I was recently working in an anechoic chamber for a few days and the ambience in there (actually, the lack of any) really got me thinking about ambient sounds. Anechoic chambers aren't just silent—it's the absence of any return energy that makes them so unnatural, and after a few hours, downright uncomfortable. You become aware of sounds your own body makes, especially your heart beat in your ears. It’s such an unusual space because it doesn’t really occur in the natural world. Standing on the sandy plain of a desert comes close, but even there, one would hear the movement of air over the ground, and distant ambience. A true anechoic experience almost never happens in our daily lives.