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.

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To sponsor this project visit https://github.com/sponsors/ExistentialAudio

Table of Contents

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

Features

• Builds 2, 16, 64, 128, and 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 additional driver latency
• Compatible with macOS 10.10 Yosemite and newer
• Builds for Intel and Apple Silicon
• No kernel extensions or modifications to system security necessary

Installation Instructions

Option 1: Download Installer

1. Download the latest installer
2. Close all running audio applications
3. Open and install package
4. Restart your system when prompted

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

• Download BlackHole 2ch Uninstaller
• Download BlackHole 16ch Uninstaller
• Download BlackHole 64ch Uninstaller

Option 2: Manually Uninstall

1. 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.

2. Restart CoreAudio with the terminal command:

   sudo killall -9 coreaudiod

For more specific details visit the Wiki.

User Guides

Logic Pro X

• Logic Pro X to FaceTime
• Logic Pro X to Google Meet
• Logic Pro X to Skype
• Logic Pro X to Zoom

GarageBand

• GarageBand to FaceTime
• GarageBand to Google Meet
• GarageBand to Skype
• GarageBand to Zoom

Audacity

• Audacity Setup

Reaper

• Reaper to Zoom by Noah Liebman

Record System Audio

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

Route Audio Between Applications

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

Developer Guides

A license is required for all non-GPLv3 projects

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

Build & Install

After building, to install BlackHole:

1. Copy or move the built BlackHoleXch.driver bundle to /Library/Audio/Plug-Ins/HAL
2. Restart CoreAudio using sudo killall -9 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 role 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 comma (,). For example: kSampleRates='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 the create_installer.sh shell script 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](https://github.com/ExistentialAudio/BlackHole/is