Technical Notes
Technical notes on Higher Order Ambisonics and related subjects.
So, I hear you ask, "what is this Higher Order Ambisonics thing?"
Well, it's quite a few things. Probably more than anything, it's a mathematical framework in which 3D audio can be handled. It uses a representation of the soundfield centred around a listener at the centre of the room.
"Amber" is a new decoder method that's available on headphones and speakers in Rapture3D 2.4.11. We're quite excited about it.
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.
B-Format is the main audio format used for Higher Order Ambisonics. This is a multichannel audio format where the individual channels do not correspond directly to speaker feeds. There is no "front left" channel.
In Higher Order Ambisonics, the main audio stream in use is B-Format. This contains an awful lot of information about sound directivity, and it is deliberately unaware of the speakers that you will use for playback. Because of this, it must be "decoded" for playback.
Once you have a B-Format audio stream, it's possible to manipulate it in various ways. For instance, you can rotate it using matrix multiplication. This moves all material in the soundfield.
First of all, what is 7.1? Well, 7.1 is a speaker layout and sound format used for surround sound. It expects seven normal speakers and one subwoofer (bass) speaker, and these are set out roughly in a circle around the listener (we say roughly, but there are recommended angles). Quite a few computers and Hi-Fis now support this layout. But, it's not 3D. Because all the channels are at the same height, it's hard to make sounds appear to come from above or below.