SoundBubble (free) (org.plumbsoftware.soundbubblefree) on Google Play
Free fully functional demo - try before you buy.Create pleasing natural soundscapes for blocking irritating extraneous noise, and / or to help with concentration, meditation, relaxation and sleep. Can also be used to mask mild Tinnitus. - High quality immersive 3D stereo sound (use headphones or good quality loudspeakers for best results). - Infinitely variable output that never repeats. - No media streaming - works offline. - Once downloaded no internet connection required. - Easy to use and configure. - Change background, add or remove foreground sounds. - Individual volume, balance, frequency or interval controls. - Create save and duplicate presets. - Includes White, Pink, Brown Noise generator. - Employs Android background service.You could even turn an old unused Android mobile into a permanent soundscape generator.