Correct Ambisonic format conversion requires matching four parameters: order, component ordering, normalization, and reference radius

Different Ambisonic formats (ATK FOA, ATK HOA, AmbiX, A-format) can be incompatible in four distinct ways: (1) Order — how many spherical harmonic degrees are present; (2) Component ordering — the sequence of channels (WXYZ / Furse-Malham vs. ACN WYZX); (3) Component normalization — the gain coefficients applied to each channel (MaxN vs. N3D vs. SN3D); (4) Reference radius — the assumed wavefield distance (FOA=∞ i.e. planewave, HOA default=1.5 m). Mismatching any of these parameters distorts the soundfield: wrong ordering makes it go sideways, wrong normalization scales channels incorrectly, wrong radius introduces proximity filtering artefacts. The ATK’s Ambisonic Format Exchange guide provides conversion recipes. Converting HOA to FOA requires: (a) drop higher-order channels with .keep(4), (b) apply HoaNFProx to convert the reference radius (with a preceding HPF to prevent overflow), (c) apply the transcoder to handle ordering/normalization.

Examples

AmbiX (common in recordings online) uses ACN ordering + SN3D normalization + infinite radius. Decode it in ATK FOA: FoaEncoderMatrix.newAmbix1 handles the conversion. Converting HOA 3rd order to FOA for binaural: drop to 4ch, HoaNFProx, FoaEncoderMatrix.newHoa1.

Assessment

List the four parameters that must match for a correct Ambisonic format conversion. Explain what happens audibly if component ordering is wrong. Describe the SuperCollider conversion chain from 3rd-order HOA to ATK FOA B-format.