Audio System

Audio System in Godot 4.3+

All examples target Godot 4.3+ with no deprecated APIs. GDScript is shown first, then C#.

Related skills: event-bus for decoupled audio triggers, save-load for persisting audio settings, resource-pattern for audio data containers.

1. Core Concepts

Audio Node Types

Audio Bus Architecture

Godot routes all audio through buses (like a mixing console).

Copy code
Master (always exists)
├── Music          → volume, effects for background music
├── SFX            → volume, effects for sound effects
│   ├── Footsteps  → sub-bus for fine-tuning
│   └── Weapons    → sub-bus for fine-tuning
└── UI             → volume for menu sounds

Setup: Bottom panel → Audio tab → Add buses, set names, route outputs.

Every AudioStreamPlayer has a bus property — set it to the target bus name (e.g., "SFX", "Music").

2. Basic Audio Playback

GDScript

gdscriptCopy code
extends Node2D

@onready var sfx_player: AudioStreamPlayer2D = $AudioStreamPlayer2D
@onready var music_player: AudioStreamPlayer = $MusicPlayer

func _ready() -> void:
    # Play background music (looping is set on the AudioStream resource)
    music_player.play()

func play_jump_sound() -> void:
    sfx_player.stream = preload("res://audio/sfx/jump.wav")
    sfx_player.play()

C#

csharpCopy code
using Godot;

public partial class AudioExample : Node2D
{
    private AudioStreamPlayer2D _sfxPlayer;
    private AudioStreamPlayer _musicPlayer;

    public override void _Ready()
    {
        _sfxPlayer = GetNode<AudioStreamPlayer2D>("AudioStreamPlayer2D");
        _musicPlayer = GetNode<AudioStreamPlayer>("MusicPlayer");
        _musicPlayer.Play();
    }

    public void PlayJumpSound()
    {
        _sfxPlayer.Stream = GD.Load<AudioStream>("res://audio/sfx/jump.wav");
        _sfxPlayer.Play();
    }
}

Looping Audio

Looping is configured on the AudioStream resource, not the player node:

• WAV: Import tab → Loop Mode → Forward (or Ping-Pong)
• OGG: Import tab → Loop → On, set Loop Offset
• MP3: Import tab → Loop → On

Always use OGG Vorbis for music (smaller files, good quality). Use WAV for short SFX (no decoding latency). Avoid MP3 for SFX — it adds silence at the start.

3. Audio Bus Management

Setting Volume from Code

Godot uses decibels (dB) for volume. Linear-to-dB conversion is required for sliders.

GDScript

gdscriptCopy code
# Get bus index by name
var bus_index: int = AudioServer.get_bus_index("SFX")

# Set volume in dB directly
AudioServer.set_bus_volume_db(bus_index, -6.0)  # -6 dB = ~50% perceived volume

# Convert linear (0.0–1.0) to dB — use for UI sliders
func set_bus_volume_linear(bus_name: String, linear: float) -> void:
    var index := AudioServer.get_bus_index(bus_name)
    AudioServer.set_bus_volume_db(index, linear_to_db(linear))

# Mute / unmute a bus
AudioServer.set_bus_mute(bus_index, true)

# Read current volume as linear (for displaying on a slider)
func get_bus_volume_linear(bus_name: String) -> float:
    var index := AudioServer.get_bus_index(bus_name)
    return db_to_linear(AudioServer.get_bus_volume_db(index))

C#

csharpCopy code
int busIndex = AudioServer.GetBusIndex("SFX");

// Set volume in dB
AudioServer.SetBusVolumeDb(busIndex, -6.0f);

// Linear to dB conversion for UI sliders
public void SetBusVolumeLinear(string busName, float linear)
{
    int index = AudioServer.GetBusIndex(busName);
    AudioServer.SetBusVolumeDb(index, Mathf.LinearToDb(linear));
}

// Mute / unmute
AudioServer.SetBusMute(busIndex, true);

// Read current volume as linear
public float GetBusVolumeLinear(string busName)
{
    int index = AudioServer.GetBusIndex(busName);
    return Mathf.DbToLinear(AudioServer.GetBusVolumeDb(index));
}

Audio Bus Effects

Add effects to buses in the Audio panel (bottom dock). Common effects:

Dynamic Effect Toggle

gdscriptCopy code
# Enable/disable an effect on a bus at runtime
var bus_index := AudioServer.get_bus_index("SFX")
var effect_index := 0  # First effect on the bus
AudioServer.set_bus_effect_enabled(bus_index, effect_index, true)

# Apply low-pass filter for "underwater" feel
func set_underwater(enabled: bool) -> void:
    var index := AudioServer.get_bus_index("SFX")
    # Assumes a LowPassFilter is the first effect on the SFX bus
    AudioServer.set_bus_effect_enabled(index, 0, enabled)

4. Spatial Audio (2D & 3D)

AudioStreamPlayer2D

Automatically adjusts volume and panning based on distance to the nearest AudioListener2D (or the Camera2D if no listener exists).

Copy code
Enemy (CharacterBody2D)
├── Sprite2D
└── AudioStreamPlayer2D   ← positioned at enemy's location
    bus = "SFX"
    max_distance = 1000.0
    attenuation = 1.0

Key properties:

AudioStreamPlayer3D

Same concept but in 3D. Works with AudioListener3D (or the Camera3D).

