A sound FX had no space around it. The Reverb node folds the sound with an impulse response: one it makes itself, or a sound asset as the answer of a real space. It works on a voice and on a bus. - Type: Room, Hall, Cave and Plate have fixed numbers. Custom shows Decay (up to 10 s), Damping and Pre-delay. Sound shows the pick of a sound asset and Pre-delay. The rows are derived ports, the sound pick an idle param, so they only appear for their type. - The made impulse response is seeded noise per side, 60 dB down at Decay, through a low-pass closing from 20 kHz toward 500 Hz as far as Damping says. It is made once per rate, decay and damping, the last 16 are kept. - A sound as impulse response: the sound FX compilers now get the project, so a node can turn a sound asset into its file. The build key holds that file, so a cut or swapped sound builds again. The instrument compiler does the same for a Reverb inside an instrument. - The library loads that file with the voice, a sequence or before a bus builds its chain. A missing file leaves the reverb silent. - Mix blends dry and reverb and is the only number that moves while the sound plays, as the issue said. The voice rings for pre-delay plus decay, or as long as its sound. - The open point from #325 about sends on project buses is #351, not part of this. Tests: - Unit reverb (new) 4, soundfx 57 (4 new), sound-library 104 (2 new), green. - Counter-checks, each turns one test red: the impulse file not loaded with the voice, the tail without the length of the sound. - e2e 34 (melektaus-atx): ALL PASSED, 81 checks (1 new). Chrome offline: silent during the pre-delay, 35.9 dB fall over 0.6 s of a 1 s decay (36 expected), the dry half at 0.25 for mix 0.5. A sound with one sample at 0.2 s gives the impulse back 0.25 s later and nowhere else. - Gate (melektaus-atx) over the end of this series #318 to #328: CHECK EXIT 0, 267 files, 4134 tests. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>