How to measure/calculate STI (Speech Transmission Index) from audio files in audacity?

Im trying to measure the STI of audio files but i cant find a way how to without paying for softwares. Is there any way to do it or any plugins i can put in Audacity?

The nearest native Audacity tool is “contrast” …
https://manual.audacityteam.org/man/contrast.html

Is there a plugin for it? Like for exactly measuring STI, if so could you send it? Thanks.