Is it really necessary to remove DC offset? -Sound Forge - PC

Sound Forge - PC

Subject:Is it really necessary to remove DC offset? Posted by: msterlin Date:8/12/2003 3:56:46 PM I've been ripping CDs, removing DC offset, and (peak) normalizing the tracks. Now I am wondering about DC offset. Everything I've read says that DC offset results in inaudible distortion, but it is a good idea to remove it if present so that any subseqent processing you do works on a "correct" waveform. What I've noticed though is that after removing DC offset, the level meters will hover at a given level at the end of a song, rather than fade nicely to silence. Should I fade the ends so the song fades out to near silence (-90dB on the SF meters) at the end or is this really irrelevant? I think it would matter if the level were in the audible range (say -30dB) but probably doesn't matter since it is usually much less than that.
Subject:RE: Is it really necessary to remove DC offset? Reply by: Chienworks Date:8/12/2003 4:20:19 PM Worst case scenario: having a DC offset means that you are constantly driving the output stages of the power amplifier with an unnecessary DC bias, using more energy, making the output transistors run hotter, drawing more electricity, causing the power company to burn more fossil fuel, wearing the amp out sooner, adding to the rubbish heap faster when you throw it away, causing the factories to have to use more raw materials and energy and thus burning of more fossil fuels, adding to the pollution and carbon dioxide content of the atmosphere, speeding up the greenhouse effect, raising the temperature of the atmosphere, causing the amplifier to run even hotter and accelerate the process, and eventually turning the planet into a smoldering, poisonous, uninhabitable dump. Mind you, that's the worst case. ;) Most of the distortion will be subaudible, but it is measurable. What's probably happening is that these tracks had some DC offset before being mastered and in the mastering process the subsequent processing caused the DC level to change from moment to moment throughout the song. When you have SoundForge remove the offset it removes a constant amount. This means that you've probably altered the offset rather than removed it. This would be especially noticeable in sections where the track was faded (e.g. the end) during the mastering process. Since there was less offset during the fade, removing a constant offset may actually have introduced a larger offset at the end of the song. Fading after removing the offset can help. Is all this necessary? Probably not. After all, if you see the offset when you originally rip the track then it was there when you played that CD to begin with. It probably didn't interfere with playback then.
Subject:RE: Is it really necessary to remove DC offset? Reply by: msterlin Date:8/12/2003 5:27:47 PM Thanks for the explanation ChienWorks. As usual, you're very helpful and I thank you for your time. I'm glad I've been removing DC offset - don't want to be responsible for the premature destruction of the planet. :) While we're on this topic, what exactly do the numbers mean when you do statistics? I think there should be the same number of samples above and below the zero crossing. If it says -5 for left channel and 2 for right channel, does that mean 5 fewer samples below the zero line and 2 more samples above the zero line? Are really large values indicative of a poorly mastered CD? Ozzy Osbourne - No More Tears was way out of line with the rest of my CDs (-4000 in one channel and 500 or so in the other). It sounded fine to me, but after seeing small numbers on others, that was kind of shocking.
Subject:RE: Is it really necessary to remove DC offset? Reply by: Rednroll Date:8/12/2003 6:57:14 PM Chienworks, great explanation!!! I'm envious, I couldn't have said it better. Good luck with the rest of the responses on this one. :-)~
Subject:RE: Is it really necessary to remove DC offset? Reply by: msterlin Date:9/2/2003 11:46:47 AM So would either of you (Chienworks or Rednroll) like to follow up on this topic? I'd really like the opinion of those with more experience on this topic than myself. Bottom line: If you were ripping your cds to wav files and want the best quality would you bother removing DC offset if SF statistics indicate it is present or is there nothing to be gained from doing so? Also, given that (good) recording studios/engineers supposedly work with properly calibrated high-end equipment, does the fact that a cd has huge values for dc offset say anything about the equipment and/or skills of the recording engineer?
