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npx -y skills add https://github.com/thedivergentai/gd-agentic-skills --skill godot-audio-systemsDescription
godot audio systems
SKILL.md
---
name: godot-audio-systems
description: "Expert patterns for Godot audio including AudioStreamPlayer variants (2D positional, 3D spatial), AudioBus mixing architecture, dynamic effects (reverb, EQ,compression), audio pooling for performance, music transitions (crossfade, bpm-sync), and procedural audio generation. Use for music systems, sound effects, spatial audio, or audio-reactive gameplay. Trigger keywords: AudioStreamPlayer, AudioStreamPlayer2D, AudioStreamPlayer3D, AudioBus, AudioServer, AudioEffect, music_crossfade, audio_pool, positional_audio, reverb, bus_volume."
---
# Audio Systems
Expert guidance for Godot's audio engine and mixing architecture.
## NEVER Do (Expert Audio Rules)
### Mixing & Buses
- **NEVER set bus volume with linear values** — `set_bus_volume_db()` is logarithmic. Use `linear_to_db()` for sliders OR everything will sound too loud until the last 5%.
- **NEVER skip 'Bus Routing'** — Playing music on the 'SFX' bus makes volume menus useless. Strictly route every player to its dedicated sub-bus (Music, SFX, UI, Voice).
- **NEVER use 'Master' for gameplay sounds** — Dedicate Master to final limiting. Route all gameplay to sub-groups so you can mute/duck categories.
### Positional & Spatial
- **NEVER use 3D players without an Attenuation Model** — Default is NONE. If you don't set it to `Inverse Distance`, a whisper on the other side of the map will be global volume.
- **NEVER play 3D sounds exactly on top of the listener** — Causes "Panning Jitter" where the sound snaps between Left/Right speakers. Offset by `0.1` units.
- **NEVER forget Doppler for high-speed objects** — A car flying by without `DOPPLER_TRACKING_PHYSICS_STEP` feels flat and static.
### Performance & Polish
- **NEVER spam same-frame sounds** — Playing 50 explosions at once causes constructive interference (clipping/distortion). Use a `Limiter` (`audio_voice_limiter_manager.gd`).
- **NEVER instantiate nodes for one-shots** — Creating a node, playing a 0.5s clap, and `queue_free()`ing causes frame-time spikes. Use a Pool.
- **NEVER skip Crossfades/Transitions** — Abrupt music cuts break immersion. Always use a 0.5s-1.0s `Tween` to bridge tracks.
---
## Godot 4.7: Audio Breaking Changes
- `AudioEffectSpectrumAnalyzer.tap_back_pos` **removed** — migrate analyzers to alternative tap APIs.
- `AudioStreamPlayer` default `area_mask` is now **0** (disabled), not layer 1. If using `Area2D`/`Area3D` `audio_bus_override`, explicitly set `area_mask` to layer 1 or your bus layer.
## Available Scripts
> **MANDATORY**: Read the appropriate script before implementing the corresponding pattern.
### [audio_voice_pool_manager.gd](scripts/audio_voice_pool_manager.gd)
Expert high-performance voice pooler with priority-based 'voice stealing' logic.
### [audio_occlusion_raycast.gd](scripts/audio_occlusion_raycast.gd)
Professional Raycast-based audio occlusion for dynamic muffling behind walls.
### [audio_interactive_music_manager.gd](scripts/audio_interactive_music_manager.gd)
Manager for vertical music layering using AudioStreamSynchronized for dynamic intensity.
### [audio_reactive_visualizer_component.gd](scripts/audio_reactive_visualizer_component.gd)
Expert FFT spectrum analysis component for driving logic-to-data visuals.
### [audio_bus_ducker_logic.gd](scripts/audio_bus_ducker_logic.gd)
Professional sidechain-style bus ducking (Dialogue-over-Music).
### [audio_procedural_generator_synth.gd](scripts/audio_procedural_generator_synth.gd)
Expert real-time synthesizer for procedural hums, engines, and signals.
### [audio_environmental_reverb_zone.gd](scripts/audio_environmental_reverb_zone.gd)
Dynamic reverb/bus effect management via Area3D trigger zones.
### [audio_voice_limiter_manager.gd](scripts/audio_voice_limiter_manager.gd)
Concurrency manager that prevents 'Ear Bleed' by capping identical SFX instances.
### [audio_linear_volume_interpolator.gd](scripts/audio_linear_volume_interpolator.gd)
Expert helper for smooth, musically-accurate UI volume slider mapping.
### [audio_footstep_surface_selector.gd](scripts/audio_footstep_surface_selector.gd)
Physics-driven surface detection and sound-bank selector for footsteps.
