They're also smart; as soon as you take them off they automatically pause what you're listening to; as soon as you put them back on, they automatically start it playing again. That doesn't need a special app; I tried them out with Spotify. If the autoplay doesn't work, you can tap on one of the cams to play and pause.
The audio quality is excellent. I used my standard headphone test tracks; Ragamuffin from Aerial Boundaries by Michael Hedges is a close-miked recording of acoustic guitar where you can hear his fingers sliding over the strings in fabulous detail. Teardrop from Mezzanine by Massive Attack is how I test bass response; with an average pair of headphones or speakers, you will start to hear the bass that opens the track at around four seconds. On really good audio kit at a low volume, you start to hear it about two seconds in. On the Surface Headphones, I was hearing audible palpable bass within perhaps a tenth of a second on a track that I'm used to thinking starts with silence. That's really impressive.
The left cam turns like a dial to adjust the noise reduction, the right rotates to control volume. That works very smoothly. On the noisy expo floor, the noise reduction works pretty well; I can barely hear the person talking right next to me and I can easily ignore them, all the background noise is gone, although the thumping bass from the DJ booth a few feet away is audible. There's no hissing, clipping or distortion in the sound; something I've noticed with other active noise-cancellation systems.
When I turn the noise reduction down and the ambient audio up, I can hear people talking to me. I can also hear the whole room sampled, including sound from a long way across the room where someone is playing a racing game and someone else is giving a talk. And what's when I start thinking about what else headphones could be for, other than showing off some nice audio technology that Microsoft engineers happen to be good at after creating the spatialized audio in HoloLens, and giving Microsoft another product to put the Surface name on (this isn't a bad way to slowly expand the name out beyond computers).
The Surface team considered and rejected the idea of a boom microphone which would have made the headphones look like a gaming rig -- but would have also been ideal for speech recognition and putting Cortana on your head. But the array of microphones that picks up background noise to cancel it would also do pretty well at capturing speech, so you can imagine asking Cortana on your PC for directions or to set you a timer the way you can with the Invoke, or even to dial someone on Skype.
The Surface Headphones would also work very well for Microsoft's assistive technologies like Soundscape, which has to describe the world they're walking through to those with limited vision, without blocking the sound of that world that they rely on to interpret it. It's no use telling a partially sighted person that they've reached the corner of the street and the restaurant they want is on the other side of the road if they can't listen for traffic.
Microsoft worked with Jabra and AfterShokz, but as the focus on assistive AI increases, it makes sense for Microsoft to have its own hardware -- especially as tools like live translation become available; you're going to want to be able to hear what's going on around you as well as hearing a translation of the person you're talking to.
In a way, the noise cancellation makes the Surface Headphones something of a mixed reality device; instead of overlaying holograms, they can add an extra audio track to the world around you, with as much of the background sound as you want still audible.
That's an interesting approach to the ubiquitous computing that's becoming increasingly common, where technology is not so much invisible as in the right place. And that could be useful to just about everyone.