Subject:RE: Is it really necessary to remove DC offset? Reply by: Rednroll Date:9/4/2003 11:57:24 AM "Bottom line: If you were ripping your cds to wav files and want the best quality would you bother removing DC offset if SF statistics indicate it is present or is there nothing to be gained from doing so?" Bottom Line is do you have ears? If so, then try using the DC offset remover and see if you notice any quality improvement. I'm 99.9% sure that you won't, but It's pretty easy for you to find out for yourself by removing it, and then doing an undo. Thus, doing an A/B comparison. Also, what do you consider as a "huge" DC offset? The DC offset remover tool really does not apply for what you are using it for. You are digitally extracting audio from a CD. Thus, in this process there is no DC offset added within doing this process. DC offset usually happens when you are transferring audio from 1 analog Device to another. The DC offset gets added to the audio signal by the electrical components they travel through, mostly due to bad capacitors or bad grounding between 2 analog devices. Sonically, you probably can not hear DC offset. The side effect of having DC offset is that you won't have as much headroom as otherwise achievable. It will also cause additional wear on the devices they are playing through, because there is power being generated unneccessarily, yet you are not hearing it.....please refer to Chienworks explanation for further details to global warming. In what you are doing, I would expect the DC offset to be very minimal, and as Chienworks previously described if Sound Forge dectects it, and you digitally extracted the audio, then it was there to begin with. Which means, that Ozzy Osbourne's mastering engineer, probably already observed it, and probably conscienciously already made a decision to leave it in there because it wasn't that bad to run the audio through yet another process. So if some how you think you have some tricks over Ozzy's mastering engineer, I'm sure he would be interested in hearing them. Which brings me to the next point of why you shouldn't be removing it. Any process, you do to audio further adds DISTORTION...most mastering engineers already know this, and try to do the minimal amount of processes to reduce the added distortion....thus why their maybe a little DC offset....but not "huge". red
Subject:RE: Is it really necessary to remove DC offset? Reply by: msterlin Date:9/4/2003 3:48:11 PM 1. Yes I have ears, and no I cannot hear any difference as I stated. I'm not the kind of person that posts questions without having tried all the options first. 2. A "huge" offset is relative to others. Most cds have dc offset less than 10, so 4000 for Ozzy is "huge" relative to 10. 3. I know the dc offset was there to begin with if I rip the track from a cd as ripping doesn't change the waveform (although it may not be exact due to reasons I'm sure you are aware). 4. I understand dc bias adds unnecessary power that makes a device work harder although it is so miniscule that it doesnt matter one bit. 5. The fact that Ozzy's recording engineer "made a conscious decision to leave it in there" means absolutely nothing. Are you implying that all recording engineers have equal levels of knowledge, skill, and experience? I have no tricks, I am a software engineer with an interest in music and come here to try to learn more. 6. So the bottom line is simply that dc offset is inaudible distortion, removing it may add more inaudible distortion, and the point is moot. I didn't mean to offend either you or chienworks by asking a question that you seem to feel is stupid, although i think its ironic that you never tire of answering "how do I remove the blue from the green paint" (remove vocals).
Subject:RE: Is it really necessary to remove DC offset? Reply by: Rednroll Date:9/4/2003 9:14:55 PM I'm sorry, if you got offended by my reply. It wasn't meant to be offensive, just informative. If that wasn't what you got out of it, then I'm sorry. I'll step aside and let someone else answer your question.
