A bubble, a curve,
and a default that must not travel.

Anywhere at or inside Min Distance the gain is exactly 1.0 — full volume, no fade. Verified at 0 metres, at 4.9 on a min of 5, and at 5 exactly. Only past that boundary does any curve begin.

So Min Distance is not a fade-in point or a minimum audible range. It is the radius of a bubble of full volume around the source, and it is also the number every model measures its falloff from.

The two Inverse models are ratios built from Min Distance and Rolloff. Max Distance is simply not in the expression, so moving it changes nothing — measured, the gain at 50 metres was 0.0200 with a Max of 20 and 0.0200 with a Max of 5000.

Linear and Logarithmic work the other way round: they map the distance onto the range between Min and Max, so Max Distance is what shapes them. Change it and the gain at a fixed distance moves immediately.

Inverse is a ratio, so it asymptotes: it gets arbitrarily quiet and never actually arrives at zero. In practice that is inaudible, but it is not silence, and a sound that is technically still playing across the whole map is a sound the engine is still mixing.

Linear reaches exactly zero at Max Distance and stays there — verified at 100 metres on a max of 100, and at 100 kilometres. If you need a guarantee that something cannot be heard past a boundary, that guarantee only exists on Linear.

The model name itself is matched loosely — case-insensitively, and by looking for a substring. That has one consequence worth knowing: a model name the tool does not recognise silently becomes Inverse. Verified, a clip set to "Bouncy Castle" produced exactly the Inverse curve. And "none" is treated as Disabled, alongside "Disabled" itself.

So a typo in a model name is not an error. It is a quiet change of curve, and it will look like whatever Inverse looks like.

This is not a compression Echo invented. It is the shape the game already uses: a sound holds a list of clips and picks between them when something triggers it. A bank is that idea, authored.

So the mental model to carry is not "a bank groups my sounds" but "a bank is my sound, and the variants are the ways it can come out". Once a clip is in a bank it stops being a thing the game can trigger on its own — verified, the variants did not appear as sounds of their own in the bundle.

Tune one variant to a pitch of 1.3 and a volume of 0.4, put it in a bank, and export: the bank's values are what ship. Echo does not do this quietly — the export names the variant and lists exactly which of its settings were replaced, verified.

The variance controls are where a bank's own expressiveness lives, and they map cleanly: ±0.05 pitch variance becomes the range 0.95 to 1.05. That is the same statement written two ways, which is why this one survives intact.

All three are reported, and all three mean a sound you authored does not reach the game. The name collision is the one to watch, because it is the only one that happens while everything looks healthy — both objects exist, both are visible in the tool, and one of them silently does not ship.

Banks are referenced internally by id rather than by name, so renaming a clip does not break the bank it belongs to. Names matter at the boundary, not inside the project.

Verified: a project with a bus called Ambience, a clip routed to it, and an event named amb_start exported one sound — and the notes named the bus, the event, the clip's routing and its loop flag as things that could not be carried. The game's sound definition has no bus, no reverb, no routing and no event list.

That is worth stating plainly rather than treating as a defect. Echo tells you what it could not carry, once for each thing, by name. Most tools in a position to lose something quietly do lose it quietly; this one is built to say so, and reading those notes after an export is the fastest way to learn where the ceiling is.

The lane searches inside a mod root and nowhere else. A file written outside one is invisible to it however correct its contents are — and because the export reported success and produced a real file, there is nothing to notice.

This is why the bundle export refuses to run without a mod folder open, rather than falling back to somewhere convenient. A bundle that cannot be inside a mod has no reason to exist, so it fails early and says why.

Copying Echo's own default across would look harmless and would be a real bug. Every clip whose author never opened the spatial panel would arrive carrying MaxDistance 100 against a game that assumes 500 — quietly cutting the audible range fivefold on every sound nobody had an opinion about.

So the rule the export applies is did a human move this? An untouched value is treated as no opinion and the game's own default is left in place. A value you actually changed travels exactly — verified, a Max Distance set to 30 exported as 30.

The right-hand column is long, and Echo names every item in it, once each, by the clip or bank it belonged to. That is unusual and deliberate. A tool in this position can drop what it cannot carry in silence, or mangle it into a field that means something else; this one reports it.

Which makes the export notes the fastest documentation of the boundary that exists. Export once, read what it says it could not carry, and you have learned the shape of what the game accepts more quickly than any page could tell you — including this one.