Phase question

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newguy12
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Phase question

Post by newguy12 » Wed May 14, 2003 12:22 am

I know this is probably a stupid question but I'm new to all this. I read somewhere that if you are using two mics to record such as one on top of a snare and one below and they are out of phase, you can rewire one of the XLR cables to reverse the phase on one of them. Is this true and how exactly does one go about doing this.

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Re: Phase question

Post by penrithmatt » Wed May 14, 2003 6:44 am

well,one mic pointing at the head of the snare and another underneath pointing at the snares.....the two mics are facing each other,albeit through the drum,and are gonna be 180 degrees out of phase.if you have a phase reverse switch on your board/workstaion/whatever try flipping the bottom mic.the snare should now sound "more full".
as to rewiring cables,most gear is "pin 2 hot".by swapping pin 2 and pin 3 you "reverse"the phase of the cable.unscrew the barrel of the xlr.look at the three connections.you will see a number by each bucket.grab yer soldering iron and away you go
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helstab
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Re: Phase question

Post by helstab » Wed May 14, 2003 7:06 am

If you can't switch the phase on your board and your not running your parts into a computer how can you check for phase and fix it? besides recording somthing with 2 mics at 180 form each other how can I learn to spot when drums are going out of phase. Right now everything bleeds but I can't tell if it is out of phase or not. I think the snare might be because its hard to turn up when the overhead and snare mic are playing back with each other, but it doesn't sound bad. I think the frequecy that is out of phase is being cut by parametric eqing so it's not making anything sound really bad. But I don't how to check it.
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Re: Phase question

Post by helstab » Wed May 14, 2003 7:07 am

If you can't switch the phase on your board and your not running your parts into a computer how can you check for phase and fix it? besides recording something with 2 mics at 180 from each other how can I learn to spot when drums are going out of phase. Right now everything bleeds but I can't tell if it is out of phase or not. I think the snare might be because its hard to turn up when the overhead and snare mic are playing back with each other, but it doesn't sound bad. I think the frequency that is out of phase is being cut by parametric eqing so it's not making anything sound really bad. But I don't how to check it. does this make sense?
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Re: Phase question

Post by djimbe » Wed May 14, 2003 8:17 am

helstab, can you make a little polarity gender-mender out of a short length of cable and a couple of XLR's? Wire one XLR with pin 2 hot, and swap the hot lead on the other. Make sure you mark it as reversed polarity! Keep it handy when you set up mics so you can plug it in your signal chain to check what's going on. Finding such problems is easier when you test in mono out of a single monitor. Also, once you get an idea what it sounds like when you flip polarity, you'll find such problems easier. Like everything, practice is what helps you learn, so maybe make a point of doing a test setup on a drum kit with a couple mics and some kind of polarity switching cable that you move in and out of service. See what happens when you flip the top vs. bottom mic, or maybe you have one overhead that is badly interacting with the snare mic. Do the best mic setup you know how, then play with all the combinations of in phase/out of phase you can imagine. Yeah, plugging and unplugging things is a drag, as is adding extra connections to your signal chain, but when all else fails...
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Re: Phase question

Post by helstab » Wed May 14, 2003 8:43 am

Can I get some instruction on how to do this I would like to give it a try. The thing is I'm in limbo right now. I have recording on my mind 24/7 but I can't really do anything but ask questions becuase we are painting the new house and planing stuff so I wont have any time for the next 2 months. No time to read no time for anything. All I have is my free time at work, and luckily I have plenty of that.
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Re: Phase question

Post by xonlocust » Wed May 14, 2003 9:53 am

helstab-
i think djembe did a pretty good job of explaining the actual construction of the cable you need to build (if not - post to clarify what you didnt get).
one thing that helped greatly in understanding phase issues for me is learning to hear what's out of phase vs in. soundguy dave posted something a while back which was great advice (paraphrasing here).

start simple and plug in 2 mics. put them both right next to each other pointing at you or whatever source. then keeping one in the same place, slowly sweep the other in an arc and while you're doing this, listen in headphones, and hear how the sound starts to hollow out in places. that's out of phase. you can try this with a snare drum too to hear it in more of a real context.

another thing that helps is if you visualize the physics of what's going on when you're setting up your mics. in your mind, slow down the soundwave vibrations real slow and imagine some animation showing how the sound is traveling. for drums, think about one side being the beater side and the others being the resonant. in most cases, your close miced snare and toms come OFF the top, contrast that to your ambient mics which are kind of coming off the bottom instead of top. or your kick, is micing off the bottom kind of (on the oppisite side where the beater/stick hits).

now, again - that's all kind of "in theory" stuff, and is just a starting point. bottom line is you've gotta use your ears and if it sounds good, put it to tape. but at least it's something to think about. you're inevitably going to have some phase issues no matter what you do setting up more than 1 mic on a single source, but minimizing them to an acceptable level is about all you can do.

hope that helps - and others please add on or clarify if i've missed any points or have my head in my ass somewhere in there.

nick

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Re: Phase question

Post by jb5dogs » Wed May 14, 2003 9:56 am

a simplistic example...

if you're recording one source with two mics, pan both hard either direction, and hit the mono button on your master. if the result is lifeless as compared to the stereo, then you probably have some phase issues.

getting in-phase is not an either/or proposition, but a spectrum, so you may be in-phase, 180 degrees (exactly) out of phase, or anywhere in-between. many people measure the distance from 2 mics to the loudest sound source (the snare in a drum kit), and make sure both mics are equidistant, which should assure that they are more or less in phase.

all of the above is complicated by using more than 2 mics, and recording instruments whose sound is not emitted from a single point.

