The two pronunciations in question are (in IPA):
- /ˑkɑmp(ə)rəbəl/ (KOM-pruh-buhl)/(KOM-puh-ruh-buhl)
- /kəmˑp(æ/ɛ)rəbəl/ (kuhm-PARE-uh-buhl) [approximately]
Pronunciations for this word are given in dictionaries in four ways, as far as I can tell:
- (a) both are given in the order #1, #2, with no comment
Webster’s New World
- (b) both are given in the order #1, #2, but the second is noted as “less common” with a notation like “also”, or “or, sometimes”,
Merriam-Webster, Random House,
- (c) both are given in the order #1, #2, but the second is noted as U.S.-only
Cambridge Advanced Learner’s, Wiktionary
- (d) only #1 is given
American Heritage, Collins, Macmillan, New Oxford American
No dictionary I looked in lists pronunciation #2 first. Nor does any support different meanings for different pronunciations. Generally speaking, #1 is the traditional and unimpeachably correct pronunciation. #2 is commonly used, but if you use it, you should not be surprised if you are criticized or corrected.
Addendum: the user-provided pronunciation site Forvo has seven pronunciations for comparable. The two pronunciations which are pronounced like #2 are rated –3. The rest, which are pronounced like #1, are rated 0, 1, or 2.