As brought up by this question
As the topic affects interpersonal skills (i.e .being too annoying for others to properly hear you) it could be considered ontopic, however, it also isn't a specific instance of an interpersonal skill, nor is it an exact situation involving interpersonal skills. So is it, and other questions like it, on topic for this site?
Yes. I don't see a problem with this question.
"Skills" doesn't just mean coming up with an applied solution for a specific instance or recurring problem with other people. Skills also includes smoothing out our own personal quirks and behaviors to facilitate better interaction and communication with others.
If the question was how to greet someone with a proper handshake, I think we would all agree that is on topic. So it should be small step from there to see how tempering your voice to be more pleasing in social situations should be on topic too (and questions like it).