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Re: Phase question

Post by helstab » Wed May 14, 2003 10:08 am

I have never made a cable before. I guess I'm being lazy sorry, but I was just asking for text explaining what it is exactly that I will be doing. I am a newbie and not afriad of it so please excuse me if I don't make sense some times. I just read bits and pieces about everything which is leaving me with no general understanding of how some things work. If I'm going to make a cable or alter one untill I know exactly what it is that I'm doing. Don't talk down anything though I will figure it out and thanks for your help as always.

I think its coming down to going back to school to take some classes on electronics if I really want to understand.
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Re: Phase question

Post by soundguy » Wed May 14, 2003 10:23 am

matt-

your XLR is wired-

Male Female
pin1 pin 1
pin2 pin2
pin3 pin 3

your phase cable, which you will brightly labe as such is wired:

Male Female
pin1 pin1
pin2 pin3
pin3 pin2


in order to fix phase, you need to understand the comb filtering sound. Take two mics, point them at each other and listen. move one around. the is the comb filtering sound that occurs where your mics are picking up the same sounds at a different phase of their cycle and they are canceling. To fix, you just move the one mic until the sound goes away. dealing with this on drums can be tricky, make sure to monitor your drums in mono when you are setting up your mics, but if you are using lots of close mics and are in a reflective space, there is always gonna be something that is thinning out the track, its not really something that is very easy to get %100, but %96 usually will do ya fine...

dave

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Re: Phase question

Post by helstab » Wed May 14, 2003 10:46 am

Thank you. I'm defiantly going to play with two mics as you suggested as soon as I can. I would still like some text explaining the "science" of what is happening. I understand what phase is and can picture it, but I like to read.
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Re: Phase question

Post by xonlocust » Wed May 14, 2003 12:17 pm

matt-
here's a link that should help:

http://www.physics.umd.edu/courses/Phys ... ch17ab.pdf

read through it all to get a good understanding of the physics of sound waves, but once you understand the basics of a simple sine wave, the phase stuff we're talking about here comes into play in sections 17-8 and 17-9 etc. alternatively, you can just get pretty much any physics book from the library and it'll be bound to have something for you.

here's a link that may help for your connection

http://www.clarkwc.com/PinOutXLRBalanced.htm

if you think minutely again about your mic cable, it's really 3 small cables joined in 1, and all you're doing is flipping 2 of them intentionally to make your polarity jumper cable. each pin is connected to a different wire in your cable. i hope that makes sense! what this does, if you make an analogy to the physics book chapeter link above, is think that wherever the top of your wave is - after plugging in this cable (or pressing your polarity flip button on your console) is taking where it reads +10 (an arbitrary number) and make it flippes to -10 instead- and inverting your wave.

hope that makes sense.

there are a lot of resources on this stuff even at the library, that aren't "recording" specific - but physics is physics and that is one thing that hasnt changed in like, ever. so, you can pick up some book from the 60s that looks stupid and everything is still 100% applicable to you now.

hell, i even took an oceanography class back in college and that covers the exact same stuff. shorelines are like walls. storms go in and out of phase - tidal waves are like resonant frequencies off the world.

hope the helps!
-nick

-nick

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Re: Phase question

Post by newguy12 » Wed May 14, 2003 1:48 pm

I was just curious, if I didn't have a phase reverse switch on my mixer or mic pre and I didn't want to wire up an XLR cable to reverse the phase would it be feesible to use a direct box that has a phase reversal switch on it. For instances, I have a behringer (its the one with 4 channels of DI) DI with a phase reverse switch on each channel. Could I plug a mic into my mic pre, run the output into the behringer DI box, flip the phase reverse switch to reverse the phase and then run that into my recorder?

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Re: Phase question

Post by jb5dogs » Wed May 14, 2003 2:45 pm

http://1staudiousa.com/spcint.html

middle of the page

phase reverse adapter ($12)

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Re: Phase question

Post by soundguy » Wed May 14, 2003 2:50 pm

if the DI has a line in, it might work, most DI's are expecting an instrument level though. Try and see.

If you dont want a cable, you can also build a simple box.

Get a hammond box and a male and female panel mount XLR.
Get a good DPDT switch. A good one.

mount the switch and XLR's on the box.

wire the pin 1's together on the male and female.

the DPDT will have six terminals:

X (a) X (b)

X (c) X (d)

X (e) X (f)


Wire the XLR's to the switch lilke this:

female
pin2 - C
pin3- D

Male
pin 2- E
pin3- F

pin 1 should be connected from one connector to the other bypassing the switch.

On the switch itself, install two jumpers.

JUMP
a to f
b to e

In one position, the signal goes straight through the switch, in the other, the polarity gets switched. You can build a few channels of this depending on how big your hammond box is, and the nice thing is, you'll never mix up a mislabeled phase cable. And there are no electronics involved, totally passive. Another easy utility project that will constantly be of aid if you dont have phase flip switches on your console or outboard mic pre's/eq's.

dave

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