There are a couple ways you can go about this process. If your songs are too quiet you can adjust their volume in iTunes.
This is easily done with selecting the songs you want to boost (Control+Click, Shift+Click or ).

Control+Click or right click and select Get Info. Select the checkbox and slide the volume bar up to 100%. Select OK and your songs will be updated. Be sure to sync your iPod with the new songs.
If your iPod is too quiet, there is a program out there called goPod that will increase it’s volume.

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