Ambisonics and VR/360 Audio in Pro Tools | HD

By in AES 2017, Audio Post, Pro Mixing

Pro Tools | HD 12.8.2 opens up new 3D audio workflows using Ambisonics, and gives you the tools to start creating virtual reality (VR)and 360 audio content with Facebook’s Spatial Workstation plug-ins, now included as standard with Pro Tools | HD.

Ambisonics is a system for capturing or representing a spherical sound field using regular audio channels. An Ambisonics mix is not tied to any particular playback system; it can be decoded to playback on any arrangement of speakers, or on headphones. It’s the audio format commonly used for Facebook 360 videos, as well as for 360 video on YouTube, and VR headsets like Oculus Rift and Gear VR.

Pro Tools 12.8.2 adds new bus and track formats for first, second and third order Ambisonics, providing the framework for plug-ins to create and manipulate Ambisonic audio and mixes. First Order busses have 4 channels, and are the format produced by traditional sound field microphones. Higher order Ambisonics uses more channels (9 for second Order, and 16 for third Order) to increase the positional resolution of point sources in your mix.

You Spin Me Right Round

You’ve probably watched 360 videos on your phone, or used a Head Mounted Display (HMD) such as Samsung Gear VR or Google Cardboard. These experiences present a complete spherical view in which you can look around, either by swiping with your finger or turning your head.

To create a truly immersive experience, you need an audio world as compelling as the visuals. Ambisonics is an ideal medium for 360 and VR sound as it carries a uniform surround audio field that can be matched with the visual experience at the point of playback.

In most cases, the sound of 360 video and VR is delivered via headphones. As you move your screen or turn your head, your device (phone, Rift, etc.) rotates the Ambisonics sound field to match your viewing direction and turns it into a stereo headphone feed. Binaural processing creates a convincing impression of sounds coming from all around, including from above and below. The results can be startling.

Ambisonics Workflows

Ambisonic audio content can be captured with Ambisonic mics, or found in Ambisonic sound libraries. Once in Pro Tools | HD these can be manipulated in various ways by plug-ins. For example, you could rotate the sound field, or isolate or rebalance sounds from specific directions.

But, this is only a small part of the picture. You can also create Ambisonic format content from the ground up using familiar post-production or music mixing workflows. Ambisonic panner plug-ins, like those in the Facebook Spatial Workstation collection and Audio Ease’s 360pan Suite, let you position mixed sources (mono, stereo, 5.1, etc.) into an Ambisonic mix.

In the accompanying video, you can watch how we created a Facebook-ready audio bed for our home-made 360 video from the 2017 IBC show. Each audio track uses the Spatialiser plug-in to convert its audio to second-order Ambisonics. The plug-in uses a flat video overlay display to make panning easy. Regular Pro Tools automation is used to track moving objects, or to keep sounds tied to their visual source when the camera is moving.

The Facebook Audio 360 format also provides for static (non-headtracked) elements in the mix, which can be used for voice over and music, for example. These are routed to a separate stereo mix bus in your project.

Getting Started

You can start working with Ambisonics and VR sound today if you have a current Pro Tools | HD Subscription or Upgrade & Support Plan. Log into your Avid Account and update to Pro Tools 12.8.2. The installer includes the Audio 360 Spatial Workstation plug-in suite.

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I’m a Pro Audio Solutions Specialist at Avid, with a background in sound design and mixing. I’m also a regular contributor to Sound on Sound magazine.