Audio Design skill

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 and hit a loudness target. Keep true peaks at or below -1 dBTP and measure integrated loudness over a representative play session with an ITU-R BS.1770 meter. Sony's ASWG-R001 recommendation, the usual reference, is -24 LUFS (±2) for console/PC played on TVs and speakers and -18 LUFS (±2) for handheld/mobile. Music-streaming targets such as -14 LUFS are not game targets.
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

Snippets are Godot 4.7 GDScript; the Unity 6.3 LTS and middleware equivalents are noted under each one.

1. Bus routing and slider-to-gain mapping

# 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 bus gain. Squaring the slider first spreads the
# audible change over the whole travel; a raw linear-amplitude slider puts most of
# the change in the bottom fifth.
func set_bus_volume(bus_name: StringName, slider01: float) -> void:
    var idx := AudioServer.get_bus_index(bus_name)
    var gain := clampf(slider01, 0.0, 1.0)
    AudioServer.set_bus_mute(idx, gain <= 0.0)             # true silence at 0
    AudioServer.set_bus_volume_linear(idx, gain * gain)    # = set_bus_volume_db(idx, linear_to_db(gain * gain))
# WRONG: AudioServer.set_bus_volume_db(idx, slider01): "0.5" is +0.5 dB (no audible
# change) and 0 is 0 dB (full volume).

Unity 6.3 LTS: expose the group's Volume as a mixer parameter, then mixer.SetFloat("MusicVolume", 20f * Mathf.Log10(Mathf.Max(gain * gain, 0.0001f))) (the mixer floor is -80 dB). An AudioSource whose Output group is empty plays outside your mixer groups, so no category slider or snapshot affects it: route every source.

2. Ducking via sidechain (music dips under voice)

A compressor on the music bus, keyed by the voice bus, lowers the music while dialogue plays and releases afterwards. Starting values: threshold about -30 dB on the voice signal, ratio 4:1 to 8:1, attack as fast as the effect allows (up to ~10 ms), release 300-500 ms.

# Godot 4.7: AudioEffectCompressor reads its sidechain bus for threshold detection.
func _ready() -> void:
    var duck := AudioEffectCompressor.new()
    duck.sidechain = &"Voice"      # the bus that triggers the dip
    duck.threshold = -30.0         # dB, range -60..0
    duck.ratio = 8.0               # range 1..48
    duck.attack_us = 2000.0        # MICROseconds, range 20..2000 (2 ms is the maximum)
    duck.release_ms = 400.0        # milliseconds, range 20..2000
    AudioServer.add_bus_effect(AudioServer.get_bus_index(&"Music"), duck)

# No-compressor alternative: tween a dedicated "MusicDuck" bus that sits between
# Music and Master, so ducking never overwrites the player's Music slider.
func duck_music(active: bool) -> void:
    var idx := AudioServer.get_bus_index(&"MusicDuck")
    var from := AudioServer.get_bus_volume_db(idx)
    var to := -12.0 if active else 0.0
    create_tween().tween_method(
        func(db: float) -> void: AudioServer.set_bus_volume_db(idx, db), from, to, 0.25)

Unity 6.3 LTS: add a Duck Volume effect to the Music group and a Send effect on the Voice group targeting it. FMOD Studio and Wwise have sidechain/auto-ducking on buses; prefer those over script tweens when the project already uses middleware.

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

# Godot 4.7: AudioStreamRandomizer picks a take (no immediate repeats by default)
# and randomizes pitch and volume on every play. No per-shot node allocation.
func make_footsteps(samples: Array[AudioStream]) -> void:
    var rnd := AudioStreamRandomizer.new()
    for s in samples:
        rnd.add_stream(-1, s)                 # -1 appends; optional third arg = weight
    rnd.random_pitch_semitones = 1.0          # up to +/-1 semitone (about 6%)
    rnd.random_volume_offset_db = 2.0         # up to +/-2 dB
    $Footsteps.stream = rnd
    $Footsteps.max_polyphony = 4              # overlapping steps without new players

Unity 6.3 LTS has no built-in randomizer: keep an array of clips, pick one that differs from the last, set pitch in a small range, and call PlayOneShot on a pooled AudioSource.

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
const SECONDS_PER_BEAT := 60.0 / BPM

# What the player HEARS now: playback position, plus time since the last mix
# (the position only updates once per mixed chunk), minus output latency.
func song_time() -> float:
    return ($Music.get_playback_position() + AudioServer.get_time_since_last_mix()
            - AudioServer.get_output_latency())

func current_beat() -> int:
    return floori(song_time() / SECONDS_PER_BEAT)  # negative means beat 0 is not audible yet

# Quantize an action to the NEXT beat boundary instead of firing immediately.
func time_until_next_beat() -> float:
    var time := song_time()
    if time < 0.0:
        return -time                             # pre-roll: wait for the first audible beat
    return SECONDS_PER_BEAT - fposmod(time, SECONDS_PER_BEAT)
# At an exact non-negative beat boundary, NEXT means one full beat later.

Unity 6.3 LTS: read AudioSettings.dspTime and schedule with AudioSource.PlayScheduled(dspTime) for sample-accurate starts.

Pitfalls

• Treating slider values as dB. Map 0..1 to gain (linear_to_db, or set_bus_volume_linear) and back with db_to_linear. A raw linear-amplitude slider sounds almost unchanged over most of its travel and drops off at the bottom; squaring (or cubing) the slider before conversion evens it out.
• Per-clip volume instead of buses makes a global balance pass impossible and bloats save/settings. Mix on buses.
• Sources that bypass the mix. A Unity AudioSource with no Output group, or a Godot player left on Master, ignores the category sliders. Route everything.
• 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.
• Ducking that fights the volume slider. Tweening the Music bus back to 0 dB overwrites the player's setting. Duck a separate bus, or use the compressor.
• 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, add the time since the last mix, and subtract output latency.
• Unbounded one-shot players: spawning AudioStreamPlayers without freeing them leaks. Use max_polyphony/AudioStreamRandomizer, free on finished, or pool them.

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.