Subject:RE: Is it really necessary to remove DC offset? Reply by: Daave Date:9/5/2003 5:50:00 PM WOW .... this is perhaps the best Q&A thread I have ever seen on this board .......... I have often considered the same concepts that mstrlin has in question and all of a sudden I feel I have learned some stuff via chien n red .. thanks .... mebbe SF should put this one in the FAQ ...... it is worthy ... OH YEAH ...... msterlin ------ no need to suck up to red ........ often he has great suggestions but when he gets out of his league he always says something to the tune of 'don't you have ears newbie ...... listen up n someday you will be like me way up here on top' haaaaaaaaa like when ya have a question in physics class n the teacher says 'don't ya have fingers to count on moron' instead of coaxin ya along towards the solution .... er mebbe sayin 'ya got me right now .... but I will have the answer tomorrow' great questions mstrlin ....... sorry I had to pick on ya a tad red ... but ... it was in a smiling way
Subject:RE: Is it really necessary to remove DC offset? Reply by: sk Date:9/6/2003 11:59:43 PM Hey, msterln. Good question; good thread; just ignore Rednroll for the most part when he's on his little pedastal. Don't let him ruin the rest of the forum for you. He will, if you let him. Just don't let him. sk
Subject:RE: Is it really necessary to remove DC offset? Reply by: MJhig Date:9/7/2003 9:49:55 AM OK, I have to take up for Red on this one. Sure he (and myself) have been sarcastic in some replies in the past but I don't believe that's the case here. I think he was trying to offer genuinely helpful information. I'm originally from New England, a region that's notorious for blunt, direct, no kid gloves matter of fact-ness, I see this method/persona in pretty much all of his posts and even in the genuine attempts to be helpful this method can be misinterpreted by many as "smack-down". I had a terrible time myself avoiding pissing people off when I moved to southeast US where diplomacy and "don't make waves" carries the day. In this case I believe Red's guilty of his history and non-diplomatic nature not belittling the OP. MJ
Subject:RE: Is it really necessary to remove DC offset? Reply by: sk Date:9/7/2003 11:05:59 AM It's funny. The more I see tripe apologetic crap passed off as reason, the more reason I have for knowing I was right on the mark in the first place. Thanks, mjhig; it's like shooting ducks in a barrel sometimes. "Garbage In = Garbage Out". (At least try to adhere to your own sacred principles.) sk
Subject:RE: Is it really necessary to remove DC offset? Reply by: MJhig Date:9/7/2003 4:21:50 PM >>>>(At least try to adhere to your own sacred principles.)<<<< I can guarantee you I do and will. I've never defended Red before, in fact he and I have butted heads in the past. The truth is, right is right and in this case (and a few others) I believe he is being unjustly accused of bitch slapping. When he is nasty there is no shortage of posts pointing that out, conversely I felt compelled to stand for what I feel is right in this case as it appears he is getting piled on. That's all there is to it. If I disagreed with him or anyone, I would not defend them. MJ
Subject:RE: Is it really necessary to remove DC offset? Reply by: captn_spalding Date:9/7/2003 6:25:06 PM Now let me get this straight: "msterlin" asks a question. "Chienwoks" gives a concise, lucid answer. "msterlin" asks "red" (and others) to tell him more. So "red" does. And somehow this makes "red" the bad guy?? If you can't stand the heat, stay out of the sudio!! And what did "red" say that was so bad? -use your ears to judge sound!! Now thats great advice!! If you were preparing a wonderful dinner, would you use a gas-spectrometer to tell you if it tastes good? No, you'd use your mouth!! In the wonderful documentary "standing in the shadows of motown" one of the funk brother drummers (sorry i forget which) says the best bass drum he ever had was an old cardboard beer case. Now, how did he make that judgement? By using his ears!! Red, you don't need me to tell you this, but I will anyway -- Screw their hurt feelings, keep bringing people back to reality. ..spalding
Subject:RE: Is it really necessary to remove DC offset? Reply by: Chienworks Date:9/7/2003 7:34:29 PM LOLOL!!!!!! Is "Chienwoks" anything like "Ewoks"? Is that why i've been getting furrier in my old age? ;) I've seen Rednroll be abrasive from time to time and even downright unpleasant now and then. It's not my style and it does grate on me. However, he usually does give useful information. In fact, i've seen a trend lately that he is being more considerate and friendly. I've even seen him apologize when people have complained about his style or felt offended. Overall he's improving a lot and i for one would like to encourage him to continue. Thanks Red! :)
