Re: What Frequency is used?
Indeed, by virtue of the technology, there can be no "ultrasonic" frequencies produced. However there are sonic frequencies that a lot of people can't hear.
A department that I supported QCing TV found that 2 out of the 12 staff (and yes, they were the youngest) complained about some high frequency whistle. It turned out to be 18KHz produced from the new LED studio lighting they were using.
The moral of the story is that they can embed HF sound in the ads, but they'll piss off some of their audience.