Ambisonic A-format (tetrahedral microphone raw output) is converted to B-format via a matrix transcoder with correct orientation

A tetrahedral soundfield microphone captures four cardioid capsules arranged in a tetrahedron and outputs a raw four-channel signal called A-format. A-format is NOT the same as B-format: it must be transcoded before any ATK processing can begin. In the ATK, FoaEncoderMatrix.newAtoB performs this conversion via matrix multiplication, requiring two parameters: orientation (which capsule is front-left-up, e.g. ‘flu’ or ‘flrd’) and weight (the capsule directionality pattern, typically ‘cardioid’). The orientation string describes the position of the lowest-indexed capsule when the microphone is upright and forward-facing; you must consult the microphone’s manual. Importantly, newAtoB is purely a matrix operation — it does NOT include capsule response equalisation or proximity filtering that commercial A-to-B converter software typically applies.

Examples

For a microphone with ‘flrd’ orientation and cardioid capsules: var enc = FoaEncoderMatrix.newAtoB('flrd', 'cardioid'); var bfmt = FoaEncode.ar(a_format_buf, enc); then decode as normal.

Assessment

Explain why the orientation string matters when converting A-format to B-format. List one processing step that newAtoB does NOT perform that commercial converters include.