The thunder here is spaced way out. Strike rate is pulled down low, reverb decay a touch deeper than the rest of Sleep, so what you get is an occasional low rumble rather than anything sharp enough to wake you up. It reads like a storm passing a long way off, not one sitting overhead.
Built as sleep music for anyone who actually likes storm sounds but finds most thunder presets too abrupt for actually falling asleep to. Brown noise carries the bulk of the mix underneath, so the thunder stays a texture rather than an event, closer to weather in the distance than a soundtrack, which is exactly what makes it work as background instrumental sound for sleep instead of something startling.
Every strike is generated live rather than pulled from a fixed thunder-sample loop, so the spacing between rumbles stays irregular across the whole night instead of falling into a countable cycle.
StillTune composes endless, ever-changing music for sleep, focus and relaxation. Real melody and instruments, generated live, with no audio files. Explore more sounds.