A run on sentence(question???) about DC offset

Discussion in 'Mastering' started by DrGonz, Sep 13, 2007.

  1. DrGonz

    DrGonz Active Member

    So I am assuming that DC offset occurs due to processing errors. Like I am thinking now to render each separate track and try to pinpoint which tracks contribute most to the offset. I am wondering if processing a track through, like say, soundforge or wavelab is a good idea, as to remove DC offset of an individual wave file.

    I also wonder about DC offset and what it really effects/what causes it? I know that when you mix a song and then start mastering it is wise to first commit DC offset removal to the file. Is it cuz DC runs on a volts basis and AC measures it digitally.??? So basically digital understands the electrical energy of a signal as a less accurate digital representation. Whereas in analog recording the electrical energy is defined by a voltmeter. So I am asking if DC offset occurs due to error in the signal electrical path, that it could be related to the power source and how dependable that power source runs.
    Not sure if this makes any sense at all!! But just had to ask lol
     
  2. Michael Fossenkemper

    Michael Fossenkemper Distinguished past mastering moderator Well-Known Member

    DC offset is mostly due to broken gear and bad A/D converters. Bad or cheap converters will leak DC voltage into the signal. Gear like keyboards can leak DC into the signal too. Sometimes lots of sub freq's will "trick" the analyzer into thinking that there is DC in the signal when in fact there is not. DC used to be an issue, not so much these days unless you are using old questionable gear.

    Another sign that there is DC in the mix is to hit play and start in the file. If you hear an odd pop, that might be a sign that you have DC offset.
     
  3. DrGonz

    DrGonz Active Member

    That all makes more clearer sense to me now thnx.
    One other quick question then..... could the wall outlet that has either poor power or something wrong w/ it add to DC offset problems?
     
  4. Zilla

    Zilla Active Member

    If you were to measure a wide variety of equipment (even new/hi-end) you will find a great deal will not be sitting exactly at 0V. They will have some amount of DC offset. The issue is really how much offset. A few millivolts is not unusual or harmful. A few tenths will start to reduce headroom. Anything greater will likely cause surrounding circuits to misbehave in unexpected ways.
     
  5. Michael Fossenkemper

    Michael Fossenkemper Distinguished past mastering moderator Well-Known Member

    IMO, if there is that much DC in a new piece of gear's signal, then it's broken or very badly designed and should be returned. I've noticed over the last 5-6 years that the amount of DC in mixes is pretty much a non issue. When I do get a mix that has a problem, it's almost always because of a funky keyboard.
     
  6. Zilla

    Zilla Active Member

    How much DC is "that much DC"?
    Please quantify in volts or bits.

    I can name a good quantity of excellent sounding devices which will measure some offset when connected in a real world audio chain. Devices that people covet in these very forums. This does not mean they are badly designed. Perfect DC offset is not the be-all-end-all parameter for design quality judgments. Again, it is the magnitude of offset that counts. What would you consider to be an unacceptable amount?

    That stands to reason. More people are mixing/processing in the box now. Software does not have the same physical issues that hardware circuitry has (bias, poor grounding, temperature drift, etc.) Therefore less offset problems should be in evidence in mixes.
     
  7. Michael Fossenkemper

    Michael Fossenkemper Distinguished past mastering moderator Well-Known Member

    Too much is... If you have to get rid of it. It's pretty easy to design a circuit to eliminate DC. If it's leaking into the chain to a point that it's a problem, then something isn't working right. The tiny amounts that are common in lots of gear isn't an issue. It's when you see your drivers poke out when you play a file, it's an issue. Some people mistake phase rotation as DC offset. it looks like the waveform is out of balance but it's totally natural to occur in lots of things.
     
  8. Zilla

    Zilla Active Member

    The basic point I am making.
    That's an obvious symptom. Readers here might be interested in a discussion of the not-so obvious ones.
    Yes. But rather difficult to design one that does not negatively effect the fidelity of the audio circuitry it is protecting from drift.
     
  9. Zilla

    Zilla Active Member

    If you are referring to 110V AC mains, then its possible that faulty wiring or grounding may cause problems. For example, let's say a mic pre and a converter are plugged into separately located wall outlets and their grounds are at different dc potentials because of faulty wiring. In this scenario there could be an offset between the two boxes which may leak into the signal path.
     
  10. DrGonz

    DrGonz Active Member

    Hey Zilla,
    So lets say I have an amp in a corner of my studio and its plugged into a wall outlet. In another part of the room is my DAW and it is plugged into a separate power outlet. I mic my amp but that should be fine still, since its not a DI connection. I am also wondering if the wall outlet has a good ground for the guitar head in my studio, better look at it too. Thnx for the responses really interesting posting going on.
     

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