Does k have to be voiced before vowels in Russian?

Turbid and clear are collectively called "assimilation", which refers to the changes that occur when voiced consonants are adjacent. Assimilation is generally the other way around. Simply put, two consonants are together, and the latter affects the former. If the last one is voiced and the first one is voiced, then the first voiced consonant should be pronounced as its corresponding voiced consonant, such as вокза. Of course, there are some cases, such as the consonants are not clear before в, and they are not clear before м, н and р. Therefore, к is not because it is voiced in front of vowels, and it has nothing to do with vowels, but mainly depends on the consonants at the back.

The light tone symbol (ь) indicates that the consonant before it is a soft consonant, such as мать (mother), and you can't pronounce мат (become another word, meaning swearing). ьь also has a sound separation function, that is, the consonant in front and the vowel in the back should be read separately, such as статья.