudiod

For more specific details visit the Wiki.

User Guides

Logic Pro X

GarageBand

Reaper

Reaper to Zoom by Noah Liebman

Record System Audio

Setup Multi-Output Device
In Audio Midi Setup → Audio Devices right-click on the newly created Multi-Output and select "Use This Device For Sound Output"
Open digital audio workstation (DAW) such as GarageBand and set input device to "BlackHole"
Set track to input from channel 1-2
Play audio from another application and monitor or record in your DAW

Route Audio Between Applications

Set output driver to "BlackHole" in sending application
Output audio to any channel
Open receiving application and set input device to "BlackHole"
Input audio from the corresponding output channels

Developer Guides

A license is required for all non GPL-3.0 projects.

Please support our hard work and continued development. To request a license contact Existential Audio.

Installation

To install BlackHole copy the BlackHoleXch.driver folder to /Library/Audio/Plug-Ins/HAL and restart CoreAudio using sudo launchctl kickstart -kp system/com.apple.audio.coreaudiod.

Customizing BlackHole

The following pre-compiler constants may be used to easily customize a build of BlackHole.

kDriver_Name
kPlugIn_BundleID
kPlugIn_Icon

kDevice_Name
kDevice_IsHidden
kDevice_HasInput
kDevice_HasOutput

kDevice2_Name
kDevice2_IsHidden
kDevice2_HasInput
kDevice2_HasOutput

kLatency_Frame_Size
kNumber_Of_Channels
kSampleRates

They can be specified at build time with xcodebuild using GCC_PREPROCESSOR_DEFINITIONS.

Example.

xcodebuild \
-project BlackHole.xcodeproj \
GCC_PREPROCESSOR_DEFINITIONS='$GCC_PREPROCESSOR_DEFINITIONS 
kSomeConstant=value'

Be sure to escape any quotation marks when using strings.

Renaming BlackHole

To customize BlackHole it is required to change the following constants.

kDriver_Name
kPlugIn_BundleID (note that this must match the target bundleID)
kPlugIn_Icon

These can specified as pre-compiler constants using xcodebuild.

driverName = "BlackHole"
bundleID = "audio.existential.BlackHole"
icon = "BlackHole.icns"

xcodebuild \
-project BlackHole.xcodeproj \
-configuration Release \
PRODUCT_BUNDLE_IDENTIFIER=$bundleID \
GCC_PREPROCESSOR_DEFINITIONS='$GCC_PREPROCESSOR_DEFINITIONS
kDriver_Name=\"'$driverName'\"
kPlugIn_BundleID=\"'$bundleID'\"
kPlugIn_Icon=\"'$icon'\"'

Customizing Channels, Latency, and Sample Rates

kNumber_Of_Channels is used to set the number of channels. Be careful when specifying high channel counts. Although BlackHole is designed to be extremely efficient at higher channel counts it's possible that your computer might not be able to keep up. Sample rates play a roll as well. Don't use high sample rates with a high number of channels. Some applications don't know how to handle high channel counts. Proceed with caution.

kLatency_Frame_Size is how much time in frames that the driver has to process incoming and outgoing audio. It can be used to delay the audio inside of BlackHole up to a maximum of 65536 frames. This may be helpful if using BlackHole with a high channel count.

kSampleRates set the sample rate or sample rates of the audio device. If using multiple sample rates separate each with a ,. Example: 44100, 48000.

Mirror Device

By default BlackHole has a hidden mirrored audio device. The devices may be customized using the following constants.

// Original Device
kDevice_IsHidden
kDevice_HasInput
kDevice_HasOutput

// Mirrored Device
kDevice2_IsHidden
kDevice2_HasInput
kDevice2_HasOutput

When all are set to true a 2nd BlackHole will show up that works exactly the same. The inputs and outputs are mirrored so the outputs from both devices go to the inputs of both devices.

This is useful if you need a separate device for input and output.

Example

// Original Device
kDevice_IsHidden=false
kDevice_HasInput=true
kDevice_HasOutput= false

// Mirrored Device
kDevice2_IsHidden=false
kDevice2_HasInput= false
kDevice2_HasOutput=true

In this situation we have two BlackHole devices. One will have inputs only and the other will have outputs only.

One way to use this in projects is to hide the mirrored device and use it behind the scenes. That way the user will see an input only device while routing audio through to the output behind them scenes.

Hidden audio devices can be accessed using kAudioHardwarePropertyTranslateUIDToDevice.

Continuous Integration / Continuous Deployment

BlackHole can be integrated into your CI/CD. Take a look at https://github.com/ExistentialAudio/BlackHole/blob/master/Installer/create_installer.sh to see how the installer is built, signed and notarized.

Feature Requests

If you are interested in any of the following features please leave a comment in the linked issue. To request a features not listed please create a new issue.

Sync Clock with other Audio Devices in development see v0.3.0
Output Blackhole to other Audio Device
Add Support for AU Plug-ins
Inter-channel routing
Record Directly to File
Configuration Options Menu
Support for Additional Bit Depths

FAQ

Why isn't BlackHole showing up in the Applications folder?

BlackHole is a virtual audio loopback driver. It only shows up in Audio MIDI Setup, Sound Preferences, or other audio applications.

How can I listen to the audio and use BlackHole at the same time?

Setup a Multi-Output Device.

How can I change the volume of a Multi-Output device?

Unfortunately macOS does not support changing the volume of a Multi-Output device but you can set the volume of individual devices in Audio MIDI Setup.

Why is nothing playing through BlackHole?

Check System Preferences -> Security & Privacy -> Privacy -> Microphone to make sure your digital audio workstation (DAW) has microphone access.
Check that the volume is all the way up on BlackHole input and output in Audio Midi Setup.
If you are using a multi-output device, due to issues with macOS the Built-in Output must be enabled and listed as the top device in the Multi-Output. See here for details.

Why is audio glitching after X minutes when using a multi-output or an aggregate?

You need to enable drift correction for all devices except the Clock Source also known as Master Device or Primary Device.

Why is the Installer failing?

Check to make sure "Installer" has File and Folder permission and Full Disk Access in System Settings->Privacy and Security.

What Apps Don't Work with Multi-Outputs?

Unfortunately multi-outputs are pretty buggy and some apps just won't work with them at all. Here is a list of known ones. If you have more to add please let me know.

Apple Podcasts
Apple Messages
HDHomeRun

AirPods with an Aggregate/Multi-Output is not working.

The microphone from AirPods runs at a lower sample rate which means it should not be used as the primary/clock device in an Aggregate or Multi-Output device. The solution is to use your built-in speakers (and just mute them) or BlackHole 2ch as the primary/clock device. BlackHole 16ch will not work as the primary since the primary needs to have 2ch.

Read the discussion. ExistentialAudio#146

Can I integrate BlackHole into my app?

BlackHole is licensed under GPL-3.0. You can use BlackHole as long as your app is also licensed as GPL-3.0. For all other applications please contact Existential Audio directly.

ForrestSu / BlackHole