Computing of speech signals modulation entropy
Ok, I've found what i was looking for.

This paper describes how to measure entropy in signals: 

Entropy Based Voice Activity Detection in Very Noisy Conditions, by Philippe Renevey and Andrzej Drygajlo. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.123.6098&amp;rep=rep1&amp;type=pdf

And this question covers the part of coding side of question:
https://stackoverflow.com/questions/18962990/calculate-entropy-of-a-file