[robotresearcher]

Have you ever seen a real world example of 'ultrasound' used to mean anything other than higher-than-audible frequencies?

Wikipedia's definition has it explicitly higher. https://en.wikipedia.org/wiki/Ultrasound

That page says:

> Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz".

'Ultraviolet' means only higher-than-violet.

We have another word 'infrasound' for lower-than-audible frequencies.

I'm a native English speaker technically interested in sound for 40 years and I have never heard the 'subtlety' usage.

[ddingus]

This is an entirely fair comment. And it's typical of my experience as well, and I have a fair amount related to audio, though not as extensive as yours.

My mind works differently when it comes to language and the scope of possible meanings is something I always consider relevant.

What concerned me here was someone taking the colloquial definition of "ultrasound" literally, and making assumptions that are not valid in this context at all.

What the word actually conveys is both a matter of subtlety and frequency.

Turns out, having read the entire discussion, both are relevant in terms of threat assessment, and thinking about what is said more deeply can have a positive impact on a discussion of this nature.

All of which is why I chose to point out what "ultrasound" actually does mean linguistically.

Edit: In my experience, such uses can and do happen. I personally allow for it and use context to parse. Where there is ambiguity, I generally won't dismiss it out of hand.

Subsonic comes to mind here. As does the question why the word did not appear regarding these watermarks.

The answer may just be someone with far less domain expertise attempting to communicate.