Nokia's head of audio technology for Lumia, Heikki Sassi, says that Nokia is the "first company to introduce four microphone directional stereo recording in a cameraphone". These directional microphones enhance the clarity of a recording by "rejecting sounds outside the direction of capture", which Nokia describes as "being the best possible way", noting that, "previously, if you wanted audio capabilities like this you would need to buy a professional video camera or external mics to do the job".
The directional microphones of the Lumia 1520 can be contrasted with the omnidirectional microphones found in the Lumia 1020, Lumia 920 and 808 PureView. Rather than recording the sound from all around you (omnidirectional), sounds are recorded from directly in front of the camera (directional), while attenuating sounds from other directions.
As a result there is a sense of direction in recording (e.g. similar to listening to someone talk while they walk around you), which is closer to how you experience audio in real life (i.e. it is more immersive).
While all four microphones are used for audio capture, audio is still encoded in two channel (i.e. stereo), with the directional element achieved by adjusting each channel appropriately. Thus, when playing back video captured by the Lumia 1520, directional effects will be most noticeable when listening on a set of headphones, or via a widely separated set of speakers.
The video embedded below demonstrated the directional audio recording by capturing the live performance from multiple angles. The audio changes subtly as the recording moves around the room, switching between the six statically positioned Nokia Lumia 1520's used in the capture process.
This live performance was captured using six Nokia Lumia 1520 prototypes. First we recorded the audio with a Nokia Lumia 1520 prototype from the center position. After that we filmed different video angles with the other five devices. Can you hear how directional mics work? Plug in your headset and enjoy! The video was edited in Adobe Premiere with no adjustments in audio quality.
View the video on YouTube and see the associated post on Nokia Conversations.
The video also serves as another example for the related Nokia Rich Recording technology. Rich Recording is the brand that Nokia uses to describe audio captured through its HAAC (High Amplitude Audio Capture) microphones, which are capable of capturing undistorted audio at a greater amplitude (up to six times the volume) and frequencies (20 Hz to 20 KHz) than is typical for the microphones found in most smartphones. This is most noticeable when recording loud noises (e.g. a rock concert), but will benefit audio capture for video shot in almost any conditions.