I are trying to amplify a recording made on a Creative mini-Zen portable recorder. When I look at the wave pattern, I can see that most of the sound is centered below the zero line. Only when the sound is loud does it "peak" above the zero line. 
It sounds okay, but if I amplify it, it clips the botton of the wave. I would like to just move everything up. I am using the free version of Wavepad. I could not find a command that adds "Bias" to shift the center of the recording. Does such a command exist in this or other versions?
Thank You