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Ambient mic always causes phase issues with close mic on guitar cab

Discussion in 'Guitars' started by rectifryer, Jan 16, 2014.

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  1. rectifryer

    rectifryer Active Member

    I keep seeing recommendations on the net for using two mics on a guitar cab at once. One dynamic mic close to the speaker cab while an ambient room mic is 4-8 feet away. When I try this, I run into phasing issues as expected. I suspect there is no way around the phase issue aside from correcting it in the daw, perhaps that is the point?

    I am using an sm7b + m-audio solaris on a mesa cab.

    Edit for more relevant information:

    The ambient mic is about 6 ft from the cab, and 3 ft off the floor

    The sm7b is about 7 inches from the cone and 3 ft off the floor as the cab is raised to reduce reflections from the floor
     
  2. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    Slide the distant mic track to the left until the phase is minimized. Use your eyes to get it close then use your ears to make it right.
     
  3. rectifryer

    rectifryer Active Member

    So ambient mics are corrected in the daw in situations like mine?

    Just confirming.
     
  4. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    It's a valid technique. I've done it plenty of times. Whether it's the right thing to do is up to you and your ears.
     
  5. rectifryer

    rectifryer Active Member

    I am certainly not criticizing it; it's just tedious work thats all :D
     
  6. rectifryer

    rectifryer Active Member

    I am going to try out the MAutoAlign phase software and see if I can advance the ambient track versus delaying it. That way, I can just match the vst to the distance of the mic and not have to align every time I track.
     
  7. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    I didn't suggest delaying, I said to slide it to the left. It's brute simple to do, but whatever.
     
  8. audiokid

    audiokid Staff

    thumb
     
  9. audiokid

    audiokid Staff

    I had to look for a tutorial on this :




    This is fun :)

     
  10. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Another approach is to just move the mic around so it's not canceling as much. Lol the guy in the 2nd vid says "let me lower that cuz it's annoying". That made me smile.
     
  11. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    That just moves the cancellations around in the spectrum.
     
  12. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    It takes little more time to do it by hand, eye and ear, and you get to be in control of how it sounds.

    Could he have made it any more confusing? It doesn't help that he makes no distinction between phase and polarity.
     
  13. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Come on man, the whole idea of multi micing is an idea of fullness which means space. Space takes time and cancellation to develop when used w a close mic. Please take this as friendly disagreement but on a kit, it's mic'd up close too. Why is there a need to abnormally introduce phase things that aren't consistent w the original micing "assuming

    Jw. Isn't the phase relationships themselves creating the sense of dimension of space?

    naturally occoring oh/room mis are behind if you dare to look at them

    what is wrong w this? Electronic stuff aside, I'm silky taking about drum kits and the rest.

    i appreciate your thoughts.
     
  14. rectifryer

    rectifryer Active Member

    The sense of space isn't from comb filtering due to phasing effects between two mics. The sense of space comes from picking up the reverb(which does have its own comb filtering but is not the focus here) in the ambient mic.

    Thus, I advance the signal on the ambient mic with a phasing tool, no need to nudge it by hand every take but go ahead if you want to waste time IMO but maybe you have an easier daw to use than mine (reaper).
     
  15. DonnyThompson

    DonnyThompson Distinguished Member

    A few questions:

    Are you busing the two mics to 2 separate/discreet tracks, or are you combining both to one track?

    when you say "phase issues", are you talking about slight-to-noticeable actual and audible phasing ....or are you experiencing outright cancellation? You've obviously employed the 3:1 rule, so I can't see where you'd have cancellation issues.

    That being said, have you monitored the tracks in mono to listen for cancellation?

    And I'm just asking here, I mean no offense nor am I insinuating that you don't know what you are doing... but are you sure you're just not hearing the natural (and expected) tonal differences between the up-close mic and the ambient/room mic? You'll certainly have some delay between the 2 mics, because you've got one direct and one ambient mic, so it's natural for the ambient mic to have some delay in time as well as ambient reflection(s) from the room in relation to the direct/close mic...

    I guess what I'm asking is if this is a concern of what you are actually hearing? Or, is it more about what you are seeing on your track's waveform(s)?
     
  16. rectifryer

    rectifryer Active Member

    Polarity is a specification of phase.
     
  17. rectifryer

    rectifryer Active Member

    I would never employ, or attempt to employ, or care to pay attention to the 3:1 rule when ambient micing a single source. There is no ratio that is going to minimize comb filtering from phase effects. You can only shift nodes of cancellation as a function of multiples of the distance of the mics in relation to the speed of sound. That is not what the 3:1 ratio is for.

    Also, I went with the voxengo plugin. Sorry for the confusion. Thanks everyone for the help!
     
  18. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    And yet with a complex musical signal you can't treat them as the same or even interchangeable. On a practical level they are drastically different. You can't truly fix a phase problem with a polarity inversion. Any improvement is subjective, not objective. Of course with music the subjective is pretty important.
     
  19. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    I'm in total agreement with this. The 3:1 rule of thumb is for multiple sources.
     
  20. audiokid

    audiokid Staff

    lol, but the best part, he did say he isn't a sound engineer hehe No mention of checking mixes in mono either.

    So many mixes I hear have some to severe phase issues. I use my ears while moving or completely removing things until it sounds better. Drum tracks seem to be the worst.

    Transient smear.
     

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