[ITB]

More interesting is when we used to run Alexa commercials and it would cause a denial of service attack on ourselves with all the devices being triggered, particularly during the superbowl. In that case, we added some imperceptible noise to the audio stream so that Alexa wouldn’t trigger.

[shagie]

The other approach is to remove certain noise.

If there is nothing in the frequency range from 3kHz to 6kHz Alexa won't wake when a wake word is spoken. https://youtu.be/iNxvsxU2rJE doesn't wake up anything.

https://www.theverge.com/2018/2/2/16965484/amazon-alexa-supe...

> Apparently, the Alexa commercials are intentionally muted in the 3,000Hz to 6,000Hz range of the audio spectrum, which apparently tips off the system that the “Alexa” phrase being spoken isn’t in fact a real command and should be ignored.

Compare that with selecting 'Alexa, what time is it' (I'm on a Mac) and doing "speak text". Same speaker (for me with the previous video).

I had one device set with a wake word of "Amazon" but that got really annoying when watching AWS training videos. I believe Ziggy is the best wake word for that reason.

[hughesjj]

I'm guessing this is because plenty of speakers aren't designed to output sound outside of typical hearing range (because, I mean why bother for a TV etc)

[shagie]

If you watch https://www.youtube.com/watch?v=lugeruSbnAE you will get Alexa waking up.

Meanwhile https://youtu.be/iNxvsxU2rJE and https://youtu.be/8bACuhV5RPM and don't.

Play them on a TV or tiny computer speaker.

You can hear 3 kHz quite well. https://www.youtube.com/watch?v=AacTD0HtadE

And we can hear up to 20 kHz when young (that's 3 octaves higher than 3 kHz). https://www.ncbi.nlm.nih.gov/books/NBK10924/

And while this is audio people talking about sound... https://repforums.prosoundweb.com/index.php?topic=22875.0

> 3k is commonly the most sensitive frequency for human ears - we use it for testing wow and flutter on tape machines; you can hear pitch variation there easiest. 3k is a ballpark, but a good one - I think it works anywhere in that region 2-4k, but usually 3k is THE ONE.

> When I have a harsh fuzz guitar or trashy cymbal, I often try to just tuck down the 3k region, and suddenly it no longer covers everything. It still sounds thick and harsh, but nothing kills your ears.

> ...

> Cutting at 3k can help hide out of tune instruments and bad pitch on vocals as well.

---

Late edit. Extracting the audio of the "Alexa looses her voice" and sending it into https://academo.org/demos/spectrum-analyzer/ - watch at the range around 5.1 kHz (about the center of the 3 kHz to 6 kHz octave). It starts out with: https://i.imgur.com/iEe7s6P.png

That spike is the actress saying "Alexa" and you can see the unnatural gap in that range. Also, there is sound in that mp3 all the way out to 14 kHz.

[imranq]

Wow that's cool - that's like those adversarial attacks they do on self-driving cars to make it think a stop sign is a gorilla

How do you know what noise to add?

[kqr]

...or did you specifically use some sort of fingerprinting noise that Alexa was programmed to ignore?

[JoBrad]

How do you differentiate a noise source that contains a signal, vs another sound playing at the same time as your signal?