the verb "believe" in some dictionaries shows as [bɪˈliv] and in some dictionaries as [bəˈliv] with a schwa sound. Does it matter which one I use considering that the change is in an unstressed syllable anyway? For example I pronounce the phrase "I believe you" in two different ways. First I pronounce: [bɪˈliv] then [bəˈliv]: https://dl.dropboxusercontent.com/u/1924024/Ibelieveyou.wav I think the stress is on [ˈliv] and that is the most important in the phrase I believe you. Any suggestion appreciated.
Both /ɪ/ and /ə/ are found in standard varieties of English in the prefix be- it does not matter which you use; they're both perfectly acceptable. The most important point is that you shouldn't stress this prefix.
In the phrase /aɪ bɪ'liːv ju/ we would normally expect the syllables /aɪ bɪ/ to be said at a low level pitch (where they form the pre-head of the intonational phrase). The nucleus, /'li:v/ will be prominent and said at a high pitch. The syllables /li:v ju/ will usually have the pitch contour of a high fall nuclear tone. So /li:v/ at a high pitch will be immediately followed by a very low pitch unstressed /ju/.
The reason believe will carry the stress here is that pronouns are usually unstressed in English. The nucleus will normally fall on the last word representing new information in the sentence. In this case this is the word believe.
The difference is very subtle. Fluent English speakers in America say it both ways. Either is acceptable. (I don't know if one or the other is preferred in other English-speaking countries.)
It's possible that this is a regional thing. If so I haven't noticed.