DC offset is normally caused by problems in the analog to digital conversion, resulting in a waveform that isn't centered on the base line — it's offset either higher or lower than the center line. This prevents the audio from being properly normalized to match other songs or audio material. BIAS Peak lets you remove the offset by choosing the "Remove DC Offset" function found in the DSP menu. Typically you'll be processing the entire audio file, so you'd do a Select All from the Edit menu. Choose "Remove DC Offset" from the DSP menu. Peak will automatically scan the entire audio file and remove any offset, after which the selection may be normalized.