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If you're into ambient noise, aSleep is probably the best app out there right now for your needs. The app offers quite a few different sounds for you to fall asleep too, plus it even has a built in timer, allowing for you to have the noise shut off if it's something that you just need to get you to sleep.
aSleep looks really nice overall presentation wise and it functions just the same. From the main screen you can change all of the settings that you could possibly need to: timer, sound on/off, sound selection, and volume. The timer and the sound selection do pull you into their own menu for you to easily scroll through what you need to setup, but there isn't much more depth than that.
The options for the sounds are broken in to categories, with each category offering several different sounds. Some of them make sense as something that you could find yourself falling asleep too, while the others are something that you hope is really on there as a joke. Either way, you can set how long you actually want them playing on your iPhone for.
The added options and the more various sound choices make this app the must have ambient noise app. Now that might not being saying much to everyone, as not everyone needs an ambient noise app. But for those who do, this would be a first page app.