I'm so confused the difference between /ɪ/ and /ə/ on an unstressed syllable when I have to transcribe them phonemically such as: philosophy, visit, supermarket,...
I don't have that issue when /ɪ/ is on stressed syllable, such as: irritable, image,... When I look up some word on Cambridge and Oxford, I see a big confusing difference too.
While "di" is transcribes as /ə/ on Oxford, it is transcribed as /ɪ/ on Cambridge.
The actual quality of short unstressed vowel varies from speaker to speaker and from instance to instance. When speaking faster, some speakers will tend to reduce unstressed vowels to schwa.
There is also variation on how to represent this kind of variation in a dictionary. The range of vowel sounds that the human mouth can create is almost infinite, and so practically, the people who write dictionaries must make decisions "This vowel is sometimes slightly raised, but it is often not raised very much... should we write it as /ɪ/ or /ə/?"
IPA renditions are suggestions; they can't replace listening to the words as actually spoken by a variety of speakers. So click those links to the recordings of the word.
