What you really need is decent audio editing software. 'Goldwave' will open any avi file (obviously only the audio stream) & is a very powerful audio editor with numerous capabilities & filters. You can save the file in any format & bitrate you like although it can't produce variable or average bitrate mp3 files, only constant. Virtually everything I produce needs attention to the audio stream, even straight DVD rips. Filtering, editing, volume adjustments, retiming, resyncing, adding effects etc. are all quite easy & it's good fun too!
Goldwave is not free but I have a slightly out-of-date (but very stable) version complete with serial numbers (not cracks or keygens!) if any one is interested.
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