RAMBL - A N3D/SN3D Reference Software Implementation
N3D and SN3D are representations of ambisonic B-Format with useful mathematical properties. They are common in the Higher Order Ambisonic literature and our plugins use SN3D.
We strongly recommend that N3D and SN3D be stored using the ACN channel ordering sequence. Also, be careful not to confuse N3D and SN3D. They are similar and easy to convert, but they are not directly compatible with each other.
There have been a few attempts to implement these encodings that have ended up being slightly wrong. You may wish to download the RAMBL archive, which provides a reference implementation of the N3D and SN3D equations in C using the ACN channel ordering sequence. It's not fast, but it is correct (hopefully!).
SN3D is also used in YouTube Spatial Audio and the AmbiX file format.