Urgent Issue - DC Offset?

Question

I could REALLY use some help with this one. I've just started working on my first real feature film, and unfortunately the sound in the OMF given to me is a wreck.

My biggest issue is some audio files are EXTREMELY quiet and when I try to gain stage them (Pro Tools 10 using the clip gain feature) the audio wave only expands downward, the top seems to 'flat line' (like clipping) right at the zero crossing line and in some cases I can clearly see the zero crossing line above the wave form.

Is this DC offset? I've NEVER had to deal with DC offset before....

Answer 1

Good discussion about DC Offset here on the DUC:

http://duc.avid.com/showthread.php?t=193739

There could be something wrong with the preamp or mic wiring.

Try using the AudioSuite plug-in to remove the offset. If it doesn't do the trick, maybe it's not strictly a DC offset.

Answer 2

It may be extreme DC offset, or a rectified waveform. Hard to tell unless you link to a picture.

Depending upon what the situation is there may be options, but first we need to see the waveform to find out what's really going in in my opinion.

Answer 3

This could also be a faulty cable, where the positive (hot) part of a balanced signal did not arrive at the recorder.

Typically, DC offset means a signal is centered around a value other than 0, so when looking at the waveform, you see that even when nothing is playing, the waveform is consistently higher than 0 in case of a positive offset, or lower in case of a negative offset.

There are DC-offset filters that don't harm the sound otherwise, essentially it's a high-pass filter set to 0 Hz - DC offset is a 0 Hz signal.