Eliminating "phase" problems with the "phase reversal" switch

shackrock

New member
alright......Now how about this:
Can anyone give me a procedure on how to ELIMINATE PHASING (if i'm using 2 mics).

How do i use this phase reversal switch to do so? I really don't know how i would go about doing anything like that...haha

however, here would be my set-up:
-close miced distorted guitar with SM57
-maybe 6 feet back, wherever it sounds best, miced with either mxl 603s or mxl v63m

thanks
 
Phase issues are not usually a problem if you're close-mic'ing an amp and using a room mic for ambience, unless it's a really bad (small and very reflective) room.

The 3:1 rule means multiple mics should be placed at least 3 times the distant apart as they are from the source (and you're following that rule by having the room mic 6 ft or more away). Are you sure you have a polarity problem as opposed to bad mic or poor choice of placement? Also, is the room mic close to wall? (you may be getting reflections from the wall interfering with the direct sound hitting the room mic.

In any case, you should be able to find a room mic position that works for you without you having to flip polarity on the mic pre....
 
heres an edited reprint:

Make DAMN sure your guitar is in tune, and intonated properly. Different intonations and even VERY slightly different, can make whole separate flavors of distortion so get it as close as you can. If you know the difference in distortion sound between a 24 3/4" scale guitar neck and a 25 1/2" one then you know what Im saying.

Now on to your preamp, or preamp section of your head, depending on what you got. In most cases, metal guitar tones come from a LOT, a WHOLE LOT less ( thats right LESS ) distortion/preamp gain than you would use live. For riffs and chord changes, the REAL heaviness comes from dynamics, the fact that it gets LOUDER when your pic hits the string than when the string is just resonating.
It seems obvious but its not really. You need to MAXIMIZE the dynamic range at this stage because from here on out, the signal is going to be compressed and degraded in all sorts of ways. In most cases the gain should be about where, when if you SOFTLY strum a chord it actually comes out clean. Transistor amps/pedals may not do this ( some will ) which is another reason tubes are usually perferred for this type of thing.
Now, tone. Scooped mids, cranked bass and treble right? WRONG. For recording you will need a LOT more mids than you normally would for live. You need to be heard. The way our ears work, we take most of our cues from the midrange. Get as much body in the tone as you can....not bottom, body. You can always scoop it out later if you must. Like the lumberjack says " always cut long" right ?

Ok, on to the power amp or the power section of your head if you use one. Here is where you start the dynamic reduction process. You want to get a sound with enough sustain to work, but being careful whether or not you want to HEAR power tube saturation or speaker distortion. In some cases you want to, in some cases you dont. Get a good sound that you ENJOY. Make sure ( if you can at this point in the recording) that it fits with the other tracks. You will probably use a speaker that you wouldnt like live for this process. A speaker with more mid's than normal, like a celestion Vintage 30 or maybe a Kendrick. Greenbacks are good live, but sometimes lose that all important midrange on tape. Watch the speaker distortion, get a power level that makes COMFORTABLE dynamics for you. Errr on the LESS compressed side so you gotta work just a WEE bit harder than normal to crunch it up.

Now, stand in the room with the amp. Get your head moving around until you find the one speaker that sounds better than the others, or maybe just a real good spot where it seems to sound best. I am assuming we are NOT going after a " room " sound at this point. Stick a 57 RIGHT there, where your ear was.
Now, at the console, FIRST verify that that is *roughly* the sound you heard out there. Be sure levels are where they should be etc...no eq at this point on the console. Have someone move the mic back towards or away from the cab ( or do it yourself with headphones ). You are doing two things with this:

1) changing the ratio of direct( from the speaker ) vs. reflected ( yeah you might be only a few inches from the cab but the room still is playing a HUGE part) sound coming into the mic

2)changing the amount of dynamic compression that the actual volume of the speaker is causing in the mic's diaphragm, ribbon or voice coil. You are changing the BEHAVIOUR of the sound here.

Once you like the placement of your mic, its time to get REAL tricky.

ONE mic is almost never enough, but with two or more, PHASE CANCELLATION rears its ugly head. But we got a trick for that right?

Here comes

Put the guitar down. Make it make noise, or take the cable off and stick it on something that will make noise. This noise has to be stable and constant....a fender strat's hum is perfect for this assuming it has some midrange harmonics to it.

