Re:Hackers send silent commands to speech recognition system...
by femto on Friday September 08, 2017 @08:54AM
(#15199773)
Harmonics are multiples of the fundamental, so in this case they will also be ultrasonic.
Equation 2 in the paper and the subsequent paragraph shows what is going on. They use an ultrasonic carrier with modulation. The non-linearity causes the carrier to mix with the sidebands, the third-order intermodulation product being a copy of the modulation centred on 0Hz (ie. a baseband signal).
Edit: Figure 12 talks about harmonics, in the context of harmonics of the third order intermodulation product. What they are really refering to are the higher order: 5th, 7th, and so on intermodulation products, which in this case will be multiples of the third order product's frequency.
Equation 2 in the paper and the subsequent paragraph shows what is going on. They use an ultrasonic carrier with modulation. The non-linearity causes the carrier to mix with the sidebands, the third-order intermodulation product being a copy of the modulation centred on 0Hz (ie. a baseband signal).
Edit: Figure 12 talks about harmonics, in the context of harmonics of the third order intermodulation product. What they are really refering to are the higher order: 5th, 7th, and so on intermodulation products, which in this case will be multiples of the third order product's frequency.