Newbee question about DC offset...What is it?

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Mbira

Well-known member
Joined
Jun 4, 2004
Messages
2,422
Location
Austin, TX
Can any of you guys explain (or post a link) explaining what DC offset is in laymans terms? The articles I've read on it get into even order harmonics becoming greater that odd order thru processing of audio-and then I just get lost.

Does CD offset relate just to audio signals for our purposes, or is it also an issue with power supplies? When somebody has a "cleaner" power supply, do they mean there's less DC offset?

Let me see if I'm right...If you have AC and it goes thru a bridge rectifier and then only one cap (per polarity), would the DC fluctuations that you still get be DC offset?

Thanks for the newbee help!!!
Joel
:guinness:
 
As I understand it, DC offset is when an AC signal has a DC component. In digital audio it will lead to lower headroom.

In a transformer balanced output curcuit it will magnetize the transformer, unless it is gapped like the Neve.

dcoffset.gif


Also here is a link in regards to digital audio
http://www.sweetwater.com/insync/word.php?find=DCOffset

I hope this is correct, and that it made some sense.

Steven
 
I think of it as being any residual voltage at the output pin of an opamp.
Leta say you have a single supply opamp with one input pin tied to ground via a resistor.
The output pin should have zero volts on it.
In reality, there is a very small voltage at the output of most opamps.
This voltage can be trimmed sometimes with a trimer circuit.
Opamps over the years have been getting this offset voltage closer and closer to zero.
In the old days, it was measured in millivolts.
Now, it is quite common to see opamps with just a few microvolts of offset.
API, Melcor, these are just opamps also, anfd they too have the same type of dc offset.
hope this helps!
cj :guinness:
 
Thanks guys, so how and when does the offset become a problem? So how are you also adding offset when processing audio say in Pro Tools, and how do you take care of it?

Joel

and a big :guinness: for each of you.

Joel
 
DC offset in digital audio occurs at the A/D converter. It's ususally not a problem for me but if can use the audio suite DC Offset plug that comes with PT.

If you are building a mic pre, a film cap is used to block the DC before it hits the transformer.

Steven
 
Hmm...OK. This link I read:
http://palimpsest.stanford.edu/byform/mailing-lists/arsclist/2003/03/msg00161.html

Confused me into thinking that actual manipulation of audio once inside the program can affect the offset value, but I see now that I read it wrong. So does the offset sound like rf?

OK I'm done now,

Joel

Thanks again for the clarification! :guinness:
 
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