audio-design

Audio design

Game audio is a mixing graph plus a music system. Route every sound through a small set of buses so you can balance and process groups; make music react to play through layering and re-sequencing rather than looping one track. This skill teaches the portable practice; bind it to godot-audio, Unity's AudioMixer, or middleware (FMOD/Wwise) for concrete APIs.

When to use

• Use to design a bus/mixer layout, set group volumes, and apply effects (reverb, compression, EQ) to groups of sounds.
• Use to duck music/ambience under dialogue or impacts (sidechain).
• Use to build adaptive music that responds to combat/exploration intensity.
• Use to add SFX variation (pitch/sample randomization) and sync events to a beat.

When not to use: for the engine's concrete audio nodes/streams, use godot-audio or the engine's audio skill. Loading/streaming and asset import are engine concerns. For UI sliders that drive bus volume, see the engine UI skill.

Core workflow

1. Lay out buses, not per-sound volume. A typical tree: Master ← {Music, SFX, Ambience, UI, Voice}. Everything plays into a bus; the player's settings sliders map to bus volumes. Never set hundreds of clip volumes by hand.
2. Work in decibels, not linear. Perceived loudness is logarithmic. Volume controls and automation should operate in dB; convert only at the edges.
3. Leave headroom. Mix so the Master peaks below 0 dBFS (aim for a target loudness, e.g. around -14 to -16 LUFS for many games) to avoid clipping.
4. Duck competing sources with a sidechain compressor (or volume automation): when voice/important SFX plays, the music bus dips, then recovers.
5. Make music adaptive via vertical layering (stems faded in/out) and/or horizontal re-sequencing (swap segments at musical boundaries). See the reference.
6. Vary repeated SFX with small random pitch/volume offsets and sample pools so footsteps and hits don't sound robotic.
7. Verify on real output. Listen on headphones and speakers; check that the mix balances, ducking is audible but not pumping, and music transitions land on the beat — never assume from the editor meters alone.

Patterns

1. Bus routing and dB gain

# Route sounds to named buses; control GROUPS, not individual clips.
sfx_player.bus = "SFX"
music_player.bus = "Music"

# Map a 0..1 settings slider to decibels (linear_to_db), the perceptual unit.
func set_bus_volume(bus_name: String, slider01: float) -> void:
    var idx := AudioServer.get_bus_index(bus_name)
    var db := linear_to_db(clamp(slider01, 0.0001, 1.0))   # 0 -> silence, 1 -> 0 dB
    AudioServer.set_bus_volume_db(idx, db)
# RIGHT: slider -> dB via linear_to_db. WRONG: assigning slider01 straight as dB
# (a "0.5" would be only +0.5 dB — almost no change — and 0 would be 0 dB, full).

2. Ducking via sidechain (music dips under voice)

# A compressor on the MUSIC bus, keyed by the VOICE bus, lowers music while
# dialogue plays, then releases. This is "sidechain ducking".
# Setup (engine-specific): add a compressor effect to the Music bus and set its
# sidechain to the Voice bus. Then tune:
#   threshold: level on Voice that triggers ducking (e.g. -30 dB)
#   ratio:     how hard to duck (e.g. 8:1 for a clear dip)
#   attack:    fast (~10 ms) so music gets out of the way promptly
#   release:   slow (~300-500 ms) so it recovers smoothly, not pumping
# No-middleware alternative: tween the Music bus volume down on voice start and
# back up on voice end.
func duck_music(active: bool) -> void:
    var target_db := -12.0 if active else 0.0
    create_tween().tween_method(
        func(v): set_bus_volume_db("Music", v), current_music_db, target_db, 0.25)

3. SFX variation (kill the "machine gun" repeat)

# Randomize pitch slightly and pick from a sample pool so repeats feel organic.
func play_varied(samples: Array, bus := "SFX") -> void:
    var p := AudioStreamPlayer.new()
    p.stream = samples[randi() % samples.size()]   # rotate through several takes
    p.bus = bus
    p.pitch_scale = randf_range(0.94, 1.06)         # +/- ~6% pitch wobble
    add_child(p); p.play()
    p.finished.connect(p.queue_free)                # clean up one-shots

4. Beat-synced events (quantize to the music grid)

# Schedule gameplay/visuals on musical time, not frame time, so they land on beat.
const BPM := 120.0
var seconds_per_beat := 60.0 / BPM

func current_beat(playback_position_sec: float) -> int:
    return int(playback_position_sec / seconds_per_beat)

# Quantize an action to the NEXT beat boundary instead of firing immediately.
func time_until_next_beat(pos: float) -> float:
    return seconds_per_beat - fmod(pos, seconds_per_beat)
# Drive timing from the audio playback clock, which is steadier than frame delta.

Pitfalls

• Treating slider values as dB. Volume is logarithmic; map 0..1 through linear_to_db (and back with db_to_linear). A linear slider on raw amplitude feels like it does nothing until the very bottom.
• Per-clip volume instead of buses makes a global balance pass impossible and bloats save/settings. Mix on buses.
• Clipping the master. Summed sounds exceed 0 dBFS and distort. Leave headroom; put a limiter on Master as a safety net, not as the mixer.
• Pumping ducking: too-fast release or too-high ratio makes music audibly breathe. Lengthen release; lower ratio.
• Looping a single music track for the whole game feels flat. Use layers or segments that respond to state (see the reference).
• Beat sync off frame time. delta drifts; read the audio playback position for musical timing, and account for output latency.
• Unbounded one-shot players: spawning AudioStreamPlayers without freeing them leaks. Free on finished, or use a small pool.

References

• references/adaptive-music.md — vertical layering vs horizontal re-sequencing, transition timing (bars/quantize), stingers, intensity mapping, and crossfades.

Related skills

• godot-audio — buses, AudioStreamPlayer, effects, and sync-to-beat in Godot.
• input-systems — trigger audio from input actions.
• physics-tuning — collision events that drive impact SFX.
• platformer, roguelike — genres whose feel leans on audio feedback.