Complex sentence: The most notable difference between Old and Middle Dutch is in a feature of speech known as vowel reduction; while round vowels in word-final syllables are rather frequent in Old Dutch, in Middle Dutch, such are leveled to a schwa.
Split into simpler sentences: The most notable difference between Old and Middle Dutch is in a feature of speech known as vowel reduction. Round vowels in word-final syllables are rather frequent in Old Dutch, in Middle Dutch, such are leveled to a schwa.