Incompatibility with existing HOA Ambisonics implementations

[kronihias]

Hi,
as already discussed via Email the implementation of the spherical harmonics has some problems..
The 3d implementation is not compatible to other implementations that have become standard (ambix) - as implemented in the ambix vst plugins and O3A by blueripplesound.

One cause:
In https://github.com/CICM/HoaLibrary-Light/blob/master/Sources/Encoder.hpp#L1208 you write
m_cos_theta = std::cos(HOA_PI2 + m_elevation);, this is a wrong conversion from elevation to zenith angle and results in flipping top/bottom. Correctly it should be: m_cos_theta = std::cos(HOA_PI2 - m_elevation);

Condon Shortley phase:
You are using somewhere the term (-1)^degree, which no other Ambisonics implementation I know of uses. Please remove for compatibility reasons.

Normalization:
the channels with degree=0 seems to be not scaled by 1/sqrt(4*pi).
I would recommend removing the term 1/sqrt(4*pi) completely, however if you decide to include it please do it consequently.

Best,
Matthias

[pierreguillot]

The normalization and the elevation problem were already corrected on the branch v2.3 (and now v3). I'm working on the other problem.

[pierreguillot]

The Condon Shortley phase problem should also be solved on the branch v3 !

[kronihias]

As soon as you have a new build for Max I'll test and check.
Thanks, Matthias

[elsueno]

Are all these issues fixed in the SN3D Patch from 05/23/2017?

[pierreguillot]

Yes