| It's pretty neat! Here's how it works: When you record with a single microphone, you are going to pick up a great deal of background noise. This is because the mic will pic up the person speaking AND the background noise; there's no way to differentiate the two. With two microphones, we know the following: 1) we know where the microphones are 2) we have a general idea where the persons mouth is, because we know how they hold the phone Based on that, we have a good idea of how long it should take for the sound to arrive, because the speed of sound is a fixed number. The first time I ever heard a dual mic phone was when one of my coworkers made a call from the inside of our data center. Typically, he'd have to shout into the phone, because the data center was so noisy, and worst of all, the noise was completely random and broadband. But with dual mics, poof, background noise is gone. It was almost like he was speaking in a quiet room. Amazon Alexa takes this quite a bit further, and uses something called "beamforming." What beamforming allows you to do is to determine WHERE the person is in the room, based on the arrival times of the sound. It's sort of the inverse of a dual mic setup; in a dual mic setup we can 'clean up' the signal because we know where the person speaking is. In a beamforming arrangement, we can use the arrival times to FIGURE OUT where the person is in the room. If some security company was clever, they could probably use a beamforming microphone array to train a camera on people in the room. And keep in mind, Alexa beamforming is two dimensional, but you could go crazy and do a 3D beamforming array if you wanted to! (Alex only knows where you are on a horizontal plane.) |