DC offset 2

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faderbug

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could someone please explain to me exactly what a dc offset is and how it effects your sound?!
 
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Newbie ain't just my BBS status.

Inquiring minds want to know!
 
It is when the difference between the posotive and negative voltage of your audio signal is not averaging at zero. It can cause a barely or inaudible low frequency distortion in your audio. If an input is giving a consistent bad offset it can get much worse as you add tracks to a mix.

If it is bad enough to see, meaning the waveform is more below the line than above, it is probably bad enough to mess with your audio quality. It also makes it strange to apply plugins that are optimized to zero average audio.
I really don't know all the details but that's the basic idea as I understand it.
 
low frequency distortion? i'm not so sure about that.

DC offset moves the waveform from the centre (neutral, calibrated voltage) line. it basically just means that the voltage levels of one piece of gear are not agreeing with what the software is expecting to see. So like it you have a positive DC offset of +0.01 volts, it's going to mean that the digital representation on the vertical (amplitude) axis will be offset by that amount.

All it really does it reduce your headroom for gain, because it moves the peaks of the waveform closer to the edge (digital zero).
 
www.bu.edu/webcentral/learning/av2/optimize-dcoffset.html

That is what I had read a while back, I actually got it wrong. They say an "inaudible low frequency distortion".

That's Sonic Foundry though not a professor.

Any one have a link to a more scholarly explanation? I am very interested to read more now. I know that it is an imbalance between - and + but in digital audio I would imagine that can have different consequences in digital audio.

Is that wrong?
 
Hi,

I'm sure this subject has been discussed to the limit from time to time here. I would love to find a post where a sonusman type person wrote on the subject.

I just mastered an old live recording (studio) made with lots of outboard gear/hardware that potentially might add DC offset...right? I adusted for offset on all the tracks and the end result sounded pretty damned good.

Someone earlier or in another thread stated that it was on "mono" tracks. This baffled me at first since it seemed to me that the DC offset, if it was there at all would be on stereo tracks as well but I think it must have been the "fix" he was refering to....so I split all my stereo files and adjusted for offset bias individually.

I need a "heavy hitter" to weigh in on this one as I'm sure they have before. Where is that sonusman when you need him!

Rusty K
 
Update!

Hi,

Well I've redone work since I found that all the dc offset generated in the studio tracks I was working on was negligible.

My own gear is creating a dc offset but only on some tracks. The only things different in the chain are the instruments mic/guitar/bass. I didn't realize they would be considered part of the "hardware chain".

Also if I have dc offset in stereo tracks or if the percent of offset is different for the respective channels whouldn't I apply the "fix" to the channels separately since they both have center points. It doesn't seem logical to apply a dc bias adjust with differing values, L/R to the whole file.

Thanks,
Rusty K
 
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