Compound vowels are basically the combination of two simple vowels. There are total four compound vowels which are the combination of eight simple vowels. The compound vowels and the long vowel are pronounced for a same number of times. The difference between a simple vowel and a compound vowel is that compound vowel has relatively more strength when pronounced.

Compound vowel has three categories of strength:

Weak vowel: they are basically simple vowel. The time taken to pronounce them is same as those of simple vowels (i, i)

Medium vowel: adding an “a” sound in front of the weak vowel we get a medium vowel. (ai)

Strong vowel: by strengthening the “a” sound in the medium vowel we get the strong vowel. (*ai)

Medium vowels

“e” as in “lane” “ai”
“o” as in “go” “au”

Strong vowels

ai combination of a and i
au combination of a and u