dc offset ???

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DAS19

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I dont think many people including myself understanding or have heard of dc offset can those of you who know about it please let me know what it is? and what I can do to prevent it/stop it?

I am pretty sure it has to do with recording levels coming in to your mixer and the extra headroom you leave if you dont record it as loud as possible it will really effect your mix? correct me if im wrong.
 
DC offset more often than not is caused by faulty gear somewhere.
Some how DC voltage is getting recorded to your medium.
Usually gear is supposed to have a DC filter of some sort at the output (capacitor, op-amp, transformer, etc..). Some gear have DC filters at the input too. But usually not recorders, since they are intended not to color whatever it is that you are recording. Who knows, you may want to record DC voltage for analysis purposes.
Plus the less DC coupling, the better for sound quality.

Once you record it getting rid of it is pretty simple, all you need to do is put a subsonic filter on your audio such as a 24dB / octave filter at 20Hz.

But it is best to find out why you have that DC voltage present on that track. Exactly what piece of gear is causing it. Sometimes mixers can pass DC voltage, so it may be what is feeding into the mixer.
 
DAS19 said:
I dont think many people including myself understanding or have heard of dc offset can those of you who know about it please let me know what it is? and what I can do to prevent it/stop it?

I am pretty sure it has to do with recording levels coming in to your mixer and the extra headroom you leave if you dont record it as loud as possible it will really effect your mix? correct me if im wrong.
Click to expand...

Man is this a long road, but, DC offset is mainly the amount of DC that is injected into the ADC AC signal. The amount that the AC signal is raised or lowered (skewed) from a 0 crossover point. Too much DC offset introduces a "mock" 0Hz frequency (which normally you would not hear) and cuts the headroom the higher it goes. Originally in analog the "0Hz" being introduced would cause hum because there was actual 0Hz current being injected into the analog signal. In digital, this "0Hz" reference dose not truly exist as there is no current injected, but the whole signal is offset in binary numbers as a result of the conversion amplifiers.Think of taking the whole signal and moving it up (or down) and you get the idea. DC offset usually is from the ADC amplifier and means that the bipolar signal is offset in one direction. So, a decent amp will run +/- 15vDC rails and the signal ideally will ride exactly the same voltage in both directions. Like between +5, 0, -5. A DC offset could be more like +5.5,.5,-4.5 (converted into binary words!) where the DC offset would be .5Vdc. DAC converters are usually designed to remove and correct DC offset.Some souncards have a setting for DC offset correction. A common confusion is with a signal that is asymetrical (like the human voice) being labeled as DC offset. You can tell the difference in a wavefile editor. So DC offset is generally undesirable, and removing it is generally a good thing to do (if you can't eliminate it at source).

Did I lose you? If I did, maybe others can explain it better.

Good Luck!
 
MCI2424 said:
A common confusion is with a signal that is asymetrical (like the human voice) being labeled as DC offset.
Click to expand...
Yeah that is important to note. Just because the wave form tends to go for the + or - side, does not mean it has DC offset. Kick drum, vocals, and horns are notorious for doing that. But just about anything can cause an asymmetrical wave form.
If you're in doubt. It's won't hurt to try a DC filter. If it doesn't change with a DC filter, just revert back to the unfiltered version.
 
DAS19 said:
I am pretty sure it has to do with recording levels coming in to your mixer and the extra headroom you leave if you dont record it as loud as possible it will really effect your mix? correct me if im wrong.
Click to expand...

Not exactly. Audio signals are AC, or Alternating Current. Think of a sine wave. DC is not a sinewave. It is just a straight current. It does not belong in audio signals but exists in electrical circuits. so if DC bleeds into your audio signal the voltage of that signal will create an "offset" because that voltage will add to the voltage in your audio. The reason that a low frequency filter was suggested is because you can imagine the DC as being a 0Hz frequency. At least all of this is my own understanding.
 
"When transitioning between two pieces of digital audio, one with an offset and one without (or with a different amount of offset), there will be a pop or click at the transition point. "

just read that whihc is an answer to one of my problems. which also means i have had some dc offset in my audio.

this article also states that most programs have a dc offset correct button that you just click and it fixes the offset. so maybe ill just use that unless it messes with the quality?
 
DAS19 said:
"When transitioning between two pieces of digital audio, one with an offset and one without (or with a different amount of offset), there will be a pop or click at the transition point. "
Click to expand...
Well there are otherreasons that audio will pop at transition points. Most commonly it's because the audio was cut at a non-zero crossing.
So, if you apply a DC filter, and you still have pops, zoom in real close at the transition. See if any of the waves are cut-off at any place other than a "0" crossing. i.e. the waveform should be right on the center line at the point of the cut.
DAS19 said:
this article also states that most programs have a dc offset correct button that you just click and it fixes the offset. so maybe ill just use that unless it messes with the quality?
Click to expand...
It shouldn't really effect the audio. It all depends on how they go about correcting the DC offset.
 
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