Translation:Shulchan Aruch/Orach Chaim/62
62: One who was not precise with reading the Shema or did not make an audible sound.
1 Even though it is a mitzvah to be precise with its letters, one who read it without being precise has fulfilled his obligation.
2 One may read it in any language, and one should be careful to avoid mistakes in that language and be precise with it just as if it was in the Holy Tongue.
3
One must be able to hear the words coming out of his mouth, and if one did not hear them, one has fulfilled the obligation as long as he brings them out with his lips.
4
If due to illness or another mitigating factor, one read the reading of Shema in one's heart, one has fulfilled his obligation.
Gloss: And one should do so even from the start if one is in a place that is not completely clean and one cannot clean it up due to unavoidable circumstances, one should think in his heart. And this is only if the place is not completely filthy because it is forbidden to ponder matters of Torah in a filthy place [Beit Yosef, Chapter 85].
5 The person leading prayer must make his voice heard with "Shema Yisrael" in order that the congregation will hear and will crown the name of Heaven together.