HOA Technical Notes - N3D

N3D is a alternative representation of B-Format with lots of useful mathematical properties. It appears in quite a lot of the Higher Order Ambisonic literature and Rapture3D uses a variant of N3D for all its internal processing.

We recommend that N3D be stored with using the ACN channel ordering sequence (see http://ambisonics.ch/standards/channels/). But be careful - although most software seems to use this convention, there are variants out there, so you may need to reorder your channels.

There have been a few attempts to implement N3D encoding in software that have ended up being slightly wrong. You may wish to download the rambl.tgz archive, which provides a reference implementation of the N3D equations in C using the ACN channel ordering sequence. It's not fast, but it is correct (hopefully!).