correct DC offset or uneven audio

I corrected the DC offset so the base line is centered, but I can't really 
hear the difference. Because the original baseline moved toward the 
bottom, the bottom part was much shorter than the part above the baseline.

With that, you can't normalize it further. The volume is low since the 
upper side is over the edge. How can the audio like this be further 
enhanced?

I also found some recorded audio without DC offset problem but has a 
little bit difference in length below and above the baseline. Is it 
normal? What does it tell about the recording device?

Thanks for the help,