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View Full Version : How to fix DC offset?


xcv111
2007-10-22, 07:13 PM
I've been trying to fix DC offset right - by right I mean 0% of DC offset - without no success. Choosing a long sample, Cool Pro 2.0 shows by analysing that DC offset is 0%, but when I pick up a shorter sample - let's say 5 sec. - the result is something more like this: left channel -.014 and right channel -.01. Or worse.

The "trouble case" was recorded with Yamaha CDR-HD1500 digital recorder. And there shouldn't be - in this case - an analog lineage involved, since the audio was digitally recorded from digibox optical cable used. A sound card problem - yes? I ripped the "trouble case" with EAC (secure). Then I opened the files in Cool Pro 2.0 and this is the procedure I tried to get DC offset corrected: Amplify > Centre Wave > DC Bias Adjust > Absolute. I've also tried out Cool Pro 2.0's DC Bias Adjust > Differential -procedure with no better results.

So? How do I get DC offset to 0%?

All the best,
xcv111

Ps. Yes. I did read through FAQ and the Technobabble Archive, but I didn't get an answer from these forums for my problem.

paddington
2007-10-22, 09:37 PM
Many sound cards record with a slight DC offset, which means that direct current is introduced into the signal by the card, causing the center of the waveform to be off from the zero point in the waveform display. This is seen as the waveform being “shifted” above or below the center line in the Wave Display, and can cause a click or pop to be played at the beginning and the end of the file.

To compensate for DC Offset, you can choose the DC Bias Adjust setting in Effects > Amplitude > Amplify.

xcv111
2007-10-23, 12:07 AM
Amplify > Centre Wave > DC Bias Adjust > Absolute. I've also tried out Cool Pro 2.0's DC Bias Adjust > Differential -procedure with no better results.
Yup. Exactly. Like I mentioned, as you can see above, my procedure I tried out was quite much the same as yours.

paddington
2007-10-23, 12:23 AM
shows by analysing that DC offset is 0%, but when I pick up a shorter sample - let's say 5 sec. - the result is something more like this: left channel -.014 and right channel -.01. sorry, I missed a lot of that before... both of those are really low... I know you'd like to see 0% everywhere, but I really don't think you'll have an issue with .01%.

I'd expect that the whole wave is likely avg 0% is what it is telling you? I know you shouldn't get anything at all in theory, but those figures are quite low. I just opened CEP on this machine (a laptop with an avg card) and recorded 10 secs of nothing and analyzed the bias stats... .894% and 1.012%. Much worse than your .010%! Now this is just an avg sound card thing, so I;d expect it to be not-great - but just to give you an idea of how much better yours is than a stock card recording nothing...

xcv111
2007-10-23, 12:38 AM
So, I guess there's no really acceptable DC offset level? 0% is the optimal level. And that's that.

Or is it? Could acceptable level be the one can't hear? I guess not really...

xcv111
2007-10-23, 01:35 AM
Thank you mr. Blue Sky Road Sign aka JamesKg for putting some "common" sense into my head.

Your reply set the perspective/horizon where it ought to be and eased my mind quite a bit. Thou I'm even still looking for the solution for the 0% DC offset...

Thanks.

cicada
2007-10-24, 07:19 PM
I/m struggling with my own issues including dc offset. I just got a link to this site to help me sort out my questions. I thought I would share. Not sure if it will answer your question, but it seems pretty good to start http://www.harmony-central.com/articles/tips/eq_dc_offset/

Good luck!