Key additional properties:

AudioListener

gdscriptCopy code
# Make a specific camera the audio listener
# 2D: add AudioListener2D as child of Camera2D, call make_current()
# 3D: add AudioListener3D as child of Camera3D, call make_current()

# By default, the current Camera2D/3D acts as the listener.
# Only add an explicit AudioListener if you need a different listening position.

csharpCopy code
// 2D spatial player
public partial class Footsteps : AudioStreamPlayer2D
{
    public override void _Ready()
    {
        Bus = "SFX";
        MaxDistance = 1000.0f;     // Pixels at which volume reaches zero
        Attenuation = 1.0f;         // Linear falloff (higher = sharper)
        MaxPolyphony = 4;           // Allow overlapping footstep sounds
    }

    public void PlayStep() => Play();
}

// 3D spatial player
public partial class EngineHum : AudioStreamPlayer3D
{
    public override void _Ready()
    {
        Bus = "SFX";
        UnitSize = 4.0f;            // Meters at which volume is 0 dB
        MaxDistance = 50.0f;
        AttenuationModel = AttenuationModelEnum.InverseDistance;
    }
}

// Custom listener — overrides the default Camera2D / Camera3D listener.
public partial class FollowCamListener : AudioListener3D
{
    public override void _Ready() => MakeCurrent();
}

⚠️ Changed in Godot 4.7: The default area_mask on AudioStreamPlayer2D/AudioStreamPlayer3D changed from 1 to 0 (disabled) — the audio_bus_override feature on Area2D/Area3D (e.g. an underwater bus) stops working for players left at the default. Set area_mask back to layer 1 to restore it; masks explicitly set to anything other than layer 1 keep working. (The migration guide says "AudioStreamPlayer", but area_mask only exists on the 2D/3D variants.) See the 4.7 migration guide.

5. Music Manager (Autoload)

Crossfade between background tracks via a singleton autoload that manages two AudioStreamPlayer nodes and tweens their volume_db. Wire a Music audio bus so the settings menu can adjust music separately.

See references/music-manager.md for the full GDScript and C# autoload (crossfade, push/pop stack, current-track query).

6. SFX Pool

Pre-instantiate a fixed pool of AudioStreamPlayer nodes; play_sfx(stream) finds the next free player and plays. Avoids per-shot instancing churn for high-volume effects (gunshots, footsteps, hits).

See references/sfx-pooling.md for the GDScript + C# pooled player and a 2D positional variant (pool of AudioStreamPlayer2D nodes that follow a target).

7. Audio Settings Integration

Wire HSliders in the settings menu to bus volumes via AudioServer.set_bus_volume_db(bus_idx, linear_to_db(value)). Persist with ConfigFile. Use the linear_to_db / db_to_linear helpers — never log-base by hand.

See references/audio-settings.md for the full settings menu wiring with persistence (GDScript + C#).

8. Interactive & Adaptive Music (Godot 4.3+)

Three stream types for adaptive music: AudioStreamPlaylist (sequenced or shuffled tracks), AudioStreamSynchronized (multiple stems played in sync — vertical layering for combat intensity), AudioStreamInteractive (clip transitions on triggers — state-driven music). Godot 4.4+ adds AudioStreamWAV.load_from_file() for runtime WAV loading.

Godot 4.7+: AudioStreamInteractive now exposes TRANSITION_TO_TIME_PREVIOUS_POSITION (TransitionToTime enum) to scripts — the destination clip resumes from its last played position if there was a previous transition from that clip, otherwise it plays from its start. Ideal for exploration ↔ combat music that picks up where it left off.

See references/interactive-music.md for the stream-type comparison, GDScript recipes, the 4.7+ resume-position transition, and the 4.4+ runtime-load example.

9. Audio Import Best Practices

Import Settings

In the Import dock (select an audio file):

• Loop: Enable for music and ambient loops
• BPM / Beat Count / Bar Beats: Set for rhythm-synced games
• Force Mono: Enable for 3D positional audio (stereo doesn't spatialize well)

Tip: Keep SFX as 16-bit WAV at 44.1kHz. Godot stores WAV uncompressed in PCK, so they play instantly with zero decode overhead. For music, OGG Vorbis at quality 6–8 is a good balance.

11. Common Pitfalls

12. Implementation Checklist

• Audio buses are set up: Master, Music, SFX (minimum)
• All AudioStreamPlayer nodes have the correct bus property assigned
• Music uses OGG Vorbis format; short SFX uses WAV
• Music player is in an autoload (survives scene changes)
• Music crossfading is implemented for smooth transitions
• SFX pool is used instead of creating new AudioStreamPlayer nodes dynamically
• Volume sliders use linear_to_db() / db_to_linear() conversion
• Near-zero slider values mute the bus (avoid linear_to_db(0.0) = -inf)
• 3D audio sources use mono audio files for proper spatialization
• Audio settings are saved and restored on game launch (ConfigFile or similar)
• Looping is configured on the AudioStream resource, not in code
• Interactive/adaptive music uses AudioStreamPlaylist, AudioStreamSynchronized, or AudioStreamInteractive (Godot 4.3+) instead of manual track-switching code