Fix: Normalize sound effect loudness (#3738)

mirror of https://github.com/openfrontio/OpenFrontIO.git synced 2026-06-21 06:10:42 +00:00

## Summary
- Normalises all 20 SFX files to -22 LUFS with true peak ≤ -2 dBFS
- Collapses a ~20dB loudness spread (hydrogen-hit at -14.94 LUFS vs
sam-hit at -34.56 LUFS) into ~2dB
- Previously jarring hits (hydrogen, atom, MIRV) pulled down 6–8dB;
previously-quiet hits (sam-hit, message) brought up to match
- Short clips (`click.mp3`, `ka-ching.mp3`) too short for EBU R128 — got
a flat -6dB trim

## Why
Addresses #3728, specifically the "*WAY too loud*" feedback. Loudest
clips were peaking within ~1.5dB of clipping.

Does **not** change overlap/stacking — per discussion in #3728 and
#3394, the 8-concurrent-sound channel limit is retained intentionally.
At -22 LUFS, multiple overlapping events remain comfortable.

## Before / after (key files)

| Effect | Before (LUFS / TP dBFS) | After (LUFS / TP dBFS) | Δ |
|---|---|---|---|
| hydrogen-hit | -14.94 / -1.62 | -22.52 / -9.10 | −7.6 dB |
| atom-launch | -17.16 / -1.53 | -23.84 / -8.14 | −6.7 dB |
| hydrogen-launch | -16.15 / -1.92 | -23.65 / -9.37 | −7.5 dB |
| mirv-launch | -19.08 / -3.17 | -24.80 / -9.80 | −5.7 dB |
| sam-hit | -34.56 / -10.77 | -23.97 / -1.98 | +10.6 dB (raised up) |
| message | -29.47 / -24.46 | -21.97 / -17.00 | +7.5 dB (raised up) |

All durations unchanged (verified with `ffprobe`). All true peaks stay
below -1 dBFS — no clipping.

## How
Applied with ffmpeg's EBU R128 `loudnorm` filter:
```
ffmpeg -i in.mp3 -af "loudnorm=I=-22:TP=-2:LRA=7" -codec:a libmp3lame -q:a 2 out.mp3
```

Files shorter than the 1-second EBU R128 window (`click.mp3` 153ms,
`ka-ching.mp3` 586ms) used \`-af volume=-6dB\` instead.

## Test plan
- [x] Singleplayer: launch atom / hydrogen / MIRV nukes, verify
detonations are satisfying but not startling
- [x] Build city / port / warship / SAM, verify construction sounds sit
naturally in the mix
- [x] Trigger alliance suggest/break, verify they match loudness of
build sounds
- [x] Trigger many simultaneous events, verify the mix is comfortable
- [x] Verify no audio truncation / glitching / clipping

Addresses #3728

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