Sony claims the MDR-NC500Ds are the world's first digital noise-cancelling headphones. By this, Sony means they're the first to have an on-board digital signal processor that intelligently works out which background noises are the most annoying and then works to get rid of them. All this electronic jiggery-pokery comes at a price, however, as the cans will set you back a not-inconsiderable sum of around £260. That's more expensive than a new 16GB iPod touch.
As these headphones have an over-the-ear design, they're relatively large. Despite their size, however, they actually feel very light -- Sony has managed to keep the weight down by using magnesium and aluminium alloys in their construction. Unlike most over-the-ear models, the ear pieces don't actually sit on your ears, but rather completely envelop them and, as a result, they are much more comfortable during prolonged use.
The standard method for noise cancellation is simply to use small microphones on the outside of the ear pieces to capture external sound. This is then inverted and fed into the headphone drivers. The system used here, however, is more complex. The external sound is still captured using microphones on the ear pieces, but it's then analysed by a digital signal processor which intelligently works out which are the most annoying noises and removes them accordingly. It's clever stuff, but how well does it work?
Switching on the noise cancellation in a normal room is rather disconcerting, as it so severely cuts out background sound that you're left feeling isolated from the world. The effect isn't so startling in a much noisier environment. For example, on London Underground, although the headphones cut out a lot of background noise, some was still audible when we were listening to music at a low volume. We have to say, however, that the noise-cancelling system is still probably the best we've experienced.