Variation

Sounding alive means never sounding mechanical. HYDRA provides two dedicated components for ambient and one-shot variation, plus the stochastic clip system baked into stems.

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AudioScatterer

AudioScatterer randomly spawns one-shot sounds around the listener at a configurable rate. Use it for ambient layers — birds, wind gusts, distant footsteps, environmental chatter. Each sound is a temporary AudioSource that is destroyed when it finishes playing.

Add AudioScatterer to any scene GameObject.

Field	Description
Clips	Pool of AudioClips. One is picked at random per spawn event (uniform).
Listener	The transform at the centre of the spawn area. Falls back to Camera.main.
Spawn Radius	Radius in metres around the listener within which sounds may spawn (XZ plane).
Min Spawn Distance	Minimum metres between consecutive spawn positions. Prevents clustering.
Events Per Minute	Average number of spawn events per minute. The actual interval varies ±25% to avoid a metronomic feel.
Base Volume	Playback volume (0–1).
Volume Variation	Symmetric random volume offset per spawn (e.g. 0.1 = ±0.1).
Base Pitch	Base pitch multiplier.
Pitch Variation	Symmetric random pitch offset per spawn.
Audio Group	Routes spawned sounds through this mixer group. Optional.

The scatterer runs as long as the component is enabled. Disable it to pause all spawning.

Example — forest ambience

AudioScatterer: Forest Birds
  Clips: [crow_caw, robin_chirp, jay_call, distant_coo]
  Spawn Radius: 30m
  Min Spawn Distance: 5m
  Events Per Minute: 8
  Base Volume: 0.7
  Volume Variation: 0.15
  Base Pitch: 1.0
  Pitch Variation: 0.08
  Audio Group: Ambience

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AudioImpulse

AudioImpulse is for one-shot reactive sounds — footsteps, button clicks, impact hits, anything that fires in response to a game event. It pre-pools AudioSources and supports weighted clip selection with history suppression and a minimum interval rate limiter.

Add AudioImpulse to any scene GameObject. Call Play() from any script or animation event.

Field	Description
Clip	Fallback single clip when no weighted clips are provided.
Weighted Clips	Pool of WeightedAudioClip entries (clip + weight). When populated, overrides the single clip.
History Size	How many recent clip indices to suppress before they can repeat.
Pitch Range	x = min pitch, y = max pitch. Randomised per play.
Volume Range	x = min volume, y = max volume. Randomised per play.
Min Interval	Seconds of cooldown between calls. Calls within this window are silently ignored. Prevents double-hits.
Audio Group	Mixer group for all pooled sources. Optional.
Pool Size	Number of AudioSources pre-created. Default: 4. Set higher for rapid-fire sounds.

// Wire this up in your footstep system, OnCollisionEnter, or an Animation Event
[SerializeField] AudioImpulse footstepImpulse;

void OnFootstep()
{
    footstepImpulse.Play();
}

Pool sizing

For footsteps at a fast run, set pool size to 4–6. For occasional impact hits, 2 is usually fine. The impulse silently skips if the pool is exhausted (all sources are still playing).

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Stochastic clips on stems

For music stems that need variation — e.g. a percussion hit that sounds slightly different each bar — use Weighted Variation directly on the AudioStem in your AudioTrack asset.

See Audio Tracks — Clip Variation for full details.

The key difference from AudioImpulse:

• AudioImpulse is for SFX triggered by game events.
• Stem weighted variation is for music/ambience clips that are re-picked automatically on each Play of a non-looped stem.

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Comparing the variation tools

Tool	Best for	Spatial	Mixer routing
AudioScatterer	Ambient ambient sounds spread in space	Yes (XZ scatter)	Via AudioGroup
AudioImpulse	One-shot reactive SFX at a fixed position	No (pooled at parent)	Via AudioGroup
Stem weighted clips	Music / ambience clip variation on a track	Inherits from track	Inherits from AudioGroup