https://www.science.org/content/blog-post/things-i-won-t-wor...

Do you need to calibrate it to be able to repeat it, and does that calibration change if you are at a different altitude and in different conditions, such as humidity?

Does merely changing altitude (or ambient pressure) change voice enough to be considered different by a recognition or synthesizing system?

In reality, some phlegm aside, their voice is still the same in any way that matters.

If you knew people who didn't smoke and started (not uncommon in the 80s and 90s, quite a few people I know started smoking in university, or after the stress of a first job, some even later), and also the inverse, you can trivially hear it for yourself.

I guess you don't listen to Sinatra.

Although it does seem to affect some people more than others for sure, I guess it depends how and what you're smoking.