Increasing the bit rate of the mp3 audio files always increases it quality in listening and make it more clear, here is this small free portable program called MP3 Quality Modifier which lets you improve the quality of the mp3 files on your computer by changing the bit rates and sampling frequency of these files.
You can also play the songs via program interface, the user interface of the program is quite simple you just need to add the song select the bit rate mode and sampling frequency and output location of the converted mp3 files and click the label in the program toolbar on the right top corner saying start process
This mp3 modifier program can really save some disc space, and the best part of this tool is that it retain all the ID3 tags (title, album pictures etc.). It will also show you the size of the original and the output file after changing the bit rates and sampling frequency.
Download MP3 Quality Modifier