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Probably a dumb question (DC offset)

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heathen:
In the attached image, is the part circled in red DC offset?

bombdiggity:
DC offset deals with the entire segment not a tiny segment of it. 

"DC offset is a mean amplitude displacement from zero. In Audacity it can be seen as an offset of the recorded waveform away from the center zero point. DC offset is a potential source of clicks, distortion and loss of audio volume."
 
DC offset - Audacity Development Manual
manual.audacityteam.org/man/dc_offset.html

There's a dramatic illustration of what it could look like there ^. 

Gutbucket:
That image shows a plot of voltage over time, with the change in voltage representing pressure variations. See how the area you've circled undulates above and below the zero voltage line?  The center of undulation indicates the average voltage value.  If that center value was constantly above or below the zero voltage line over the entire length of the file, it would indicate the presence of DC offset.  A recording system intentionally sensitive to zero-hertz pressure variations acts as a barometer.  Since audio recording systems are designed to measure pressure variations only in the audible range, with a sensitivity that intentionally drops off to nothing before reaching zero hertz, significant DC offset in an audio recording system indicates something may be incorrect in the signal chain.  Or that Jimmy Cliff is in town.

bombdiggity:
Great breakdown (as usual) ^. 

I've noticed that certain pre's have a defined DC offset.  For example my Tinybox runs at .03% every time and always has.  My Oade modded R-44 always exactly at 0%, running the same mics (the only other difference in the chain being the cables).  I can't say I hear anything amiss with the sound of the Tinybox though I always correct it in editing. 

Old analog sources (like cassettes) transferred to digital tend to show much larger DC offsets.  Sometimes different offsets in each channel.  Cassette recordings almost always have an offset. 

Some instruments will appear to have much greater energy above the zero voltage line than below (mostly brass ones) and it can look to the eye like the recording would have to have a large offset but when you check the stats it doesn't. 

It is easy to get a read on it just by pulling the stats on a file in your editor and easy to correct.  See the other recent thread about correcting in Audition. 

heathen:
Thanks for the info guys.  Bottom line: is the above anything to worry about?

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