/audio-design

name: audio-design
description: >
  Implement game audio practice — bus/mixer architecture and gain in decibels,
  ducking (sidechain), adaptive/dynamic music via layering and re-sequencing,
  SFX variation, and beat synchronization. Engine-neutral. Use when the user
  mentions audio mixing, audio buses, adaptive/dynamic music, ducking, SFX
  variation, music layers, or syncing gameplay to the beat.

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

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