I didn't hear it before
I do hear it before
pro:sub mod v pro:per adv
i didn't hear it before.
aɪ WORD_BOUNDARY d ɪ d n t WORD_BOUNDARY h ɪ ɹ WORD_BOUNDARY ɪ t WORD_BOUNDARY b ɪ f ɔ ɹ WORD_BOUNDARY
i WORD_BOUNDARY d i d n ' t WORD_BOUNDARY h e a r WORD_BOUNDARY i t WORD_BOUNDARY b e f o r e . WORD_BOUNDARY