Spatial audio: tune distance attenuation separately from HRTF direction

Separate the questions of distance and direction

Distance attenuation controls how a source's level changes as the listener moves away. Spatialization controls the directional cues in the output. A head-related transfer function, or HRTF, filters sound for binaural listening according to source direction. Steam Audio documents this directional effect separately from attenuation and propagation controls. Making a sound quieter does not, by itself, establish where it is. [1][2]

Define the listener and output path

Choose which transform represents the listener, especially when the camera and player body are separated. Verify the coordinate conventions expected by the spatializer and update orientation as well as position. Steam Audio's binaural effect takes a direction from listener to source and produces stereo output. Epic distinguishes headphone binaural rendering from loudspeaker panning. Test the actual output path rather than assuming that a stereo file and a binaural rendering path are interchangeable. [1][3]

Worked example: one gain curve, many directions

For an illustrative point source, choose full gain within 2 meters and silence at 20 meters, using gain = clamp((20 - d) / 18, 0, 1). At 2 meters the gain is 1, at 11 meters it is 0.5, and at 20 meters it is 0.

The amplitude ratio 0.5 corresponds to approximately -6.02 dB; it does not mean half the perceived loudness. This custom linear curve is a design choice, not a physical propagation claim. If the listener rotates 180 degrees without moving, the distance gain stays the same while the source-relative direction changes. A test that only checks volume would miss a reversed orientation.

Build a repeatable listening test

Use a single clearly identifiable source in a quiet scene. Walk toward it along marked distances, then circle it and rotate in place. Inspect the listener and source transforms while listening. Check left, right, front, rear and elevation, and compare the intended headphone and speaker configurations.

Add occlusion, reverberation and competing sounds separately. An occlusion query or reflection simulation solves another part of the acoustic scene; it should not obscure a basic direction bug. Check that the engine and plugin are not both applying the same distance curve. Test sources close to the listener, where small position changes can create abrupt directional changes, and define any near-field blending deliberately.

Judge information, not just realism

A technically functioning HRTF does not guarantee that every player localizes every cue accurately. Source content, playback hardware and the surrounding mix matter. Keep critical gameplay information available through additional cues when needed. Profile spatialization and propagation separately, and compare moving scenes rather than isolated static positions. A useful result preserves clear game information within the audio budget.

Sources

• [1] Binaural Effect — Valve, Steam Audio C API documentation.
• [2] Steam Audio Source — Valve, Steam Audio Unity integration documentation.
• [3] Sound Attenuation — Epic Games, Unreal Engine documentation.