If you are getting an "ineligible" message when trying to upload some of your music tracks to iTunes Match, chances are, one of two things are happening. First, your track may be over 200 MB. If so, that's a long audio track...all you can do is edit and trim to downsize and try to re-upload. The second problem is more common, and it's the focus of this post: it's likely your music track was encoded at a low bitrate that doesn't meet iTunes Match's 96 kbps requirement. Let's see how to fix this.
Re-encoding low bit rate music to high quality AAC
Step 1: In iTunes 11+, go to iTunes - Preferences - General - Import Settings, and make any changes you need to from the drop downs to match below then click OK and OK to get out of Import Settings and Preferences:
Store, Update iTunes Match