Alexa is always listening but not continually recording. It doesn’t send anything to cloud servers until it hears you say the wake word (Alexa, Echo, or Computer). But listening for wake words is harder than you might think.
Echo hardware isn’t all that intelligent. Without the internet, any request or question you ask will fail. This is because your commands are sent off to the cloud for interpretation and decisions. Amazon doesn’t want every conversation you have in front of a smart speaker to be recorded, but rather, just the commands you give the smart speaker. For this reason, the company employs a wake word to get the smart speaker’s attention. To accomplish this, Amazon uses a combination of fine-tuned microphones, a short memory buffer, and neural net training.
Fine-Tuned Microphones Pinpoint Your Voice
Voice assistant speakers, like Echo and Echo Dot, typically have multiple built-in microphones. The Echo Dot, for instance, has seven. That array gives the devices several abilities, from hearing commands spoken far away, to separating background noise from voices.
The latter is especially helpful for wake word detection. Using its multiple microphones, the Echo can pinpoint your location relative to where it’s sitting and listen in that direction while ignoring the rest of the room.
You see this in action whenever you use the wake word. Stand to the side of an Echo or Echo Dot and say the wake word. Notice the ring lights up in dark blue, and then a lighter blue as it circles and “points” toward you. Now, move several steps to the side and say the wake word once again. Notice the light-blue lights follow you.
Knowing where you are, helps the device focus on you better and tune out noises coming from elsewhere.
Short Memory Keeps the Speaker from Holding Too Much
Echo devices have plenty of storage, but they don’t use much of it. According to Rohit Prasad, the Vice President at Amazon and Head Scientist of Alexa Artificial Intelligence, an Echo can only physically store a few seconds of audio.
By reducing its capability, Amazon not only gives you more privacy (it’s one less place your voice is stored) but also prevents Echo from listening to entire conversations, limiting its focus to finding the wake word.
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Source : How Alexa Listens for Wake Words
