Loudness in Dolby Atmos in Logic Pro: A step-by-step-guide

This article dives deep into how you can best measure loudness when mixing in Dolby Atmos using Logic Pro. The tips we discuss in this article are tailored for use of only Logic’s own plug-ins. If you want to read something more fundamental, you can check out our article on what a workflow in Dolby Atmos might look like, or our article that covers what Dolby Atmos is all about.

Measuring Loudness in ADM Files for Dolby Atmos in Logic Pro: A Step-by-Step Guide

When working with ADM files (Audio Definition Model) — i.e., in Dolby Atmos — in Logic Pro, it’s important to measure loudness accurately, especially if your mix is intended for streaming or playback in the spatial audio format. This article guides you through how to measure LUFS (Loudness Units Full Scale) and TPdB (True Peak dB) for an Atmos mix, using the tools available in Logic. However, for the most accurate measurement, it’s best to use Dolby Atmos Renderer (Dolby’s own software for handling ADM files), which also enables the creation of a spatial audio version of the mix. In this article, we will, however, assume that the only available tools are those included in Logic Pro.

Step 1: Preparation for Measurement

1. Activate Dolby Atmos: Start by ensuring that Dolby Atmos is enabled in your project. Go to Menu → Mix → Dolby Atmos.
2. Add Logic’s Loudness Plugin: After adding the Atmos plugin to the master bus, also add Logic’s “Loudness” plugin to measure LUFS and true peak.
3. Atmos Plugin Settings:
   – Open the Atmos plugin and set the Monitoring Format to 7.1.4.
   – Click on the small menu to the right in the Atmos window to display options for the Binaural Renderer. Do not change any settings here, but note that these can be adjusted later depending on how you want the mix to sound in headphones.
   – Proceed to the Downmix & Trim tab:
   • Under Downmix Controls, set “5.1 and 5.1.x” to “Direct with room balance.”
   • Under Trim Controls, go through all four tabs and change “Automatic” to “Manual” for each tab. Ensure all sliders are set to 0dB or 0%.
4. Prepare the Song: Set the start and end points for the song using Cycle Range. This will ensure that the export includes the entire song in the analysis.
5. Loudness Plugin: Open Logic’s “Loudness” plugin, ensuring it is placed after the Atmos plugin in the signal path.

Step 2: Start the Measurement

1. Export the Mix: Press Start in the Loudness plugin, and use the shortcut Command + B to begin the bounce/export process. If you have used the meter before, press “Reset” before starting.
2. Set Up the Export:
   • Destination: PCM
   • Start/End: As is
   • Mode: Offline
   • Include Audio Tail: No
   • Include Tempo Information: Yes
   • Normalize: Off
   • File Format: Wave
   • Bit Depth: 24
   • Sample Rate: 48kHz
   • File Type: Interleaved
   • Dithering: None
   • Surround Bounce: Yes
   • Add to Project: No
3. Start the Export: Click OK to begin the export and measurement.

Step 3: Analyze the Results

After the export, you will have a LUFS value. A target should be to keep the volume around -18 LUFS to ensure that the mix does not become too loud for streaming platforms. If the value is higher than -18 LUFS, you should adjust the volume downward.

Step 4: Adjust the Volume with VCA

If the mix sounds good but just needs a volume adjustment, you can use a VCA (Voltage Controlled Amplifier) to adjust all output stations (buses or objects) in the mix. Here’s how to do it:

1. Create a VCA:
   • Go to Logic’s mixer and right-click on a track. Select Channel Strip Components → VCA.
   • Select all output stations (buses or objects) and click the VCA field under the Pan symbol in the mixer.
   • Choose Create a new VCA for the selected channel strips.
2. Adjust Loudness: Use the VCA fader to adjust the volume until you reach the desired LUFS value.

Step 5: Measuring the Binaural Version

To measure loudness on the binaural mix, follow these steps:

1. Open the Atmos plugin and set the Monitoring Format to Dolby Renderer.
2. Export the Binaural Mix: Follow the same steps as for the ADM export, but ensure that Surround Bounce is not checked.
3. Analyze the Binaural File: After exporting, you can import the file into Logic and use Logic’s MultiMeter plugin to analyze LUFS and true peak. Print the results and ensure that your binaural mix stays around -16 LUFS total, which is standard for streaming services.

Step 6: Finalization and ADM Export

When you are satisfied with your mix, you can export the entire project as an ADM file for distribution:

1. Go to Menu → File → Export → Project as ADM BWF.
   The ADM file will serve as your master, but you also need to create a stereo master. This is easiest done by using the binaural version. Export a binaural version and use it as the basis for your stereo master. Make sure it stays within the standard volumes required for stereo mastering.

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