  The equatorial microphone array presented in (Ahrens et al., 2021) computes a
spherical harmonic (SH) representation of a sound field based on pressure
sensors along the equator of a rigid spherical baffle. The original formulation
uses complex-valued SH basis functions. This is inconvenient if the SH
representation of the captured sound field is intended to be stored in time
domain by means of real-valued audio signals as it is common in the spatial
audio format of ambisonics. The present document summarizes the modifications
that need to be applied to the mathematical formulation from (Ahrens et al.,
2021) to produce an ambisonic representation of the captured sound field that
is compatible with the established ambisonic software tools like SPARTA and the
IEM Plugin Suite. An example MATLAB script that implements this formulation is
provided.
