Glossary
A¶
ADPCM — Adaptive Differential Pulse-Code Modulation. A lossy audio compression algorithm used by the AMS codec.
AllRAD — All-Round Ambisonic Decoding. A speaker-decoding method that decodes an Ambisonic sound field onto a dense virtual speaker array, then pans each virtual speaker to the real output layout. Used by the AmbisonicSpeakerDecoderNode for surround and custom speaker layouts.
am CLI — The official command-line tool for creating, building, and managing Amplitude projects. See the am CLI reference.
Ambisonics — A full-sphere surround sound technique using spherical harmonics to encode and decode 3D sound fields.
AMIR — Amplitude HRIR file format. An optimized binary format for storing Head-Related Impulse Response data.
AMS — Amplitude Media Stream. Amplitude's custom ADPCM-compressed audio file format.
Attenuation — The reduction of sound level as distance from the source increases.
B¶
B-Format — The channel representation of an Ambisonic signal (W, X, Y, Z, etc.).
Bus — An audio mixing channel that groups sounds together for shared gain, ducking, and effects processing.
C¶
Channel — A single instance of a playing sound in the mixer. Each Play() call creates a channel.
Channel Layout — A named output channel configuration (e.g., Stereo, 5.1, 7.1.4) describing how many speakers an engine output or pipeline node produces and where they are positioned. Set via the channels engine configuration property.
Codec — A software component that encodes and/or decodes audio data from a specific file format.
Collection — A sound object that groups multiple sounds and selects one to play based on a scheduler.
D¶
Decoder — The part of a codec that reads compressed audio data and produces raw PCM samples.
DSP — Digital Signal Processing. Mathematical manipulation of audio signals (filters, effects, etc.).
Ducking — Automatically reducing the gain of one bus when another bus becomes active.
E¶
Encoder — The part of a codec that writes raw PCM samples into a compressed audio file.
Entity — A game object in the Amplitude engine that can emit or receive spatialized audio.
Environment — A zone in 3D space where sounds receive a specific effect (reverb, EQ, etc.).
Event Mailbox — The mechanism by which voice lifecycle events (started, looped, ended, stopped, error) are queued on the audio thread and delivered to the game thread on a later frame. This is why channel event callbacks never fire synchronously at the exact moment the thing they describe happens.
F¶
Fader — A curve that controls how a value transitions from one point to another over time.
FlatBuffers — A binary serialization format used by Amplitude for project assets and configuration files.
Fold-down — Mixing a node's upstream channels down to mono (or another smaller layout) before processing, following ITU fold-down coefficients. Pipeline nodes opt into this with EnableFoldDown(). See Channel Policies and Surround Output.
H¶
HRTF — Head-Related Transfer Function. A pair of filters that capture how sound interacts with the human head and ears for 3D spatialization.
HRIR — Head-Related Impulse Response. The time-domain representation of an HRTF.
I¶
ILD — Interaural Level Difference. The difference in sound level between the two ears, used for localization.
ITD — Interaural Time Difference. The difference in arrival time of sound between the two ears, used for localization.
L¶
Listener — A point in 3D space that represents the player's ears. Audio is spatialized relative to listeners.
LZ4 — A fast lossless compression algorithm used by the ampk packager.
N¶
Node — A processing unit in the Amplimix pipeline. Nodes perform spatialization, effects, mixing, or dynamics.
P¶
Pipeline — A directed acyclic graph (DAG) of nodes that defines how audio is processed in the mixer.
R¶
Resampler — A component that converts audio from one sample rate to another.
Reverb Plugin — A registered Reverb/ReverbInstance implementation that provides a reverberation algorithm (e.g., Freeverb, Dattorro, RoomReverb). The Reverb pipeline node selects and drives one per layer. See Custom Reverb.
Room — A physically modeled acoustic space with walls, materials, and dimensions that affect reverberation.
RTPC — Real-Time Parameter Control. A game value (e.g., speed, health) that dynamically controls audio properties via curves.
S¶
Sound Bank — A binary asset pack that contains multiple sounds, collections, events, and other assets.
Sound Object — A generic term for any playable asset: Sound, Collection, or SwitchContainer.
Spatialization — The process of positioning audio in 3D space using panning, HRTF, or Ambisonics.
Spread — A sound property, in degrees (0–360), that controls the apparent width of a sound source during panning. See the spread property.
Switch Container — A sound object that plays different audio content based on the current state of a switch.
V¶
Virtual Channel — A channel that is not actively mixed but is still tracked by the engine. Virtual channels can be promoted to real channels when resources become available.
Voice — Another term for a channel or sound instance in the mixer.