5.1 & 7.1 mixdown and stereo monitoring

How does FMOD mixdown from any surround format (including 7.1.4) to stereo if the platform is not using a surround format? I read in the forums that you did away with SRS. What is the new method? And is there any officially sanctioned way to monitor how the mixdown will sound from within FMOD Studio? If I simply change the output bus back and forth from surround to stereo, my worry is losing surround panning and routing, or other potential unforeseen side effects. Would doing this be an accurate reflection of runtime mixdown? It would be great to have a simpler at-your-fingertips way of monitoring FMOD’s mixdown behavior on the fly.

The way that FMOD handles the downmix for any surround format to stereo is by using a mix matrix, although at this point we do not have this available in our docs, in the case of 7.1.4 the height speakers just get removed leaving 7.1.

In FMOD 2.00.00, the special case of 5.1 to stereo that used SRS downmix was removed, now FMOD makes use of mix matrices for all downmixes.

Currently there isn’t a way to monitor the mixdown visually from within Studio, the best way is to change your OS settings to different speaker configurations.

I have added a task to improve/add documentation around this subject as there is very little information on it in our docs currently.

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What dB values does the mix matrix use for the downmixes? I assume C is the standard -3dB, but what does the mix matrix do to the surround channels and LFE in 5.1 and 7.1 → stereo? It seems that the documentation has not yet been clarified with this.

I would need this info urgently as I’m just upmixing content to 5.1 for FMOD where the stereo downmix is still a priority, and have a very tight deadline…

(On an unrelated note, dropping the ceilings for 7.1.4 doesn’t seem like the best idea. Dolby has a different idea with Atmos, at least)

Same problem here, get worse if console monitoring is needed:
For example, I set Switch to 7.1 as system preferences (that should be the max number of channels in the best case scenario, that is Switch is connected via dock to a 7.1 system). Using “auto” as format in the master output in the mixer, and connecting to a console that is set to stereo (handeld mode) result in fmod showing and monitoring anyway the 7.1 channels, thus not actually monitoring the real headphones audio and preventing real time tuning.
What is the best way to setup this in order to avoid this issue? Put everything to stereo, mix in stereo, then back to 7.1 when shipping, and let the mix automatically adjust itself?

I could be wrong but I think Switch only supports up to 5.1, which isn’t a big deal if you’re also releasing for other platforms that support higher. But if you’re only releasing on Switch, at least your mixdown would be less involved if you mix in 5.1.

Have you tried Cameron’s solution yet? Monitoring a surround mixdown works pretty well by changing the output device in FMOD Audio preferences. Selecting built-in output on a Mac and plugging headphones in works. If you’re on a Mac you can also create output devices for different purposes and channel routing. I have a custom “FMOD” one and an “FMOD Stereo” one just for monitoring a mixdown.

It’s a little unobvious to set up: In Audio MIDI Setup, make a “Multi-Output Device”, select the check mark on “Built-in Output” FIRST, then your interface. Not sure why the order matters. Then configure speakers, select stereo. Super easy to switch between these output devices in FMOD Prefs.

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Bringing back this topic. I would very gladly like to know too how the internal matrix works, there is just no way to know at the moment.

Thank you

Here is some additional information on downmixing: