Acoustics: lying snow absorbs sound (snow-covered surfaces deaden reflections and reverb) #930

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opened 2026-10-21 23:01:24 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-21 23:01:24 +00:00

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Part of the room acoustics work (#683, #857, #858, #897) and the weather system (#783).

Snow is one of the best natural sound absorbers: fresh snow takes in most of the energy that hits it, especially mid and high frequencies. Snowy landscapes therefore sound noticeably quiet and "dead": little reflection, short reverb, muffled distant sounds. Today the acoustics rays see the surface underneath (terrain, prims) with its usual hardness, so a snow-covered courtyard sounds exactly like a bare one.

Proposal

Snow-covered surfaces get a snow material. When an acoustics ray (room rays, bounce rays, per-source rooms, early-gain sets, diffraction probes) hits a surface, look up the lying snow depth at the hit point from the weather snow maps (the inner grid / outer ring the renderer already keeps). Above a small depth (a few cm), blend the hit's absorption toward snow's, by depth: a thin dusting barely changes anything; 10 cm or more is fully snow.
- Band absorption for fresh snow: low ~0.45, mid ~0.75, high ~0.9.
- Packed and old snow (footprint compaction, tracks, melting) is harder: lower absorption.
- Wet / slushy snow is between snow and water.
Surfaces only reached through snow cover: for example a wall under a drift, or a roof with snow on it. These use the snow material on their top faces only; walls stay as they are unless snow actually lies on them.
Falling snow: heavy snowfall slightly dampens high frequencies over distance. Optionally add a small extra air-absorption term per band while it's snowing heavily, scaled by intensity. Keep it subtle.
Effect on outputs:
- shorter reverb (T60) and lower wet level outdoors in snow;
- weaker early reflections off the ground;
- less early-gain boost from snowy floors;
- the #897 boundary bass is reduced near snow-covered surfaces (snow is soft);
- weather audio unchanged, apart from its own existing rules.
Cost: one snow-map lookup per ray hit, only while snow lies in the area. No new rays.
No snow: no effect; acoustics behave exactly as today. When the weather master switch is off, snow is cleared, so there's no effect.
Setting: a strength control (0 = ignore snow), default on.

Test

A snowy open field versus the same field clear: snowy should sound drier and quieter, with almost no reverb.
A courtyard with snow on the ground but bare walls: shorter decay than when clear, but the walls still reflect.
Footprint-packed paths versus fresh snow: a slight difference.
Heavy snowfall: distant sounds slightly duller at high frequencies.

Part of the room acoustics work (#683, #857, #858, #897) and the weather system (#783). Snow is one of the best natural sound absorbers: fresh snow takes in most of the energy that hits it, especially mid and high frequencies. Snowy landscapes therefore sound noticeably quiet and "dead": little reflection, short reverb, muffled distant sounds. Today the acoustics rays see the surface underneath (terrain, prims) with its usual hardness, so a snow-covered courtyard sounds exactly like a bare one. ## Proposal - **Snow-covered surfaces get a snow material.** When an acoustics ray (room rays, bounce rays, per-source rooms, early-gain sets, diffraction probes) hits a surface, look up the lying snow depth at the hit point from the weather snow maps (the inner grid / outer ring the renderer already keeps). Above a small depth (a few cm), blend the hit's absorption toward snow's, by depth: a thin dusting barely changes anything; 10 cm or more is fully snow. - **Band absorption for fresh snow:** low ~0.45, mid ~0.75, high ~0.9. - **Packed and old snow** (footprint compaction, tracks, melting) is harder: lower absorption. - **Wet / slushy snow** is between snow and water. - **Surfaces only reached through snow cover:** for example a wall under a drift, or a roof with snow on it. These use the snow material on their top faces only; walls stay as they are unless snow actually lies on them. - **Falling snow:** heavy snowfall slightly dampens high frequencies over distance. Optionally add a small extra air-absorption term per band while it's snowing heavily, scaled by intensity. Keep it subtle. - **Effect on outputs:** - shorter reverb (T60) and lower wet level outdoors in snow; - weaker early reflections off the ground; - less early-gain boost from snowy floors; - the #897 boundary bass is reduced near snow-covered surfaces (snow is soft); - weather audio unchanged, apart from its own existing rules. - **Cost:** one snow-map lookup per ray hit, only while snow lies in the area. No new rays. - **No snow:** no effect; acoustics behave exactly as today. When the weather master switch is off, snow is cleared, so there's no effect. - **Setting:** a strength control (0 = ignore snow), default on. ## Test - A snowy open field versus the same field clear: snowy should sound drier and quieter, with almost no reverb. - A courtyard with snow on the ground but bare walls: shorter decay than when clear, but the walls still reflect. - Footprint-packed paths versus fresh snow: a slight difference. - Heavy snowfall: distant sounds slightly duller at high frequencies.

sky_line added the

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2026-10-21 23:01:24 +00:00

sky_line added this to the Slipstream project

2026-10-21 23:01:24 +00:00

sky_line referenced this issue from a commit

2026-10-22 08:20:13 +00:00

#930: acoustics -- lying snow absorbs sound

sky_line referenced this issue from a commit

2026-10-22 08:20:13 +00:00

#930: acoustics snow -- inner grid column read a full texel off the hit (wall faces leave their own texel)