Long Vowels

ā is a low back open vowel, very close to [-aa-] in ‘aardvark’ and [-a-] in ‘father.’
u is invariably a high back round vowel, very close to [-oo-]. Compare and contrast the English word ‘poor’ and Persian پور pur ‘son (of)’. Unlike English, there is no off-glide.
i is invariably a high front vowel /ī/, very close to [-ee-] in ‘cheese’ and [-ea-] in “please”; it is never a central /i/ (as in “sit”).

Listen to the long vowels in the following set:

starling ā as in sār سار
feast u as in sur سور
garlic i as in sir سیر

Note that in Classical Persian, some words with a terminal long vowel [ā] and [ū] have a variation with a ی following that vowel:

پا

پای
pāy
‘foot, leg’

خدا
xodā
خدای
xodāy
‘god, God’

جو

جوی
jūy
‘stream’

مو

موی
mūy
‘hair’

In addition, some interjections, such as آی āy ‘an expression of pain; also ‘ahoy!’ and وای vāy ‘an expression of surprise and astonishment’ have the [-āy] ending. Therefore, in Persian—at least historically—the diphthongs āy and ūy also exist (see Diphthongs).