Spatial Audio

HYDRA includes four components for positional and environmental audio. They all work from Unity's physics layer — attach them to GameObjects with Colliders and they react automatically to the player entering and leaving.

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AudioBlendZone

Crossfades between two tracks based on where the listener is within a trigger collider. As the player walks from one side to the other, the mix shifts continuously from Track A to Track B.

Add AudioBlendZone to any GameObject. It requires a trigger Collider on the same object.

Field	Description
Track A	Track audible when blend = 0 (start of the blend axis).
Track B	Track audible when blend = 1 (end of the blend axis).
Blend Axis	Local-space direction along which the blend is calculated. Default: Vector3.right.
Listener	The transform to track (e.g. the player root). Falls back to any object tagged Player, then Camera.main.
Entry Fade Duration	Fade-in duration applied when the listener enters the zone.

How blending works

HYDRA projects the listener's local position onto the blend axis and normalises it against the collider's local bounds. The result is a 0–1 factor:

• 0 → only Track A is audible.
• 0.5 → both tracks play at equal volume.
• 1 → only Track B is audible.

Both tracks are started when the listener enters the trigger. Volume is updated every frame.

Blend axis orientation

For a zone where the music changes as you walk north, set Blend Axis to (0, 0, 1) (local forward). For east-to-west, use (1, 0, 0). The axis is in the zone's local space, so you can rotate the GameObject to orient the transition in any direction.

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AudioAcousticZone

Swaps the active AudioMixerSnapshot when the listener enters or exits a trigger. Use this to change reverb profiles between acoustic environments — open air, indoors, cave, corridor.

Add AudioAcousticZone to any GameObject with a trigger Collider.

Field	Description
Inside Snapshot	Snapshot to apply when the listener enters.
Outside Snapshot	Snapshot to restore when the listener exits.
Enter Transition Time	Seconds to blend between snapshots on enter.
Exit Transition Time	Seconds to blend between snapshots on exit.
Listener	Transform to track. Falls back to objects tagged Player.

Mixer Snapshots

Create snapshots in your Unity AudioMixer asset and expose them. Each snapshot stores a full set of mixer parameter values — reverb send levels, EQ, compressor settings, whatever you like.

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AudioOcclusionController

Muffles audio through walls in real time using a raycast from the sound source to the listener. As walls block the ray, an AudioLowPassFilter is tightened on every stem source to simulate the sound being heard through geometry.

Add AudioOcclusionController to any GameObject that also has an AudioTrackPlayer. The component is automatically associated via RequireComponent.

Field	Description
Listener	The listener Transform. Falls back to Camera.main.
Occlusion Layers	LayerMask for geometry that blocks audio.
Max Hits	Maximum wall hits counted per ray. More hits = stronger occlusion.
Update Interval	Seconds between raycasts. Lower = more responsive; higher = cheaper.
Occluded Cutoff Hz	Low-pass filter cutoff when fully occluded. Typical: 600–1200 Hz.
Occluded Resonance Q	Resonance strength when fully occluded. Higher = more pronounced muffling.
Smooth Time	Seconds to blend between open and occluded states (SmoothDamp).

The component creates an AudioLowPassFilter on each stem's AudioSource automatically at startup — you don't need to add them manually.

Performance

Set Update Interval to 0.1 or higher for distant or unimportant sources. The default 0.05 (20 updates/second) is appropriate for player-adjacent sources.

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AudioDistanceControl

Scales individual stem volumes based on distance between a target and the player. Unlike Unity's built-in 3D audio rolloff (which works on the AudioSource), this operates per-stem — so different layers of the same track can fade at different distances.

Add AudioDistanceControl to any scene GameObject.

Field	Description
Target	The sound source position (e.g. a speaker in the world).
Player	The listener's Transform.
Audio Track	The AudioTrackPlayer whose stems are controlled.
Stem Distances	Per-stem distance curve definition.

Each Stem Distance entry has:

Field	Description
Stem ID	Must match a stem ID in the track.
Max Volume Distance	Distance at which the stem plays at full volume.
No Volume Distance	Distance at which the stem is completely silent.

Volume is linearly interpolated between the two distances.

Stem "bass":   Max Volume: 5m → No Volume: 20m
Stem "treble": Max Volume: 2m → No Volume: 10m

Result: bass carries further, treble drops off faster — as in real acoustics.