Subject:RE: Is it really necessary to remove DC offset? Reply by: msterlin Date:9/7/2003 7:55:13 PM Since I started this mess, let me say what I got out of it and how I feel about the whole thing. I asked a question about dc offset in an effort to better understand the issues. I got a good response from Chienworks which did help me alot because he explained that the dc offset isn't constant and may have fluctuated from moment to moment thus leading to the behavior i noticed of the level meters hovering at the end after i removed it. He did say that I could fade the ends if it bothered me, but likely it wouldn't matter. That confirmed what I thought and i was thankful for the response. I thought the whole global warming thing was a bit much, but after reading these forums for a few months i've seen that he is usually pretty informative and never resorts to language that would make one feel stupid for having asked such a question - I took it as simply a tongue in cheek remark and was not offended. I asked Red to follow up because I know he is also well informed on these issues and because he replied, but not to my question. Instead he simply said "great job chien, couldn't have said it better myself - good luck on the followup". So why not follow up instead of just patting oneself on the back? I thought, perhaps mistakenly, that it was an interesting question and people might like to explore the topic a bit further. As I see it, the problem is the follow up was not so much about my question of why dc offset would be there in the first place if a good recording studio/engineer has properly calibrated equipment, but why would I dare question the recording engineer. So instead of offering an opinion on that (which could have been as simple as 'Hey it happens, and here's why it shouldn't matter...') I got what appeared to be a lecture on how all engineers always do the right thing and by the way didn't chien already answer that. As I said, he answered my first part, which led to more questions, and i hoped for more opinions. I understand that some people aren't aware of how their written words can be interpreted and for all i know, Red didn't really mean it to sound condescending (and he said he didn't). Although, the phrase "Well you have ears don't you" should have been phrased "Well in this case, you should let your ears be the judge". Then go on to explain the fact that you will have slightly less headroom available (I got that out of his post) but in all likelyhood it won't matter enough to worry about. I was really just looking for what people with real experience with digital audio would consider "best practices". To me, the fact that I can't really hear any difference between a file with dc offset and one without doesn't tell me all I need to know about quality. I can't smell carbon monoxide, but the fact that I can't smell it if its present doesn't mean the air quality is good enough (in fact it could be deadly). I was just wondering if dc offset really should be removed (everything i had read said yes) so that when i later transcode these wave files to mp3 or another compression format I will be starting with the best possible source. So, Red I am not offended and I hope you will continue to offer your thoughts when asked, maybe just try to write more neutrally. I'm glad I found this forum because I have learned quite a bit and hope to learn more - but be advised that when i do ask questions, they will be more along the lines of this one and not the kinds that can be annoying to you veterans because they have been asked and answered so many times (remove vocals, mp3 loops, record what you hear, etc).
Subject:RE: Is it really necessary to remove DC offset? Reply by: Goldenears Date:9/8/2003 1:57:40 AM In the best of all scenarios there should be no DC offset. Apart from causing the output of DC coupled audio amplifier chains to be similarly offset, and therefore wasting energy and slightly upsetting the output device's bias and marginally increasing that device's distortion, you are probably never going to notice the problem. However, if you are compiling a CD from multiple sources, regardless of the format involved (.wav .mp3 etc.), and there are different degrees of DC offset from each of the sources AND they are edited together in a seamless transition, you run the distinct possibilty of creating an audible click at the edit point if you do not remove the DC offset before you edit them together. If you are working with highly compressed audio with high audio level at the commencement of each track you will probably never hear the click, however if you are working with large dynamic range (eg. classical) material that commences and ends near the studio noise floor you will probably hear the edit as a click, IF the DC offset is any more than say 60dB lower than peak level. Having lost a week of classical music editing time in the early days of CD recording post production whilst a DC offset problem was tracked and repaired in a commercial studio's editing equipment taught me how important the absence of DC offset can really be. Happy editing, Goldenears
Subject:RE: Is it really necessary to remove DC offset? Reply by: Rednroll Date:9/8/2003 8:16:54 AM msterling, As pointed out, my statement about "having ears?", was not meant to be an insult? You asked which, would give you the best "quality". To me, quality means you can hear a difference. Thus CD's have better quality, than cassettes, DVD better than CD, all of them better than vinyl. So my point was to lead you in that direction of trying it for yourself and letting us know what you hear. You will learn a lot more through your own experiences than I could ever teach you in these forums. Then I went on to explain the technical aspect of DC offset so that you could better understand it, and why it didn't apply in what you where doing. I appologized if you took offense. If I was trying to be insulting to you, you would have known it. I don't dance