---
## AudioStreamPlayer Variants
### AudioStreamPlayer (Global/UI)
```gdscript
# No spatial positioning, same volume everywhere
# Use for: Music, UI sounds, voiceovers
@onready var music := AudioStreamPlayer.new()
func _ready() -> void:
music.stream = load("res://audio/music_main.ogg")
music.volume_db = -10 # Quieter
music.autoplay = false
music.bus = "Music" # Route to Music bus
add_child(music)
music.play()
```
### AudioStreamPlayer2D (Positional)
```gdscript
# 2D panning based on distance from camera
# Use for: 2D games, top-down audio cues
extends Area2D
@onready var footstep := AudioStreamPlayer2D.new()
func _ready() -> void:
footstep.stream = load("res://audio/footstep.ogg")
footstep.max_distance = 500 # Audible range (pixels)
footstep.attenuation = 2.0 # Falloff curve (higher = faster fadeout)
add_child(footstep)
func play_footstep() -> void:
if not footstep.playing:
footstep.play()
```
### AudioStreamPlayer3D (Spatial)
```gdscript
# 3D spatial audio with doppler, reverb send
# Use for: 3D games, realistic sound positioning
extends Node3D
@onready var explosion := AudioStreamPlayer3D.new()
func _ready() -> void:
explosion.stream = load("res://audio/explosion.ogg")
explosion.unit_size = 10.0 # Size of sound source
explosion.max_distance = 100.0 # Range
explosion.attenuation_model = AudioStreamPlayer3D.ATTENUATION_INVERSE_DISTANCE
explosion.doppler_tracking = AudioStreamPlayer3D.DOPPLER_TRACKING_PHYSICS_STEP
add_child(explosion)
explosion.play()
```
---
## AudioBus Architecture
### Bus Setup (Project Settings)
```
Master (always exists)
├─ Music
│ └─ Effects: Compressor, EQ
├─ SFX
│ └─ Effects: Reverb (for environment)
└─ Ambient
└─ Effects: LowPassFilter (muffled ambience)
```
### Volume Control (Decibels)
```gdscript
# ❌ BAD: Linear volume (doesn't work)
AudioServer.set_bus_volume_db(music_bus_idx, 0.5) # WRONG!
# ✅ GOOD: Use decibels
var music_bus := AudioServer.get_bus_index("Music")
AudioServer.set_bus_volume_db(music_bus, -10) # -10 dB (quieter)
# Convert linear (0.0-1.0) to dB:
var linear_volume := 0.5 # 50%
var db := linear_to_db(linear_volume) # ~-6 dB
AudioServer.set_bus_volume_db(music_bus, db)
# Convert dB to linear:
var current_db := AudioServer.get_bus_volume_db(music_bus)
var linear := db_to_linear(current_db)
print("Current volume: %d%%" % int(linear * 100))
```
### Mute Bus
```gdscript
func toggle_mute(bus_name: String) -> void:
var bus_idx := AudioServer.get_bus_index(bus_name)
var is_muted := AudioServer.is_bus_mute(bus_idx)
AudioServer.set_bus_mute(bus_idx, not is_muted)
```
---
## Audio Pooling (Performance)
### Problem: Creating Players Every Frame
```gdscript
# ❌ BAD: Creates 60 new nodes/second at 60 FPS
func play_footstep() -> void:
var player := AudioStreamPlayer.new()
add_child(player)
player.stream = load("res://audio/footstep.ogg")
player.finished.connect(player.queue_free)
player.play()
