BlackHole passes audio between Mac applications. With a Multi-Output Device, your music player can send its sound to both your headphones and BlackHole; BUTT captures BlackHole and broadcasts it to VosCast.
This setup sends application audio. BlackHole is an audio driver, not a mixer, so these steps do not combine a microphone with your music.
Get ready
Install BlackHole 2ch from Existential Audio and install BUTT. Use the two-channel driver for this walkthrough. Follow the installer's instructions, then confirm BlackHole 2ch appears in Audio MIDI Setup.
Connect wired headphones or a suitable USB audio interface. Keep your Mac, audio player, and BUTT running throughout the broadcast.
Open Overview → Live broadcasting in your VosCast account. Stop hosted Auto DJ before connecting directly, and disconnect another live encoder if one is using the station.
Create a Multi-Output Device
- Open Audio MIDI Setup using Spotlight. If necessary, choose Window → Show Audio Devices.
- Check the sample rate of BlackHole 2ch and your headphone output in their Format settings. Use a rate supported by both, such as 48,000 Hz or 44,100 Hz.
- Click + at the bottom of the device list and choose Create Multi-Output Device.
- Enable Use for your two-channel headphone output and BlackHole 2ch. Rename the device something recognisable, such as Radio playback.
- Choose the headphone output as Primary Device or Clock Source, depending on the macOS version. Enable Drift Correction for BlackHole, leaving it off for the primary device.
The Multi-Output Device sends the same programme to both destinations. Your headphones provide local listening; BlackHole provides the signal for BUTT.
Send your player's output to it
In System Settings → Sound → Output, select the Multi-Output Device you just created. Start playback and confirm that you hear it in your headphones. If an application has its own output selector, set it to this device or to the system default.
Changing the system output also routes other sounds using that output, including alerts and browser audio. Close unwanted applications and silence audible notifications before broadcasting. Do not cue or preview another track through this same output: that audio will also reach BlackHole.
The normal Mac volume keys may not control a Multi-Output Device. Set a comfortable headphone level using the physical device's control or its individual level in Audio MIDI Setup. Check the broadcast level separately in BUTT.
Capture BlackHole in BUTT
Open BUTT's Settings → Audio and select BlackHole 2ch as the primary audio device. Keep secondary capture disabled for this walkthrough. Choose stereo, map the left and right inputs to channels 1 and 2, and select the same supported sample rate used above.
Allow BUTT's microphone/audio-input permission when macOS requests it, even though the source is virtual. If capture is silent, check System Settings → Privacy & Security → Microphone for BUTT and reopen the app after changing access.
Play a track and watch BUTT's meter. You should hear the local playback and see a signal in BUTT. Avoid excessive gain or clipping.
Connect to VosCast
Follow the BUTT setup guide for the server profile. Use the connection values from your own account:
| Account type | Connection settings |
|---|---|
| Icecast | Host, source username, broadcast password, and the exact mount point. Standard port requires TLS off; TLS port requires TLS on. |
| SHOUTcast | Host, displayed base Server port, and broadcast password. Do not add one to the port. |
Enter the host without a URL scheme, port, or path. Use MP3 at or below the account's Maximum Bitrate. Save the profile and press Play in BUTT.
Check your account's Quick Listen Link on another device with headphones. Do not play it on the broadcasting Mac through the Multi-Output Device: that would capture the delayed stream again and create a loop.
At the end, stop BUTT, restart hosted Auto DJ manually if needed, and return macOS Sound Output to your usual device.
Troubleshooting and adding a microphone
- You hear music but BUTT is silent: verify BlackHole is included in the Multi-Output Device and selected as BUTT's input. Check input permission and channels.
- BUTT has audio but headphones are silent: include the physical headphone output in the Multi-Output Device and check its volume.
- Crackling or playback will not start: check matching sample rates, the primary device, and drift correction. BlackHole's official guide includes additional advice for Macs that require the built-in output as the primary device.
- The microphone is missing: that is expected in this application-audio setup. An Aggregate Device groups inputs but does not automatically mix them into one stereo programme. A mixer or DAW must perform that routing. For a different Mac broadcasting workflow, see Audio Hijack.