Its most likely not ultrasound, but just on the high end of what's supported by these codecs. mp3 and other codecs are biased towards human hearing ranges but s

Its most likely not ultrasound, but just on the high end of what's supported by these codecs. mp3 and other codecs are biased towards human hearing ranges but support up to 30000hz I believe. Most people can't hear above 15000hz. Load up any 'dog whistle' app if you want to see this in action. I imagine these apps use somewhere about 15k where some of us can hear it but really won't notice it too much during the 'empty' spaces between music, commercials, etc. The middle aged and over execs and managers who approve of these schemes certainly can't hear it.