setup_audio.md

macOS Audio Setup for Meeting Recording

This tool captures both your microphone and system audio (e.g., the other person on a Zoom/Meet call). On macOS, this requires a virtual audio driver and some one-time configuration.

Prerequisites

Install BlackHole 2ch (free, open-source virtual audio driver):

brew install blackhole-2ch

Setup Steps

Open Audio MIDI Setup (search in Spotlight or find it in /Applications/Utilities/).

1. Create a Multi-Output Device

This lets you hear system audio normally while also routing it to BlackHole for capture.

1. Click the + button at the bottom-left → Create Multi-Output Device
2. Check these devices (in this order):
   • MacBook Pro Speakers (or your preferred output)
   • BlackHole 2ch
3. Rename it to Multi-Output (right-click → rename)
4. Make sure Drift Correction is checked for BlackHole 2ch

2. Create an Aggregate Device

This combines your microphone and BlackHole into a single input device the recorder can use.

1. Click the + button → Create Aggregate Device
2. Check these devices:
   • MacBook Pro Microphone (or your preferred mic)
   • BlackHole 2ch
3. Rename it to Aggregate (right-click → rename)
4. Make sure Drift Correction is checked for BlackHole 2ch

3. Set System Output

Before starting a meeting:

1. Go to System Settings → Sound → Output
2. Select Multi-Output as your output device

This ensures system audio plays through your speakers AND gets captured by BlackHole.

How It Works

Your mic ──────────────────────┐
                               ├──→ Aggregate Device ──→ murmur recorder
System audio ──→ Multi-Output ─┤
                   ├──→ Speakers (you hear it)
                   └──→ BlackHole 2ch ─┘

Verify Setup

python -m murmur devices

You should see Aggregate and Multi-Output in the device list.

Notes

• You can adjust the sample rate of BlackHole in Audio MIDI Setup (default 48000 Hz matches this tool's settings)
• If you get "no input channels" errors, make sure your Aggregate Device has at least one input device checked
• After a meeting, switch your output back to normal speakers if you don't want the Multi-Output routing active