Ambisonics in FMOD

The Oculus FMOD OSP supports Oculus Ambisonics in the AmbiX (ACN/SN3D) format.

To apply Oculus Ambisonics to a sound file, select Oculus Ambisonics under Add Effect > Plug-in Effects.

Although ambisonics are not officially supported by FMOD Studio 1.8, the flexible bus architecture and multi-channel audio support allows ambisonics to work. However, there are some quirks to watch out for.

FMOD will upmix a 4-channel ambisonic sound file to 5.1 at the output of the audio track. This mixes the channels together in a way that interferes with the sound field. If you put a 4-channel ambisonic sound file on an audio track and the Oculus Ambisonics effect on the master track, it will not sound right.

There are two way to work around this:

1. Put the Oculus Ambisonics effect on the same Audio Track as the sound file.

Notice in the screenshot below that the meters on the “In” at the left side of the track shows 4 channels. This is the best approach if you wish to play back a single ambisonic sound or loop.

2. Convert your 4-channel ambisonics sound files to pseudo 5.1 files by converting them to 6 channels. Insert two silent channels between the ambisonics channel, so the third and fourth channels are silent, as shown below. This prevents FMOD from upmixing and passes through six channels to the Oculus Ambisonics, which knows to interpret that as ambisonic.

This approach works will if you are playing back several ambisonic sounds in one event and want to mix them together before spatializing. The most common use case for this is an interactive music mix using ambisonics.

For more information on Oculus Ambisonics, see the Oculus Ambisonics section of the Supported Features section of our Audio SDK Guide.