The description that follows is of a modern Standard Yiddish that was devised during the early 20th century and is frequently encountered in pedagogical contexts.
Stressed vowels in the Yiddish dialects may be understood by considering their common origins in the Proto-Yiddish sound system.
Yiddish linguistic scholarship uses a system developed by Max Weinreich in 1960 to indicate the descendent diaphonemes of the Proto-Yiddish stressed vowels.
Lastly, the Standard German /aʊ/ corresponds to both the MHG diphthong ou and the long vowel û, but in Yiddish, they have not merged.
Yiddish deaffricates the Middle High German voiceless labiodental affricate /pf/ to /f/ initially (as in פֿונט funt, but this pronunciation is also quasi-standard throughout northern and central Germany); /pf/ surfaces as an unshifted /p/ medially or finally (as in עפּל /ɛpl/ and קאָפּ /kɔp/).