Works very well

I was excited by the possibilities of version 1.0, but some audio bugs prevented me from being able to fully use the program.
They have all been resolved in version 1.1, and now it performs quite well. Im using it now, in fact, while I sit in a noisy coffee shop.
Its difficult to describe the way it works; it masks exterior sound by generating, on the fly, audio that is less distracting. It does this by sampling the ambient audio with the microphone attached to your headphones. (obviously, iPhone-type headphones, with a mic, are required). It has a number of modules, each of which create different-sounding masking. I find the Rain Masker one the most useful, but the one called Noise Masker is the most clever. Noise Masker plays back the audio it hears in a softened, distorted manner, with lots of echos, which gives the effect of sitting on an upper balcony of a huge marble train station, listening to all the people coming and going down below.

Dan Walkowski about SoundCurtain