From inSync reader Christopher G. comes the question, “Could you please explain DC Offset as it relates to DAT machines and digital editing? I see it as a tool in ProTools and don’t really know what it does or why it would be good/bad.”
DC offset in a digital audio program is a command that is used to remove the DC component from audio signals recorded in the system. I can’t think of any cases where it is desirable to have DC present in recorded audio signals so most programs have a utility for its removal. There usually aren’t any parameters to set or anything, you just tell it to remove the DC and it does. It’s pretty easy to see or hear DC when present in a digital audio workstation: It will appear on screen as your audio signal waveform residing mostly above or below the zero line as opposed to the normal 50% split. You can hear it as a pop or click whenever you start or stop playback or audition an edit. When you see or hear this problem simply apply the DC offset command to the audio to remove it.
Sometimes an A/D converter can get out of adjustment and record DC all the time. An easy way to check this in a system like Pro Tools is to simply record a few seconds of silence with nothing plugged in to the audio input. When you view the waveform (which hopefully will show up as a straight line) it should appear right on top of the zero line. If you get a straight line consistently residing above or below this line you may need to have your converter box checked.