So I think I figured this out.
Most of the guidance on this subject assumes ( fairly ) that the user is going to bring in Ambisonic recordings ( 4 channel or more), plus mono/stereo audio and perhaps some VST instruments which will then all be mixed back into a final Ambisonic ( 4 channel … or more ) mix file.
This file would then have to be played through an ambisonic decoder for the audio to be delivered to the playback system ( speaker array, headphones etc) . Therefore the instructions I found choose to invoke the Nuendo Control Room which monitors the source tracks, and decodes them to Binaural/Stereo for convenient headphone monitoring. However the signal path is all Ambisonic and an Export will produce a true multi track Ambisonic file. That’s what I was experiencing.
As mentioned such an Ambisonic file would require a decoder for playback which could be inconvenient. If your final output will always be headphone or stereo speakers, then why not just create the final mix as a binaural / stereo file ? For headphones that’s what a decoder would do anyway.
So I went with just giving Nuendo a basic main Stereo output as below… no Ambisonic busses at all! That’s what I want to end up with. I disabled the Control Room… I want to hear the main out directly.
In Nuendo itself I created source audio tracks configured as First Order Ambisonic (1OA in the Create Track/Configuration drop down ) to hold real Ambisonic recordings.
I also created normal stereo/mono audio tracks for added elements.
The trick was to route all these source tracks to an Ambisonic Group Track ( create a Group track , set its Configuration to First Order Ambisonic/1OA) and send its output to the main stereo out as below.
so it it all looks as below
And that’s it. The true Ambisonic tracks will automatically have the VST Ambisonic decoder available for adjustment ( double click in the track panner ) and the normal audio tracks will have the Multi-panner available to position the sound in 3D. Monitoring will automatically be the stereo/binaural result of the mix and Exports will be two channel… but sound very spacious!
Insert effects work in all the tracks (EQ, etc although the only reverb that works is Reverence ). I tried a lot of Ambisonic plugins as inserts, but found they didn’t really improve things. The true Ambisonic tracks are best left unaffected.
Hope this helps someone else!