Mastering & DC offset

[SouthSIDE Glen]

Oh, is that how you know if it's offset or not??? I didn't know that.

Does that mean that if I don't get those pops, I'm OK??? Or it's not as simple as that???

Not necessarily that simple. Pops and clicks can have other causes. Also it's possible that you may have offset where the pop or click may not be noticed (if you're not paying attention, if the offset is not huge, if your loudspeaker is not the best, etc.)

Remember that offset is basicaly much like a DC bias voltage. If you apply a perfectly quiet track with DC bias voltage on it, this voltage will cause a loudspeaker to instantaneously move either in or out (depending upon the polarity of the bias) and will *hold it* at that non-rest position until the current is removed (in this case, when the audio clip is done.)

That instantaneous move is what causes the (usually, but not necessarily) audible transient at the start and/or stop of the clip. It may not necessaily be reaily audible for a number of practical reasons (monitor amp turned down, a loudspeaker that's slow to transients, etc. wax in your ears ,etc.) It usually is audible, but if it's not audible - sorry Brad, I gotta disagree on this one - that doesn't mean you don't still have a monkey on your audio back.

G.

 

[masteringhouse]

Just curious.

Everyone in this thread who has mentioned "seeing" DC Offset......Did you hear any difference when you removed it???

Other than clicks it will depend on if you can hear a signal below 20 Hz. Most cannot.

 

[masteringhouse]

One question I have had about this subject ever since I started using NLEs is, is there any source of information describing just how the "DC Offset" process in the various software titles does it's job? Not analog offset circuitry, for which there is a plethora of information. but digital software processing.

G. If you haven't seen it already this may give a bit of insight:

http://www.dsprelated.com/showmessage/22173/1.php

 

[SouthSIDE Glen]

Other than clicks it will depend on if you can hear a signal below 20 Hz. Most cannot.

Tom, thanks for the link, I'll check it out...as soon as the NFC Division game is over .

[EDIT] OK, I decided not to wait . It looks as though my idea of simple offset subtraction does not work, if I read that correctly. I guess I still have a bit of leanin' to do, as many of the other responses were of a level where I understood *what* they were saying, but just not *why*. Probably stuff way beyond the scope of this forum.[/EDIT]

I do have some question re the above quote, however. If it's true DC bias, it's frequency will not only be below 20Hz, but it will actually approach - if not actually reach - zero, right? Or am I off on that? And of course, that in itself is not humanly audible.

However, if the offset is strong enough to push the loudspeaker far enough from it's normal rest state, that can affect the loudspeaker's reprodcution accuracy, can it not? In that way, while the offset itself may not be audible, it's effect on the performance of the loudspeaker can be, can it not? Or have I fallen prey to another myth ?.

To the game...it's kickoff time.

G.

 

[masteringhouse]

I do have some question re the above quote, however. If it's true DC bias, it's frequency will not only be below 20Hz, but it will actually approach - if not actually reach - zero, right? Or am I off on that? And of course, that in itself is not humanly audible.

However, if the offset is strong enough to push the loudspeaker far enough from it's normal rest state, that can affect the loudspeaker's reprodcution accuracy, can it not? In that way, while the offset itself may not be audible, it's effect on the performance of the loudspeaker can be, can it not? Or have I fallen prey to another myth ?.

I believe all of the statements above to be true. My choice for 20 Hz was having to do more with the limits of human hearing and the range of most speakers rather than DC offset in an of itself. DC offset can rob you of headroom as well.

I do agree with Brad though that unnecessary processing should be avoided. If it's not a problem, don't use the "solution". The example I gave of filtering the snare was to solve one real problem (removing kick and rumble from a snare track) and one potential problem as described above. I wouldn't put a 20Hz filter on everything by default.

 

[ikon]

just ampliphy to 0dB and it should correct any offset...atleast does for me

 

[SouthSIDE Glen]

I do agree with Brad though that unnecessary processing should be avoided. If it's not a problem, don't use the "solution".

I also agree; that falls under two different general platitudes: Keep the signal chain as short as possible, and, If it ain't broke, don't fix it. .

That said, though, I do prefer to remove offset for the reason given previously; while it in and of itself may not be audible, it can have a detrimental effect on the ability of the playback loudspeaker to reproduce my mix with the same accuracy that it otherwise would without the offset, particularly on playback systems with drivers that may not be as robust as what I have in the CR.

I personally feel it's worth the signal chain "budget" to remove it and the plusses can outweigh the limited minuses involved in throwing a quality filter in on the bottom few Hz. But that's not something I'd chisel in stone. I can see a choice to leave it in, especially if it's only a tiny shift that puts no constraints on the dynamics.

And as to that last point, I have a Toshiba laptop with an internal soundcard that has a horrid offset, with an offset that rides somewhere close to a positive -15dBFS(!). Obviously not a soundcard I want to use for recording much of anything. But if one were forced to use a device with offset that bad, I don't think many of us would have a probllem dedicating a filter to correct that.

G.

 

[rayc]

AH. Penny dropped! Now I know why I had clicks at the beginning of tracks I thought I had so carefuly edited.
I use Waverepair to finish up my mixed tracks before burning (anything I didn't notice/couldn't fix in cakewalk) & since the author added a DC offset a few upgrades ago I've used it occasionally & on those occassions there've been fewer clicks.
I've also upgraded my soundcard & some of the chain so I may have eliminated the cause somewhere along too. It's nice to know what the prob was/is related to.
Thank you gentlefolk for this elucidating discourse.