# Result: 3600 nodes created in 1 minute!
```
### Solution: Audio Pool
```gdscript
# audio_pool.gd (AutoLoad)
extends Node
const POOL_SIZE = 10
var pool: Array[AudioStreamPlayer] = []
var pool_index := 0
func _ready() -> void:
# Pre-create players
for i in range(POOL_SIZE):
var player := AudioStreamPlayer.new()
player.bus = "SFX"
add_child(player)
pool.append(player)
func play_sound(stream: AudioStream, volume_db := 0.0) -> void:
var player := pool[pool_index]
pool_index = (pool_index + 1) % POOL_SIZE # Round-robin
# Stop previous sound if still playing
if player.playing:
player.stop()
player.stream = stream
player.volume_db = volume_db
player.play()
# Usage:
AudioPool.play_sound(load("res://audio/coin.ogg"), -5.0)
```
---
## Music Transitions
### Crossfade Between Tracks
```gdscript
# music_manager.gd (AutoLoad)
extends Node
@onready var track_a := AudioStreamPlayer.new()
@onready var track_b := AudioStreamPlayer.new()
var current_track: AudioStreamPlayer
var fade_duration := 2.0
func _ready() -> void:
track_a.bus = "Music"
track_b.bus = "Music"
add_child(track_a)
add_child(track_b)
current_track = track_a
func crossfade_to(new_stream: AudioStream) -> void:
var next_track := track_b if current_track == track_a else track_a
# Start new track at 0 dB
next_track.stream = new_stream
next_track.volume_db = -80 # Silent
next_track.play()
# Fade out current, fade in next
var tween := create_tween().set_parallel(true)
tween.tween_property(current_track, "volume_db", -80, fade_duration)
tween.tween_property(next_track, "volume_db", 0, fade_duration)
await tween.finished
# Stop old track
current_track.stop()
current_track = next_track
```
### BPM-Synced Transitions
```gdscript
# Transition on beat boundary
var bpm := 120.0 # Beats per minute
var beat_duration := 60.0 / bpm # 0.5s per beat
func queue_transition_on_beat(new_stream: AudioStream) -> void:
# Wait for next beat
var current_time := current_track.get_playback_position()
var time_to_next_beat := beat_duration - fmod(current_time, beat_duration)
await get_tree().create_timer(time_to_next_beat).timeout
crossfade_to(new_stream)
```
---
## Dynamic Audio Effects
### Add Effect at Runtime
```gdscript
# Add reverb to SFX bus
var sfx_bus := AudioServer.get_bus_index("SFX")
var reverb := AudioEffectReverb.new()
reverb.room_size = 0.8 # Large room
reverb.damping = 0.5
reverb.wet = 0.3 # 30% effect, 70% dry
AudioServer.add_bus_effect(sfx_bus, reverb)
```
### Underwater Effect
```gdscript
func set_underwater(enabled: bool) -> void:
var sfx_bus := AudioServer.get_bus_index("SFX")
if enabled:
# Add low-pass filter (muffled sound)
var lowpass := AudioEffectLowPassFilter.new()
lowpass.cutoff_hz = 500 # Cut frequencies above 500 Hz
AudioServer.add_bus_effect(sfx_bus, lowpass)
else:
# Remove all effects
for i in range(AudioServer.get_bus_effect_count(sfx_bus)):
AudioServer.remove_bus_effect(sfx_bus, 0)
```
---
## Procedural Audio
### Synthesize Beep
```gdscript
# Generate simple sine wave
func create_beep(frequency: float, duration: float) -> AudioStreamGenerator:
var stream := AudioStreamGenerator.new()
stream.mix_rate = 44100 # Sample rate
var playback := stream.instantiate_playback()
var increment := frequency / stream.mix_rate
var phase := 0.0
for i in range(int(stream.mix_rate * duration)):
var sample := sin(phase * TAU)
playback.push_frame(Vector2(sample, sample)) # Stereo
phase += increment
phase = fmod(phase, 1.0)
return stream
# Usage:
var beep_stream := create_beep(440.0, 0.1) # 440 Hz (A4), 0.1s
$AudioStreamPlayer.stream = beep_stream
$AudioStreamPlayer.play()
```
---
## Advanced Patterns
### Audio Ducking (Lower Music During Dialogue)
```gdscript
# auto_duck.gd (on Dialogue AudioStreamPlayer)
extends AudioStreamPlayer
func _ready() -> void:
playing.connect(_on_playing)
finished.connect(_on_finished)
func _on_playing() -> void:
# Duck music to -15 dB
var music_bus := AudioServer.get_bus_index("Music")
var tween := create_tween()
tween.tween_method(set_music_volume, 0.0, -15.0, 0.5)
func _on_finished() -> void:
# Restore music to 0 dB
var tween := create_tween()
tween.tween_method(set_music_volume, -15.0, 0.0, 0.5)
func set_music_volume(db: float) -> void:
var music_bus := AudioServer.get_bus_index("Music")
AudioServer.set_bus_volume_db(music_bus, db)
```
### Randomize Pitch for Variation
```gdscript
# Prevent identical sounds (footsteps, gunshots)
func play_varied_sound(stream: AudioStream) -> void:
$AudioStreamPlayer.stream = stream
$AudioStreamPlayer.pitch_scale = randf_range(0.9, 1.1) # ±10% pitch
$AudioStreamPlayer.play()
```
### Layered Music (Adaptive)
```gdscript
# Intensity-based music layers (start quiet, add layers as intensity increases)
# Example: Peaceful exploration → Combat
@onready var layer_drums := $Music/Drums
@onready var layer_bass := $Music/Bass
@onready var layer_melody := $Music/Melody
var intensity := 0.0 # 0.0 = calm, 1.0 = intense
func _ready() -> void:
# Start all layers in sync
layer_drums.play()
layer_bass.play()
layer_melody.play()
# Mute high-intensity layers
layer_bass.volume_db = -80
layer_melody.volume_db = -80
func set_music_intensity(new_intensity: float) -> void:
intensity = clamp(new_intensity, 0.0, 1.0)
# Fade in layers based on intensity
var tween := create_tween().set_parallel(true)
# Layer 1 (drums): always audible
tween.tween_property(layer_drums, "volume_db", 0, 1.0)
# Layer 2 (bass): fade in at 33% intensity
var bass_db := -80 if intensity < 0.33 else lerp(-80.0, 0.0, (intensity - 0.33) / 0.67)
tween.tween_property(layer_bass, "volume_db", bass_db, 1.0)
# Layer 3 (melody): fade in at 66% intensity
var melody_db := -80 if intensity < 0.66 else lerp(-80.0, 0.0, (intensity - 0.66) / 0.34)
tween.tween_property(layer_melody, "volume_db", melody_db, 1.0)
# Usage (combat system):
func _on_enemy_spotted() -> void:
MusicManager.set_music_intensity(1.0) # Full intensity
func _on_all_enemies_defeated() -> void:
MusicManager.set_music_intensity(0.0) # Back to calm
```
---
## Expert Audio Patterns
### 1. Subtitle-Sync-System
Standard pattern for perfectly timed dialogue using `AnimationPlayer`.
