Quadrophonic

Hey @OneGobo,

This was exported from Logic Pro with Quadrophonic Surround settings.

Let me know if you have any other questions,
Michael

Thanks a lot Michael. Before seeing the example project I wasn't even aware of Reality Composer being able to use other formats than Stereo/Mono. I apologize if thats all in the docs and I missed it, but what other formats are possible? 4ch Ambisonics ie? Whats best practice for spatial sound as a balance of workload, size and effect in your experience? Most likely Quadrophonic since you picked it, right?

Thanks, Axel

Hey @OneGobo,

These are great questions! I chatted with the team and here's what I've learned.

The formats supported by RealityKit and transitively Reality Composer Pro are those which are described by a predefined audio channel layout tag whose channel descriptions have predefined coordinates. Specifically, this excludes formats with user-defined coordinates (e.g., UseChannelDescriptions) and ambisonic layouts (e.g., Ambisonic_B_Format, HOA_ACN_N3D, HOA_ACN_SN3D). In other words, all traditional multichannel layouts which are supported by the given codec and file type combination should be supported by Reality Composer Pro and RealityKit.

If you run into any unexpected behavior (e.g., errors thrown through the API, silence, etc.) please file Feedback! Once you file the request, please post the FB number here. If you're not familiar with how to file enhancement requests, take a look at Bug Reporting: How and Why?

We picked the Quadraphonic layout for the Spaceship's ambient musicscape for reasons described in the WWDC session, namely that there is no predefined "front" orientation and the channels are laid out equiangularly. It also uses one channel less than 5.0, so there is a tiny file size win there. In the Spaceship sample app, we use an AIFF file type with a PCM data type, so the channel count savings are dwarfed by the enormity of the uncompressed audio file. You may ask: why not use a lossless or lossy compressed audio codec to save some space? Neither ALAC (Apple Lossless) nor FLAC (Free Lossless) supports the Quadraphonic channel layout, but they do support other common cinematic channel layouts, so give those a try if this suits your use case! These codecs should give you in the ballpark of a 2X size reduction. AAC supports the Quadraphonic layout, however AAC with multichannel layouts is not supported on iOS-derived operating systems like visionOS.

You can use the afconvert command line utility provided in macOS to convert files to the different data and file types.

If you are looking to play multichannel audio content with more considerable file size compression, you can also look into the APAC codec. As of macOS Sequoia, you can use afconvert to convert your preexisting files into an APAC encoded file, which will work on macOS, iOS, and visionOS. APAC supports all of the multichannel layouts, including Quadraphonic.

Hope this helps, Michael