The 808 and 1020 capture stereo audio but omnidirectional.
The 1520 uses two second generation HAAC rich recording microphones in pairs for each audio channel. The processing combined with suitable acoustic implementation of the microphones in pairs creates a directional cardioid type stereo recording pattern. This means the 1520 records sounds in front of the camera and attenuates sound from other directions, with the sound in front being up to twice as loud as the back.
Improved clarity from audio in front
Improved accuracy and resolution from stereo image
Improved localisation of sound around the camera and creating a greater sense of depth and immersiveness
Direction free, full bandwidth stereo recording.
Quite nicely however, Nokia gives you the option to switch between omnidirectional and directional as there may be situations which omnidirectional is preferable too.
The quad microphones also allow for even better noise reduction too.
This should really have a catchy marketable name. Include something that emphasises the potential 3D surround sounding recording.