[chad_oliver]

I'm not convinced about the ability to block out certain types of sounds (e.g. birds vs traffic), but blocking out certain frequencies should be quite possible.

Of course, there's one question the article didn't address: what proportion of sound is actually transmitted through window panes? One would expect that a whole lot of low-frequency sounds (traffic) would come through the walls too.

[radley]

I got the impression it would play bird sounds, i.e. a "zen" noise generator, not filter actual bird sounds through.

[tempestn]

That's certainly more realistic, but I think it was pretty clear in the video that the device identified the various types of sounds coming from outside, and allowed the user to independently control the amount of each to be let through.