Bass guitar modulating waveform/varying DC offset?

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mattplaysguitar
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2012/04/21 02:16:52 (permalink)

Bass guitar modulating waveform/varying DC offset?

Take a quick look at this image of a bass track I just recorded:

http://www.mattlyonsmusic.com/images/Bass_Waveform.jpg

It's a cheapo eBay bass, running through a Zoom GFX-5 guitar pedal, into an Edirol UA-25ex. I only have some light compression enabled on the Zoom. I don't have my OctaBass in use here (it's connected, but bypassed - and supposedly has 'true bypass').

Now, I will be planning to master this fairly loud. So I'm looking right back to the start of things so I can reduce issues in the future. Anywho, this 'variable DC offset' or whatever is going on in some of the notes may hit me a bit. Looking at it, you can see the positive part of the waveform is pretty flat and well compressed. The negative is almost uncompressed looking. There is a very distinctive trend going on here. I'm just wondering how you would approach something like this to fix it. Will the right compressor do the trick? Would you not even worry about it? Decent, appropriate gear is kinda out of the question, but if that's the issue, good to know as well.

No biggie. Not really too concerned. Just seeing if anyone has any knowledge they'd like to share on the matter.

oh and I did try highpassing (with sonitus) for those earlier bass notes, but didn't do anything to the shape.

Cheers


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    Kev999
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    Re:Bass guitar modulating waveform/varying DC offset? 2012/04/21 03:42:25 (permalink)
    mattplaysguitar

    Take a quick look at this image of a bass track I just recorded:

    http://www.mattlyonsmusic.com/images/Bass_Waveform.jpg

    ...this 'variable DC offset' or whatever is going on in some of the notes may hit me a bit. Looking at it, you can see the positive part of the waveform is pretty flat and well compressed. The negative is almost uncompressed looking. There is a very distinctive trend going on here...

    No biggie. Not really too concerned. Just seeing if anyone has any knowledge they'd like to share on the matter.
    I recorded some bass samples and some of the waveforms looked like this too.  I presume that it is a low frequency modulation caused by a resonance in the wood.  It only happened on certain notes and only if I plucked the string very hard.

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    Jeff Evans
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    Re:Bass guitar modulating waveform/varying DC offset? 2012/04/21 03:54:53 (permalink)
    Matt you can get carried away with things like this. Many waveforms are simply not symmetrical and that is that. It does not mean there is any DC offset present at all. I have seen this before and done a DC offset check inside Adobe Audition only to find there is zero DC offset.

    I think you don't need to fix it because there is nothing to fix. Unless it sounds bad. Does it sound bad or faulty or incorrect? If it sounds good then it is good. As Danny has pointed out the only real time to do any DC offset checks is over a final mix.

    If you are really concerned send me the file over YouSendIt (or upload it to Soundcloud and make it downloadable) and I will check it for you for DC offset. I bet there is none.

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    The Maillard Reaction
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    Re:Bass guitar modulating waveform/varying DC offset? 2012/04/21 07:34:23 (permalink)



    That is not DC offset and the person who started this myth ought to be ashamed of how far it has spread.

    The non-symmetrical waveform is simply evidence or the result of having extra odd ordered harmonics on the signal and it likely caused by the distortion effect you have described using.

    If you like the sound you are good to go.

    You may also want to check if you have a DC offset... it's a totally different circumstance. You can run an analysis for DC offset and simply correct it. My guess is that if you find any DC offset it will be a very very small amount.


    very best regards,
    mike



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    Danny Danzi
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    Re:Bass guitar modulating waveform/varying DC offset? 2012/04/21 10:37:09 (permalink)
    Jeff Evans


    Matt you can get carried away with things like this. Many waveforms are simply not symmetrical and that is that. It does not mean there is any DC offset present at all. I have seen this before and done a DC offset check inside Adobe Audition only to find there is zero DC offset.

    I think you don't need to fix it because there is nothing to fix. Unless it sounds bad. Does it sound bad or faulty or incorrect? If it sounds good then it is good. As Danny has pointed out the only real time to do any DC offset checks is over a final mix.

    If you are really concerned send me the file over YouSendIt (or upload it to Soundcloud and make it downloadable) and I will check it for you for DC offset. I bet there is none.

    Totally agree with Jeff on this one, Matt. Don't let the look of a wave file or analyzer scare you or make you think you need to make changes based on what you see. I've seen some horrible looking "views" in my days...yet the stuff was either really good or made to sound really good with a few tweaks here and there.
     
    That said, there does appear to be transient peaks on each executed note. Most times you should be able to control those with the attack/threshold/ratio on your compressor. With peaks like what I'm seeing, it would be my guess you used a pick on this piece, yes? If so, you may want to make the compressor work a little harder to smooth them out a bit so the transient isn't as fierce IF it's as fierce as what the wave file looks.
     
    Also, Mike M is spot on with the DC offset thing. The guy that spread that rumor should be flogged with sub low frequencies until he yells "Uncle!" :) You can also enable Sonar to remove DC's while it records by enabling this option in your preferences. Even if you don't enable it, it's really hard to create enough DC to cause a problem unless you are working with synthetic sounds or sound effects etc. Even there, in order for a DC to play a serious role in screwing up your sound, it would have to be pretty intense.
     
    Most material that I master comes in with a DC of about .010%. Though that's not bad, you don't want to leave any in your final master and should take care of it at that point. Even with extreme limiting (that will make your DC go up) you're lucky if you'll hit .020%.
     
    I've never worried about DC offset and never heard a difference between a file that had it and one that had it completely removed. Now, I can SEE it because you can see the wave file change, but like I say, it's nothing to worry about. If I can be honest with you about it? I never paid much attention until I got into the mastering thing and studied the numbers part of it from Bob Ludwig. I figured if HE totally removes it on all his stuff, I better do the same. Bob Katz mastered one of my album and even he allowed a very slight DC to remain at .001%. If you can totally remove it at the mastering stage, go for it...but it's really nothing to worry about for the most part.
     
    Now, all of the above said...you're using that octave thing and this *could* cause a little more DC than you may want. So I'd definitely check out how much you do have at some point just to make sure there isn't some sort of anomaly making this bass a bit harder to control. Hope this helps...good luck man. Definitely take Jeff up on his offer if you need to...it's always good to get that second set of ears in there. :)
     
    -Danny

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    Guitarhacker
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    Re:Bass guitar modulating waveform/varying DC offset? 2012/04/21 16:49:38 (permalink)
     I too was concerned because I saw the same thing in my waves way back.....

    The important thing is the sound of the wave. If it sounds good, don't sweat what it looks like. 

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