Appendix A: Glossary

Working definitions, tuned to how this book uses each term. Chapter references point to the fuller treatment.

A-format — The raw four-capsule output of a tetrahedral ambisonic microphone, before matrixing. Not usable directly. (Ch. 19)

ACN — Ambisonic Channel Number; the modern channel ordering, acn = n(n+1) + m. W=0; Y,Z,X = 1,2,3. Half of AmbiX. (Chs. 6, 8)

ALLRAD — Decoder construction: sample to an ideal virtual layout, then VBAP-pan the virtual speakers onto the real ones. The safe choice for irregular/gappy arrays. (Ch. 12)

AmbiX — The modern ambisonic convention: ACN ordering + SN3D scaling. What AmbiTap and everything current speaks. (Ch. 8)

Ambisonics — The scene-based spatial audio paradigm: store the directional soundfield at a point as spherical-harmonic components; decode at playback. (Ch. 2)

Azimuth / elevation — Direction angles: azimuth 0 = front, positive counterclockwise from above (+90° = left); elevation 0 = horizon, +90° = zenith. Radians in AmbiTap objects. (Ch. 3)

B-format — An ambisonic signal set; historically first-order FuMa, loosely any ambisonic bus today. Ask order/ordering/normalization. (Chs. 6, 8)

Bed — A channel-based base layer (5.1, 7.1.4) in an otherwise object- or scene-based mix. Folded into scenes with bed2hoa~. (Chs. 17, 22)

Binaural — Two-channel audio that reproduces the ear-entrance signals — rendered through HRTFs, headphones assumed. (Chs. 1, 13)

Channel-based — The paradigm where the stored channels are the speaker feeds (stereo, 5.1, 7.1.4). (Ch. 2)

Cone of confusion — The set of directions sharing (nearly) the same ITD/ILD; broken by pinna spectra and head movement. (Ch. 1)

Crosstalk cancellation (XTC / transaural) — Pre-filtering two speaker feeds so binaural signals survive the trip through open air to one listener's ears. (Ch. 16)

Decoder — The matrix (and philosophy) turning scene channels into speaker feeds: mode-matching, ALLRAD, EPAD. (Chs. 5, 12)

Doppler — Pitch shift from changing propagation delay; the strongest "really moving" cue. (Ch. 10)

Energy vector (rE) — Loudness-weighted mean direction of a decode or scene; its magnitude predicts image focus. The instrument energyvec~ tracks the scene's. (Chs. 12, 14)

EPAD — Energy-preserving decoder construction (SVD-based). (Ch. 12)

Externalization — Hearing sound out there rather than inside the head on headphones; helped most by rooms, MagLS, and tracking. (Chs. 11, 13)

FuMa — The historical convention (Furse–Malham): W,X,Y,Z order, W at −3 dB, defined to order 3. Convert at the border with format~. (Ch. 8)

HOA — Higher-Order Ambisonics: order ≥ 2, (N+1)² channels. (Chs. 2, 7)

HRTF / HRIR — Head-Related Transfer Function (frequency view) / Impulse Response (time view): per-direction filters from source to each eardrum; the raw material of binaural rendering. (Ch. 13)

ILD / ITD — Interaural Level / Time Difference: the two lateral-localization cue families. (Ch. 1)

KEMAR — The standard measurement mannequin whose HRTF set is embedded in AmbiTap (MIT dataset, SH-projected to order 5). (Ch. 13)

LFE — Low-Frequency Effects channel (the ".1"): a delivery convention, not a direction; routed around the bus. (Ch. 17)

MagLS — Magnitude least-squares HRTF projection: sacrifices high-frequency phase to preserve magnitude at low order; the modern binaural default. (Ch. 13)

max-rE — Per-order weighting that maximizes the energy-vector magnitude — cleaner concentration above the reconstruction limit. A decoder attribute and a beam flavor. (Chs. 5, 7, 12)

Mid-side (M/S) — Stereo technique (omni-ish mid + sideways figure-8); B-format's two-channel ancestor in spirit. (Ch. 6)

Mode-matching — Decoder construction by (pseudo)inverting the re-encoding matrix; faithful on healthy layouts, strained on gappy ones. (Ch. 12)

N3D — Orthonormal scaling cousin of SN3D (higher orders hotter by √(2n+1)); appears in research tools. (Ch. 8)

NFC — Near-field compensation: correcting the bass boost of wavefront curvature for close sources. (Ch. 10)

Object-based — The paradigm storing dry sources + position metadata, rendered at playback (Atmos, game engines). (Chs. 2, 22)

Order (N) — The spherical-harmonic degree cap of a scene: (N+1)² channels; sharpness ~1/N; this book defaults to 3. (Ch. 7)

Pinna cues — Direction-dependent spectral fingerprints from the outer ear; carry elevation and front/back. Personal. (Ch. 1)

Precedence effect — The first-arriving wavefront dominates localization; why off-center listeners hear the nearest speaker. (Chs. 1, 5)

rE — see Energy vector.

Scene-based — The paradigm of this book; see Ambisonics. (Ch. 2)

SN3D — The AmbiX level scaling: no channel exceeds W for a single source. (Chs. 6, 8)

SOFA — Standard file format for measured HRTF sets; accepted by binaural~ (Max) for personalized ears. (Ch. 13)

Soundfield — The pressure-and-direction state of sound at a point; what a scene stores and an ambisonic mic records. Also the historical microphone brand. (Chs. 2, 19)

Spherical harmonics (SH) — The basis functions on the sphere; each ambisonic channel is one, readable as a mic pickup pattern. (Ch. 6)

Sweet spot — The listening region where reproduction holds together; grows with order and decoder care. (Chs. 5, 7)

T-design — A uniform point set on the sphere (used as ALLRAD's virtual layout and in the library's internals). (Ch. 12)

VBAP — Vector-Base Amplitude Panning: pan a source onto the nearest 2–3 speakers; the object-renderer workhorse, and ALLRAD's second stage. (Chs. 2, 12)

Virtual microphone — A beam extracted from a scene in a chosen direction (vmic~); resolution set by order. (Ch. 15)

W — Channel 0: the omni component; a correct mono mix of the scene; the key signal for image-preserving dynamics. (Chs. 6, 15)