Using your console's meters, bring that noise up to wherever your "zero" is. This will probably require a LOT of mic pre gain so make sure your speakers are turned down. DONT let anyone touch the guitar or whatever the noise source is. Once youve got the signal to zero, mute the channel

Next go into the room with the amp, and put another mic about equidistant from the speaker as the first mic is...Be careful not to disturb Mic #1.

Back in the control room, bring Mic #2 up to zero

Now, VERY IMPORTANTLY, pull Mic#2's fader ( NOT mic pre ) down to -infinity. Unmute Mic#1. Slowly push Mic#2's fader up towards zero.

If the volume at your final LeftRight Mix buss on your console goes UP, you need to flip the phase of mic #2. If your console doesnt have a phase switch, make an out of phase cable. Just reverse pins 2 and 3 on an XLR, and make DAMN sure you label that cable from now on so you dont screw up some overheads or something.
Remember if the volume goes UP flip the phase

If the volume goes down we can proceed...keep flipping the phase until the volume goes DOWN when they are at their zeros.

Now pick up a bat, knife or gun. Whatever you are best with. Threaten anyone in the control room with it and say " DO NOT touch that guitar !!!! I am gonna have headphones on at extreme gain levels and am risking it all so you can have a good guitar sound ". Wave the weapon around menacingly until you are SURE that they get the point. Kick them out and lock the door if you cant trust em...now is NOT the time for gags.

now go out to the amp with headphones on. You will hear a hiss or buzz or hum...make sure the hum in the phones is louder than the one you can hear directly from the amp.

DO NOT cough, you will blow your eardrums right into each other. Becareful of any noise that may be present.

Now, EXTREMELY carefully, move Mic#2 back and forth, left and right. SLOWLY

You should hear a whoosh, much like a flanger pedal would make.

The trick here is to find the spot where the LEAST noise is coming out of the headphones. Keep moving the mic you will find it.

have you caught the theory yet? We are looking for the spot where the two mics are THE MOST in phase with each other. If one is phase flipped, then at the most in phase spot, they will nearly cancel each other out. FIND THAT SPOT

once you got it, take off the phones and go back to the console.

Turn both mic preamps gains ALL the way down. Put fader one at the unity position on your console. Play your guitar and turn up the mic pre gain until you hit zero. Now mute Mic #1. Now turn fader 2 to the unity position. Bring up Mic pre #2 until you hit zero.

edit : OOPS!!!!!!
I forgot, tho you prolly figured it out. Unflip the phase on mic #2 at this point so that both mics are IN phase. Sorry about that

Unmute #1 and mess with the faders. Those two faders now become the BEST EQ money can buy! Turn up one then the other, experiment to your heart's content. Once you got a sound you like, buss them together and send em to a track...or keep em separate if you want some choices later...

revel in your glorious new tone!

once you got it down you can experiment with making the distances between the mics greater, and or/sending different tones thru the amp for emphasizing different frequencies.
At greater distances the phase cancellation wont be as complete, but you will by now have an idea of what it should sound like when they are close to 100 % out of phase

Aaron Carey
StudioZ/Pipelineaudio
www.studiozpro.com
 
As Bruce said...

The 3:1 rule is something you should have in mind, just in case, assuming that you are doing a single mono guitar track (or panning both to the center). If you are willing to do a hard left & right pan of those mics, that would be a stereo guitar track and 3:1 will NOT apply in that case, since you will not have phase cancellation.

Now, phase inversion is necessary when, for example, you use one mic in front of the amp and other in the rear part (open back) at about the same distance from the speaker cone. Those mics will have a phase problem, since the front one is getting a positive signal and at same exact moment the rear one is getting a negative signal. So, of course if you put them together, you get cancellation. Now, if you reverse the one on the back, it will be getting a positive signal exactly like the one placed at front.


Peace...

PC
 
Re: As Bruce said...

PowerCouple said:
Now, phase inversion is necessary when, for example, you use one mic in front of the ...



It is NOT PHASE inversion. It is polarity inversion. Using inaccurate terminology when discussing this subject leads to confusion in the minds of those who are inexperienced. I am sure you understand the difference, Power, but the original poster, and many others who either will (or should) read this thread do not. Phase and polarity are NOT the same thing, and the subject is important enough to deserve care when talking about it. If you don't understand what I am talking about, read the link in my post above, and follow the links in that thread.

Light

"Cowards can never be moral."
M.K. Gandhi
 
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