Consonant voicing and devoicing - Upodobnienia pod względem dźwięczności

Cześć!

I was wondering if someone could explain this concept to me, as I don't fully understand what my textbook is telling me. I know that in combination with other letters, written głoski i.e. rz will be softened to sz when next to another unvoiced consonant, like k, or p.. but there's a section in the book that says:

"Utrata dźwięczności to ubezdźwięczienie, nabycie dźwięczności to udźwięcznienie Warto jeszcze zapamiętać, że wszystkie upodobnienia wewnątrzwyrazowe pod względem dźwięczności są martwe."

Dzięki!
(sorry if this is already a thread, but i couldn't see it anywhere thus far :))

It probably means that some letters within some Polish words, like: studniówka or krzyżówka or przetrwać will always lose their 'udźwięcznienie' (in these three words the letter 'w' sounds like 'f' when you say these words, ie. they lost their 'dźwięczność').

In phonology, devoicing or desonorization is a sound change where a voiced consonant becomes voiceless due to the influence of its phonological environment. Most commonly, the change is a result of sound assimilation with an adjacent sound of opposite voicing, but it can also occur word-finally.

Consonant voicing and devoicing
en.wikipedia.org/wiki/Consonant_voicing_and_devoicing

Utrata dźwięczności / ubezdźwięcznienie = devoicing / desonorization

upodobnienie martwe = diachronic or historical sound change

Assimilation (linguistics)
en.wikipedia.org/wiki/Assimilation_%28linguistics%29