from the article:
Does the company's technology work on the dog whistle principle, using sound waves that are below the threshold of human hearing? No. If it did, you couldn't send the signals over standard audio speakers.
Instead, the technology revolves around what's called psycho-acoustic masking. Humans tend to filter out what they don't want to hear, especially the pop, fizz and hum of white noise. Intrasonics essentially takes and digitizes recorded messages, and then masks them as nuisance noises. The signals are spread over the audible spectrum and then disguised into the soundtrack. During a crescendo, the signals can be louder than quiet moments and still remain undetectable.
A processor, equipped with specialized software, in the receiving unit then reassembles the message and delivers it accordingly. Tests reveal that people don't hear the signals.
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from the article: Does the company's technology work on the dog whistle principle, using sound waves that are below the threshold of human hearing? No. If it did, you couldn't send the signals over standard audio speakers. Instead, the technology revolves around what's called psycho-acoustic masking. Humans tend to filter out what they don't want to hear, especially the pop, fizz and hum of white noise. Intrasonics essentially takes and digitizes recorded messages, and then masks them as nuisance noises. The signals are spread over the audible spectrum and then disguised into the soundtrack. During a crescendo, the signals can be louder than quiet moments and still remain undetectable. A processor, equipped with specialized software, in the receiving unit then reassembles the message and delivers it accordingly. Tests reveal that people don't hear the signals.