- **Tracks**: Use an **Audio Playback Track** for the voice-over and a **Call Method Track** to trigger subtitles.
- **Localization**: Pass a translation key (e.g., `show_subtitle("VO_LINE_01")`) as the method argument. The subtitle script uses `tr()` to fetch the localized text, ensuring perfect sync across all languages.
### 2. Audio-Occlusion-Profiling (Dynamic Muffling)
Simulate sound muffling behind obstacles using built-in filters.
- **Occlusion Detection**: Use a `RayCast3D` from the `AudioStreamPlayer3D` towards the listener.
- **Filter Modulation**: If the raycast is blocked, use a `Tween` to lower the `attenuation_filter_cutoff_hz` (e.g., from 20500 Hz to 1500 Hz) to create a muffled effect.
- **Room Occlusion**: Use `Area3D` with **Audio Bus Overrides** to redirect sound to a bus with a `LowPassFilter` when the source/listener enters a specific room.
### 3. Interactive-Music-Graph (Non-Linear Scoring)
Godot 4's advanced music resources for dynamic transitions.
- **Horizontal Re-sequencing**: Use `AudioStreamInteractive`. It functions as a state machine where you can define transitions between clips (e.g., "Exploration" to "Combat") that snap to the next beat or bar automatically.
- **Vertical Layering**: Use `AudioStreamSynchronized` to play multiple stems in perfect sync. Dynamically fade stem volumes (e.g., adding drums during intensity) using `set_sync_stream_volume()`.
## Performance Optimization
### Disable Far Audio
```gdscript
# Don't play sounds the player can't hear
extends AudioStreamPlayer3D
func _process(delta: float) -> void:
var listener := get_viewport().get_camera_3d()
if not listener:
return
var distance := global_position.distance_to(listener.global_position)
if distance > max_distance * 1.5: # 1.5x max range
if playing:
stop()
```
---
## Edge Cases
### Audio Doesn't Play
```gdscript
# Check:
# 1. Is stream assigned?
if not $AudioStreamPlayer.stream:
push_error("No audio stream assigned!")
# 2. Is bus muted?
var bus_idx := AudioServer.get_bus_index($AudioStreamPlayer.bus)
if AudioServer.is_bus_mute(bus_idx):
print("Bus is muted!")
# 3. Is volume too low?
if $AudioStreamPlayer.volume_db < -60:
print("Volume too quiet (< -60 dB)")
```
---
## Decision Matrix: Which AudioStreamPlayer?
| Feature | AudioStreamPlayer | AudioStreamPlayer2D | AudioStreamPlayer3D |
|---------|------------------|---------------------|---------------------|
| **Spatial** | ❌ Global | ✅ 2D panning | ✅ 3D positioning |
| **Doppler** | ❌ | ❌ | ✅ |
| **Attenuation** | ❌ | ✅ Distance-based | ✅ 3D falloff |
| **Reverb send** | ❌ | ❌ | ✅ |
| **Use for** | Music, UI | 2D games | 3D games |
| **Performance** | Fastest | Medium | Slowest |
## Advanced Audio Patterns
### 1. High-Precision Subtitle Sync
To prevent subtitle drift in long audio tracks, don't rely on simple timers.
- **Formula**: `Position = get_playback_position() + get_time_since_last_mix() - get_output_latency()`.
- **Implementation**: Poll this value in `_process` and compare against a timestamped subtitle track.
### 2. Vertical Music Layering
Use `AudioStreamSynchronized` to keep multiple stems (drums, bass, melodies) perfectly aligned.
- **Dynamic Mix**: Use `set_sync_stream_volume(index, db)` to fade layers in/out based on combat intensity or exploration progress.
- **Tweening**: Always use a `Tween` to interpolate volume changes over 1-2 seconds for a natural transition.
## Reference
- Master Skill: [godot-master](../godot-master/SKILL.md)