Sound-alike is not actionable, and anyone who claims it infringes should be dragged through the courts.

Not your voice, not your IP, not your right.

except to the extent that your voice may be part of your image, which is actionable: https://en.wikipedia.org/wiki/Midler_v._Ford_Motor_Co.

So, what do we do with actual people who have a very similar voice to some "more famous" person? It's quite silly when voices are far away from being unique to a person.

Could two researchers with different voices and manners of speech agree to provide longer samples of their voices? Then they would convert each sample to imitate the other's voice. It would be easy to contrast and compare, without any controversy.

So it's illegal for standup comics to do impressions? Or maybe there is some nuance here?

Thanks modeless, I appreciate the comment -- yes, I agree, there is a substantive difference between "us[ing] people's voices" and "[doing an] impression [of someone's voice]". It's good you pointed this out, law can be hard for swes, it can tickle the "unambiguous rule" part of the brain we employ every day.