This manual page documents briefly the ambdec and ambdec_cli commands.
AmbDec is an Ambisonics decoder for up to 36 speakers. It can be used for both horizontal and full 3-D
systems of first, second and third order. The decoding matrices are fully user-configurable. AmbDec has
some advanced features not found on most decoders:
Dualfrequencybandoperation. Optimal Ambisonics reproduction requires a different decoder for low and
high frequencies. This is so mainly because human perception of sound direction uses different mechanisms
at low and high frequencies. The crossover filters used in AmbDec are phase-aligned (the two outputs are
exactly in phase at all frequencies). The combined response is equivalent to a first-order all-pass
network, which is very probably inaudible.
Speakerdistancecompensation. If the speakers are not all at the same distance to the center of the
listening area, this must be compensated by including the right delays and gain corrections.
Near-fieldeffectcompensation. Ambisonics works by reconstructing the spherical harmonic components of
a sound field at the center of the listening area, using all speakers to synthesize each of them. All
non-zero order components show a near-field effect depending on the ratio wavelength=distance, and
increasing for rising order. One example of this is the well known 'proximity effect' of directional
microphones ('directional' is equivalent to 'using non-zero order components'). Except in very large
installations, where the speaker distances will be large enough so the listening area is not in the near
field, this effect must be compensated for in order to obtain a correct reconstruction of a sound field.