A sound played backwards: it swells from nothing to full in one breath and is cut off at the top, for undoing an action, stepping back, or rewinding a value. The reverse envelope is the point — a normal sweep fades out, this one refuses to. Use it for undo, revert, back, or restoring a deleted row.
body: band-passed white noise, centre 900 Hz -> 3200 Hz over 180 ms (Q 1.1), amplitude (t/0.18)^3 — an exponential swell from nothing, then cut to silence in 5 ms at 180 ms (the reverse of a decay) flutter: triangle 420 Hz -> 760 Hz at 25% level, amplitude-modulated at 25 Hz (0.55-1.0 depth) — the clatter of tape spooling back tick: 4 ms of high-passed noise at 2600 Hz at 185 ms, level 0.10 (the spool arriving) seam: none, single shot, buffer 0.22 s