If you've not played with mynoise.net, you might give it a shot. It's one person's passion project to do exactly this - more or less infinitely variable backgr

If you've not played with mynoise.net, you might give it a shot. It's one person's passion project to do exactly this - more or less infinitely variable background noise. Each soundscape has a range of samples (typically 8-10 sections), and you can adjust the levels for each section individually - or let it automatically fade stuff around. Some of the newer stuff is more algorithmically generated "infinite variation" music. I've easily put thousands of hours on the Flying Fortress option - both my kids slept better with the low background rumble of WWII bombers thundering away in their rooms (the womb is very loud, and, yes, there's a womb noise simulator too), and I love it for office background noise, though my office doesn't have other people in it (typically). I'm far, far more comfortable paying for this sort of thing, where he's gone and sampled stuff in person, than with something that's just "scraped the internet" and replicated something or another.