around with subtlties. I think you're reaction to my reply was a little over the top for someone looking for information. In the future I will be very reluctant to offer any advice to someone like you. If you're a software engineer then maybe I'll have to talk to you in IF_THEN_ELSE statements so you won't take offense and misinterpret my response and then have other users join your whining game. I've spent many years learning about audio and have many more years behind it in experience. I don't get paid for answering posts in this forum, yet you expect me to offer you help and answer in a polite, politically correct manor free of charge? Hey!!!! Go F*@k yourself, I don't owe you anything. You can open the books and pay for an education just as I did. From your original question I can tell you truly don't understand what "DC Offset" is. I was going to further give you some information of how to create DC offset and give you some steps to better understand it. This will go much further than going by a "best practice". With your rudeness of telling me, how to reply, when to reply, and to ensure that I don't offend you, I have no desire to offer any further assistance to you. IF username=msterlin; THEN reply=smartass remark; or; reply=ignore; ELSE reply="informative response='ANSWER'"; END
Subject:To all those NOT Rednroll Reply by: sk Date:9/8/2003 11:42:29 AM Again, to all of those NOT Rednroll, I think you missed the point of what I was trying to say. While you continue to make excuses for his inexcusable actions, just LOOK at his reply from 9/8/03. He has obviously learned NOTHING as far as his incessant, patently offensive comments and attitudes are concerned. He has, whether or not you care to acknowledge it, ruined the SoFo board for a number of potential active members who have left merely to not have to put up with his crap. And so the situation continues, whether or not you make excuses for him or not. You all are obviously very intelligent people. Just open your eyes and ears a bit, and try to see the bigger picture here. Whether or not "he's gotten better', and whether or not he offers valuable information, is not the point. I acknowledge that he knows what he's talking about FROM HIS OWN, ONE DIMENSIONIAL, "MY WAY OR THE HIGHWAY" LIMITED PERSPECTIVE. The questions are whether or not it's worth putting up with his obnoxious offensive behavior in the process, and how much is lost by way of potential members refusing to frequent this forum as a result. Ultimately we may never know what is gained and what is lost in having to constantly sift through his crap just to get to whatever it is that he might or might not have to offer. But just look at the difference between Goldenears' remarks and those of Rednroll. It's so totally night and day that you would have to be blind, deaf, dumb, and dumber not to see/hear it. If Rednroll only wants to interact with other audio engineers, then let him start his own expert forum "FOR AUDIO ENGINEERS WHO ASK THE TYPES OF QUESTIONS I CONSIDER LEGITIMATE" and be done with it. This is obviously NOT that type of forum, and he has no right to impose that sort of expectation. Yet he DOES do exactly that, over and over and over again. The reason I didn't even bother to address this to him is because he's demonstrated on countless occasions his total inability to see his own actions in any objective, constructive way whatsoever. But I was hoping that other, more reasonable members, who have just as much expertise as Rednroll, but with a lot more personal skills, could once and for all confront him and issue HIM an "IF/THEN/ELSE" ultimatum. Then maybe he might take the need to re-examine his own actions more seriously. But as long as that does not happen, he's obviously content to continue steamrolling his way just as he's done so many times in the past. Merely saying that "Well, he wasn't NEARLY as offensive THIS time as he's been in the past; see, he's getting better", etc., is just not acceptable. All it does is further reinforce for him the misguided notion that he doesn't have to change. In cliched pop psych 20th century jargon, you end up unwittingly enabling him and feeding his misguided notion that everything is just fine, when it obviously is not. There is a rather famous saying (roughly paraphrased): "Evil does not proliferate in the world because evil men intentionally set out to do evil; it flourishes because good men see evil, then sit back and do nothing." I sincerely think it's time for the more seasoned members of this forum to stand up and call a spade a spade. Maybe then he would finally knock off all the crap and stop trashing this board. Maybe not, I don't know. He obvioiusly will never listen to anyone he considers to be below himself, and so as long as the more experienced members refuse to hold him accountable, he will just cointinue to do what he has demonstrated over and over again to be his "habit". Personally, I don't think anyone coming here to this forum should have to be blasted by him; especially when there are many other experienced members here who do NOT behave the way he does. What I suggest is that you consider the following example: Anyone who has ever moved next to something noxious, like a railroad track, or a noisy highway, experiences a certain transition process. Initially, the noise is overwhelming, but eventually, it's barely noticed. I believe that something similar has happened here with regard to the reactions of some of the more experienced members. However, I do not believe the solution in this instance, as opposed to actually living next to a railroad track, is to simply wait around long enough for the noise to blend into the background; I believe it's time to reroute the train. sk
