Church Slavonic is a literary and liturgical language, which means that historically it has been used more for reading and ceremony than casual everyday speaking. That's perfectly fine, and this makes Slavonic analogous to Latin and Greek as classical languages of high culture in Europe and America. But like Latin and Greek, there are differences and disagreements over the "correct" pronunciation of Slavonic texts. As it turns out, there are a number of dialects or literary recensions of Church Slavonic. Differences in pronunciation that you notice in this podcast are likely to be between the Russian pronunciation (including "reduction" of unstressed vowels) and Bulgarian pronunciation in which vowels are not reduced.