Correcting mp3 audio (crackling, static, hissing)

[RoninV]

Until recently, I had only used WavePad for the occasional audio conversion, but now using more often to correct audio imperfections and enhance audio outputs. My situation...

 

In preparing a DVD Slideshow (Photo Story 3, Movie DVD Maker), several .MP3 audio files can be heard at various moments. After Photo Story 3 creates the slideshow (.WP3 converts to .WMV), Movie DVD Maker makes it DVD playable. Several of the tracks have crackling/hissing. I figured 'high-pass filter' or one of the 'noise reduction' features was my best option, since I would be simply using WavePad's batch feature instead of analyzing each .MP3 one at a time. I was not sure whether high-pass would work, since it tends to focus on the low frequencies (I could be wrong), so I went with 'auto spectral subtraction' at its default settings. After adding the edited .MP3 back to the slideshow, I created the .WAV. When making the .WMV playable on a DVD player, the audio settings were 448kbps and stereo channels. The resulting .MP3s have no crackling/static, but a few tracks sound wobbly (singer sounds like he/she is under water). Based on my situation, should I have gone another way in trying to get rid of the crackling/static?