This command normalizes audio to a specified maximum level. It can normalize the channels together or individually, and can optionally correct DC offset (bias). If a selection exists, only the selection is normalized, otherwise the entire document is normalized. The command displays the Normalize dialog, which provides the following options:

Remove DC offsetCheck this option to correct DC offset. This is done (for each channel) by summing the samples, and then subtracting the resulting sum from each sample.
Normalize toCheck this option to normalize the audio. The audio is normalized to the specified peak level, in decibels, which can't exceed zero. Note that it's possible to correct DC offset without normalizing, and vice versa.
Normalize channels independentlyIf this option is checked, each channel is independently scaled to reach the peak level, potentially changing its volume relative to other channels. Otherwise only the loudest channel reaches the peak level, and the others are scaled proportionally, in order to preserve the channels' volume relationships.