My cell phone samples at 48000 samples/sec so the FFT app I installed can only detect frequencies up to 24 kHz.
If anyone has an audio frequency analyser that can go higher, would you please use it on a digital TV advertisement for Amazon Alexa and see if they are embedding any sort of ultrasonic signal to tell the device not to respond to the keyword?
When it first came out it responded to the word Alexa on TV all the time and now it almost never does. My guess is an ultrasonic signal is being used to suppress the keyword recognition. No-one has talked about this online or in the press that I can find, so I'd like some confirmation if this is true. (I can't see any other way they would be doing it that doesn't involve sending samples to Amazon which they should not be doing since the recognition light is not activating at all for these events)
So my question is whether an ultrasonic signal is present in Alexa TV ads and if so, what is it composed of?