Learning how to pronounce the Vedic Mantras in the Sanskrit language is a fascinating thing–however, there are various intricacies that are involved in pronunciation when it comes to Sanskrit, and more so when it comes to Mantras.
Even Indians, though they easily pick the sounds of the Sanskrit alphabet, usually do not know these deep secrets and significance of various modalities.
It is always suggested that if you could find a learned person, it would be great to learn the Mantras, the chanting, the intonation etc. directly. However, if you are practicing on your own, here is a Shanti Mantra with Roman transliteration and also the Svara marks in both English and Sanskrit so that you could know how to pronounce and where to change the stress etc.
Feel free to leave your suggestion or feedback through the comment section.