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Ilari Sivil

Ultrasound, IoT and wireless

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https://www.wired.com/story/ultrasonic-signals-wild-west-of-wireless-tech/

I've been thinking about ultrasound a lot lately. Thanks to information on the forum, I've found out that some companders on analog wireless devices may choke out the signal you actually want when dealing with ultrasound due to HF boosts in the system. The noise from an induction stove or an ultrasound motion detector are known examples. Apparently ultrasound is becoming more commonly used in IoT-devices for wake-up signals and inter-device communication in household stuff, so I'm quite curious about the future as well as the present state of things.

How many ultrasound related problems actually come up these days? What types of common sources are there, and how could they be dealt with?

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I don’t if I‘ve had a problem Ultrasound yet, but I did infrasound. This would engage the limiter on my recorder and got cured by by engaging the hpf on the mic. 

Ultrasound could behave similarly 

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8 hours ago, Constantin said:

I don’t if I‘ve had a problem Ultrasound yet, but I did infrasound. This would engage the limiter on my recorder and got cured by by engaging the hpf on the mic. 

Ultrasound could behave similarly 


I've had infrasound from handling noise compromise the dynamics of a recording. Probably everyone has. Engaging the HPF helps, as you mentioned. I'm not sure if using an LPF to get rid of ultrasound would be a good idea, though, since it might bite into the hearable top end around 16-20kHz if if the level of the unwanted signal is high enough, unless the filter slope is steeper. Doesn't having a steeper filter slope increase the risk of self-oscillation, though? That's my experience with synthesizers at least, and on cheaper recorders I've seen some pretty obvious lines on the spectrogram at the Nyquist-frequency from the steep antialiasing filter. With modern tech, an automatically setting notch could be possible, perhaps? It would probably be a lot simpler to just skip the compander and have digital transmission.

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