How do mics become out of phase?

  • Thread starter Thread starter mrmeggs
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I'm not so sure!!!
I think I might have (Bi)Polarity issues!!!
 
UMM yeah. I see where you guys are going with this but I meant more from a practical point of view, thats what i mean when I say that I understand about phase and different waveforms hitting different mics etc. But I needed a practical description of how to deal with this 1. How do I determine that the wave form is out of phase, can you hear it directly? :D (say if I was micing a guitar amp with three mics or something (which one should be fixed?) and 2. how do I go about rectifying this problem. Sometimes you can understand how something works but it is harder to put this to practice with identifying it and fixing the problem properly. Thanks.
 
well, you should just be able to hear it. you'll hear a type of flanging sound and the sound won't be as full as it should be. If you have two or more mics on something, a good thing to do is switch the phase (or polarity or whatever the hell you want to call it) on that channel and see which sounds better. this may rectify the problem you're hearing, but it's also good to just move the mic around until you get rid of the phasing issue and get the sound you want.
 
So, if i have recorded a guitar amp that has mics out of phase (i should be able to hear it) it will drop in volume at certain points etc right? I understand that the wave form may be different at the point that it hits each microphoe and I am sort of understanding that if 1 mic is pointing down and the other is pointing up then the wave form will be upside down on one of them, right? Can I see this happen on my computer screen (I look at the waveform all of the time) what will it look like if it is out or completely the wrong way around cancelling each other out. I should obviously try to recognise this as I am micing up the amp, drums or whatever. Thanks Meggs
 
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well, it's hard to see in the wave form because unless they are exactly opposite eachother and the entire sound cancels out...only partial sections will cancel out. so maybe out of 10 seconds of a recorded part, maybe 1/3 of the wave form actually has phase problems...and zooming in to find these exact places is a bitch and a waste of your time. They make phase meters (plugins and hardware units) that can tell you if it's in phase or not. But I'd say use your ears.
IF IT SOUNDS BAD, FIX IT.


that's really all you should do.
 
mrmeggs said:
So, if i have recorded a guitar amp that has mics out of phase (i should be able to hear it) it will drop in volume at certain points etc right?
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Definitely you will hear it, especially if the two sounds are mixed at near equal volumes. The sound will comb-filter with some frequiencies cutting out and others adding in volume..
...if 1 mic is pointing down and the other is pointing up then the wave form will be upside down on one of them, right?
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Not at all. The variable is two or more distances (or sound time-paths of any kind) that are combining.
In general, when dealing with time related phase issues, the relative distance differences from the source determines which frequencies filter (add or subtract), and their relative volumes determine the depth of the filtering.
Here is a thread that might help. There's an amp-mic phase experiment in there too. :cool:
https://homerecording.com/bbs/showthread.php?t=139485
Wayne
 
Definitely get a Phase-Scope (if you don't already have one), use your ears first though. You're almost always going to experience phase issues in a mix. It's just a matter of how much is to much for the particular situation.
 
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