Alexa will no longer be accidentally triggered by TV ads, including the Super Bowl LII commercial, and it's all thanks to what Amazon describes as "acoustic fingerprinting," among other things.

That means any mention of Alexa's name on the small screen or, say, a YouTube video won't wake up users' Echo devices out of the blue and cause them to follow unwanted commands.

Alexa's Acoustic Fingerprinting

In Amazon's words, acoustic fingerprinting allows Alexa to differentiate users' utterances of its name from those that come from ads.

"The trick is to suppress the unintentional waking of a device while not incorrectly rejecting the millions of people engaging with Alexa every day," Shiv Vitaladevuni, one of the Alexa Machine Learning team's senior managers, says.

This is part of the patent that Amazon filed in September 2014 titled "Audible command filtering."

Now the retailer didn't specify how this works exactly, but as Bloomberg notes, there are two techniques at play here. The first of which is that an ad's snippet will be sent to the Echo before it even airs so that the smart speaker can compare live commands against its acoustic fingerprint and make a distinction between the two. The other measure is that an ad can let Alexa know to ignore its wake word via an inaudible acoustic signal.

Bloomberg also points out that a Reddit user may have gotten to the bottom of things when it comes to the second method.

The Trick Behind The Trick

The Redditor in question is named aspyhackr, and they explained the possible inner workings of Alexa in a post that's at least a year old.

"I did a little research tonight and found that the Echo, while it's processing the wake word, searches the Audio Spectrum and if is significantly quieter in the area of 4000hz to 5000hz, she will not wake for the word ... [W]hen I analyzed the spectrum of them saying her name, the spectrums were significantly quieter in the range of 3000hz to 6000hz. In some of those recordings, those frequencies appeared to be non-existent. In others it appeared like the boosted the surrounding frequencies to make the Echo see a gap in the spectrum."

Put differently, if Alexa is picking up some gaps or detecting any similar anomalies in the spectrum, then it'll just ignore what it's hearing, such as its wake word and other commands.

Of course, this works out well if everything is planned out, but in terms of unanticipated mentions, there could be problems on the horizon. In other words, Amazon needs to have edited the audio of a commercial for this technique to work, and that means wake commands that turn up unexpectedly will trigger Alexa in this context.

For instance, a TV report back in January 2017 in San Diego, California, led to mass orders of dollhouses when the newscaster said, "I love the little girl, saying 'Alexa ordered me a dollhouse.'"

The Bottom Line

Echo devices won't be waking up all of a sudden, even if the TV calls Alexa. However, that won't be the case every time.

Needless to say, this measure is just what Amazon needs for the Super Bowl LII ad, as the 90-second clip does mention "Alexa" 10 times during the minute-and-a-half period, which featured Amazon CEO Jeff Bezos.