Subject:RE: To all those NOT Rednroll Reply by: Rednroll Date:9/8/2003 12:17:41 PM Hey SK, You made 3 posts in this thread already. Where's the information to go along with it? Oh....you're the moderator or is it dictator? Sorry, I don't live in a dictatorship, and have been educated in U.S. schools, which requires a knowledge of history and of the Bill or Rights. If you're not familiar with it, then here it is for you: Amendment I "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances. " When you come in here and offer nothing but a personal attack on me, you can bet I'm going to exercise amendment I and defend myself. Obviously, there was a misunderstanding with my reply and I apologized for it. Somehow, you missed that completely with your viewpoint. When I start to live in a bubble like yourself with blinders and personally leave a forum because someone's viewpoint or the way they express it upsets me, then I certainly would hope someone else to do me a favor and exercise Amendmant II and put me out of my confined misery. Amendment II "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed. " If anything is not welcomed here, it's someone that singles out an individual and personally attacks them, yet offers no educational information along with it. This is an Audio forum, why don't you offer some Audio information for once? Nobody, comes here to read your viewpoint of an individual. If you think they do, then why don't you take your own advice and start a forum of your own, which does nothing but singles myself out and expresses YOUR VIEWPOINT. Thank you, Have a nice day :-)
Subject:RE: Is it really necessary to remove DC offset? Reply by: msterlin Date:9/8/2003 12:40:47 PM Thanks Goldenears, that's the kind of perspective i was looking for.
Subject:RE: Is it really necessary to remove DC offset? Reply by: msterlin Date:9/8/2003 1:09:12 PM "I don't get paid for answering posts in this forum, yet you expect me to offer you help and answer in a polite, politically correct manor free of charge? Hey!!!! Go F@k yourself, I don't owe you anything." I don't expect* anything from you and i was certainly not over the top. Contrast my response with yours: I took the high road, did not attack you, and even gave you the benefit of the doubt by saying i didn't think you meant to be abrasive. Clearly I was wrong about that. I read these forums for a few months before ever posting and my first impression of you was that you are arrogant and abrasive. I can see from all the followup posts that that view is definitely in the majority. Notice that I didnt directly address all the posts aimed at you even though i agreed with them. But now, I must state emphatically that you truly are a pompous, arrogant and generally disagreeable person. sk has you pegged to a tee! You are right in that you don't owe me or anyone else anything, but then why do you bother to post at all? The whole Bill of Rights thing was comical. You are basically saying that you have a constitutional right to be obnoxious, and indeed you do; but eventually people tire of it and will tune you right out. As for me, I will continue to ask my "dumb" questions as there are definitely people here with the knowledge to help me learn more over time and are willing to share their knowledge in a friendly, non-confrontational manner - sadly that doesn't include you.
Subject:RE: Is it really necessary to remove DC offset? Reply by: Rednroll Date:9/8/2003 1:33:15 PM "I didn't mean to offend either you or chienworks by asking a question that you seem to feel is stupid, although i think its ironic that you never tire of answering "how do I remove the blue from the green paint" (remove vocals)." You didn't say this? Where did I ever say your question was stupid? Why did you feel it necessary to throw stones at me? I think you assumed too much and interpreted my reply as you wanted too, instead of how it was intended. Chienworks, started with a good reply, which was humorous yet informative. I was enjoying the humor in it. Somehow you singled me out then, and felt I was obligated to give you a reply. Seeing that Chienworks opted not to give you a reply, I decided to help you out because you singled ME out and I saw your question wasn't fully answered. How about this? "So would either of you (Chienworks or Rednroll) like to follow up on this topic? I'd really like the opinion of those with more experience on this topic than myself." And that's what I did.....you took offense on how I presented that information. No thanks from you......just criticizing me for the information because, again you misinterpreted it as an insult. There's 3 other posts from other users that pointed this misinterpretation out to you, along with an apology from myself. What else do you want? The only thing you've done is bite the hand that feeds you after you where asking me directly to throw you a bone. Now you're wondering why I take offense? "As for me, I will continue to ask my "dumb" questions" Again did I call your question dumb as you're assuming?

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