Stereo Imaging & Surround Speaker Mode Mixdown

I’m noticing that if you use Oculus Spatializer, the Surround Speaker Mode in Build Preferences needs to be set to a surround format instead of stereo. Stereo seems to be the intuitive choice since the spatializer is just binaural, 2-channel. But when using Stereo, there is a narrowing of the stereo field which I’m assuming is the result of the surround-to-stereo downmix matrix.

I know the plugin is not maintained by FMOD, but I’m just curious about the reason for this downmix behavior in a stereo project. Within a project where everything is stereo—events, busses, master output—why would a downmix matrix get involved? Even using the panner doesn’t reach a full stereo pan: hard left still bleeds into the right in the master out, though the event’s output and its group bus show no signal in the right channel.

Unfortunately, we could not find the answer to your question in the Oculus Spatializer’s documentation.

If you have questions about the design or behavior of software that are not answered by its documentation, you will have to contact that software’s developers. In this case, you will need to contact the Oculus support team.

Sorry, I should have been more clear to distinguish when talking about 3rd party plugins vs FMOD built-in ones. I meant that FMOD’s built-in panner also has this behavior, where a hard pan results in quite a bit of signal in the opposite channel, when using Stereo mode in build prefs. In a project with only stereo events/busses/master output (and with no 3rd party plugins), it seems that a downmix matrix is narrowing the stereo image. You can only achieve a hard pan in a stereo build by using FMOD’s Spatializer which would be the expected result from the surround-to-stereo matrix. My question is why is a downmix matrix involved in a fully stereo project.

Spatializing effects need to be able to dynamically spatialize the signal, which is to say, they need to be able to alter the signal’s panning, and thus the direction the sound seems to be coming from, at a moment’s notice. Using a downmix matrix for this means that the sound can seamlessly swing from any position around the listener to any other, retaining some of its apparent width while still changing position.