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Strange Wave Form

Discussion in 'Recording' started by ClarkJaman, Jul 14, 2012.

  1. ClarkJaman

    ClarkJaman Active Member

    Hey Guys!

    Screen Shot 2012-07-14 at 12.56.24 PM.jpg

    This is an acoustic guitar recorded line in with the built in pickup. Why do the transients point upwards but not really down? It's not using the whole space. What does this mean?
     
  2. hueseph

    hueseph Well-Known Member

    Someone will answer you. Just be patient. I don't know the answer to this. It may be a phase thing. It may be a view setting in Cubase. I don't know. I'm sure someone here will though. Boswell or dvdhawk. Some of these guys are very knowledgeable. I wish I could count myself among them but they are leagues beyond my ability.
     
  3. ClarkJaman

    ClarkJaman Active Member

    Don't worry, I am patient. :)
     
  4. Laurend

    Laurend Active Member

    Recording an acoustic guitar output on a line input isn't satisfying from a technical point of view. A high impedance input (DI) would provide much better results.
    The wave form is pointless. "Is you're sound OK?" is the only serious question.
     
  5. ClarkJaman

    ClarkJaman Active Member

    I can't remember for sure, but I think I was using a DI box. This isn't about the quality though. I was just recording a scratch/guide track while I was tracking drums with a client. I am just curious what this means. And no, the sound was terrible, lol.
     
  6. DrGonz

    DrGonz Active Member

    Take the track as an independent track in some editor (soundforge, wavelab or whatever...) and apply DC offset correction. What does the wave form look like after you run DC offset correction?
     
  7. thatjeffguy

    thatjeffguy Active Member

    Ditto DrGonz's suggestion... looks like a DC offset issue. Most DAWs provide a "correct DC offset" function for this.

    Jeff
     
  8. ClarkJaman

    ClarkJaman Active Member

    I don't think it's a DC offset issue, because the wavefoarm is still centred on the 0dB mark. It just extends further up than down. I tried removing DC offset on my DAW and it didn't make a difference. :/
     
  9. Laurend

    Laurend Active Member

    It seems that the positive part of signal is more amplified than the other.
    Does your guitar needs two batteries to power its preamp? A weak amplification related to an almost empty battery may explain this poor sound.
     
  10. Boswell

    Boswell Moderator Distinguished Member

    One answer to the original question is that waveforms can look like that - it's not your eyes that respond to the sound. I'm assuming that the recorded sound is OK, and that you are tracking this down out of interest and not trying to diagnose a sonic problem.

    Is this recorded from a magnetic pickup on the guitar rather than an internal guitar mic or an acoustic pickup? A magnetic pickup is a velocity transducer and captures a representation of the speed at which the string is moving and not the position of the string. Guitar strings move rapidly on the first release after the pick hits and then, depending on the players hand action, can damp relatively quickly, unless they are open (unstopped).

    The first check here is to see what happens to the waveform on an up-pick rather than a down-pick. If the higher peaks of the waveform are now in the negative half, then there is the simple answer. If the waveform still looks similar, then make sure you are going directly from the guitar pickup into a pre-amp DI input and not through a pedal or some other effect unit. If the waveform still looks the same with a clean chain from pickup to DI, check that you do not have any compression or other amplitude-altering effect set in your DAW.
     
  11. ClarkJaman

    ClarkJaman Active Member

    Thanks for stopping by Boswell. :)

    You are completely right, I am tracking this down out of interest... No pun intended. ;)

    The pickup was not magnetic, but now I am having the same problem except negative instead of positive with my bass guitar, which is of course a magnetic pickup. Check out this screenshot:
    Screen Shot 2012-07-16 at 7.48.49 PM.jpg

    I am missing headroom because of this, right? That is the real problem that I am trying to solve here. I could have a louder signal if the signal was going as far positive as negative. And if I run a compressor on this, it will compress the positive and negative waves, right? That's no good. This screenshot was recorded going into a DI box with the filter turned on (I don't actually know what the filter does, but it must be good, right? Lol). I tried the up-picking and down-picking thing, but it doesn't seem to make a difference. And I am pretty sure I don't have any compression or effects on the way in on my DAW that could effect the recorded wave form. :/
     
  12. BobRogers

    BobRogers Well-Known Member

    I don't have any better explanation than Boswell, but I do want to comment on your "I'm missing headroom because of this," "I'm not filling the whole space." This is bad mindset to have for digital recording. It makes sense if you are recording to analog tape (with a tiny signal to noise ratio compared to digital and a musical way of dealing with clipping), but not to 24bits of digital media (with huge signal to noise ratio and harsh clipping.) I try to maintain a consistent level of RMS (average) level on all of my tracks. That means that if my drums are tracking at -6 dBFS peak, then bass (which has 6-10 dB smaller dynamic range) should track with peaks at something like -12 dBFS peak level. One of the biggest beginner mistakes in digital recording is tracking too loud. You may not clip on the original track, but you will clip in the plugin or clip in the mix.
     
  13. ClarkJaman

    ClarkJaman Active Member

    Wow, that's definitely a mistake I am making then, and I'm glad you pointed it out. I thought you should always record as loud as possible to get as much dynamic range as possible. I always try to aim for as loud as possible without peaking.

    How do you measure the dBFS level? I know that half way between peak and silence in -6dBFS, but that's the only reference point I have.
     
  14. ClarkJaman

    ClarkJaman Active Member

    I found another spot, this one is worse than all the rest. This is the same acoustic guitar as the first screenshot, tracking much higher positively than negatively as usual, but in one spot it peaks negatively out of nowhere.

    Screen Shot 2012-07-17 at 10.49.52 AM.jpg


    Now I know for sure that this would kill the headroom. :/
     

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