MojoMove Voxcast #1 contains an excellent discussion (by Ticktockman and Robert) on DC Offset in your recordings: what it is and how to remove it.

You can see the effect of DC Offset when you are recording audio, and the waveform is not correctly centered around the mid point line in an Audacity  track (i.e. the zero volt axis).  It usually manifests itself as a low rumbling sound in the recording.  This can become a big problem if you don't record with a high enough level, and then try to normalize the audio to make the speech louder - because the rumbling noise also gets louder and can drown out your speech.  

Although VoxForge prefers audio submissions without any noise reduction (in order to get speech from as many different "natural environments" as possible), we will gladly accept any transcribed speech recordings.

thanks, 

Ken

--- (Edited on 10/8/2007 3:36 pm [GMT-0400] by kmaclean) ---