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Reverse phase before or after recording. Any difference?
Old 3rd June 2004
  #1
Gear Head
 

Reverse phase before or after recording. Any difference?

Is there any sonic difference between reversing mic phase after the recording?
If I find a track out of phase, does it matter if i just reverse it on the console? Or would you suggest re-positioning the mic?

Does it change the sound to do it one way or the other?

Thank you
blood
Old 3rd June 2004
  #2
member no 666
 
Fletcher's Avatar
Out of phase in relation what?

If you're talking about the polarity of the microphone, then yes, flipping the polarity prior to recording the sound does make a difference, in fact, flipping the polarity before the mic pre makes a difference.

No amplifier I have ever met [even Class "A" amplifiers] amplifies a wave form symmetrically and very few waveforms we record [especially the human voice] are symmetrical waves... so, if you run an asymmetrical wave form through an asymmetrical amplifier you're going to get different results from different polarity orientations.

Now, if you're talking about the phase relationship of two mics on a single source then moving the mic is indeed often the ticket to get the two sounds to sound better in mono... that or a variable all pass filter.
Old 3rd June 2004
  #3
LTA
Gear Addict
 
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Re: Reverse phase before or after recording. Any difference?

Quote:
Originally posted by bloodsweatfire
Does it change the sound to do it one way or the other?
It doesn't make a signifigant difference where you flip the polarity.

I've played around with absolute polarity a bit in the past. Honestly, i was just trying to figure out if the kick drum should have an initially positive waveform, or a negative one.

So, i recorded some minimally miced drums over some simple guitar + keyboard scratch tracks, and started flipping polarity. I started with the drums during playback. There was a difference, especially in the low end. I couldn't tell which was which, but i did prefer one over the other. This i found odd, working in the digital realm. So i started flipping polarity on the master output. Same change, although the other tracks where now slightly changing too.

Now, before i became completely frustrated with my DAW and equipment, i hooked up a speaker selector box so that i could switch phase of the speakers on the fly. If you want to try it, hook the positive lead from the speaker to the + on channel A, and the -/ground on channel B. Do the opposite with the negative speaker lead. Be careful not to short anything out, and if you're a/b box doesn't break then make the connection when selecting them, make sure you aren't playing back when you switch or you will momentarily short out your amp. Now, doing the a/b speaker phase thing, i was noticing an effect similar to switching the phase of the master output. I can't say this was exactly the same, but the change was similar. I just wasn't coordinated to turn a switch on a small box while click a mouse.

So, i would like to venture the conclusion that the speaker/air/ear assembly is far more asymetric than a class A amplifier, and that absolute polarity is very important, but where that state of being comes from doesn't really matter. I've never had a chance to delve into the world of preamp design, so Fletcher probably has more tuned-in ears in that department. I don't see why both can't be correct at the same time though.

Now, a better question is "what is the correct absolute phase?" Do i phase reverse the mic inside the kick drum, or the overheads over the drummer's head? Does swapping polarity on a guitar amp mic make a bigger difference than swapping polarity on a DI input? Will my car run cooler with a pusher or a puller electric auxillary fan?
Old 4th June 2004
  #4
Lives for gear
 
gear is cool's Avatar
Re: Re: Reverse phase before or after recording. Any difference?

Quote:
Originally posted by LTA


Now, a better question is "what is the correct absolute phase?" Do i phase reverse the mic inside the kick drum, or the overheads over the drummer's head?
this is a question that i've had also...
when i dial up a drum kit i get the o/h's in phase with each other
but the seem out with the rest of the kit
also where do you guys start when checking phase?
what is the base or anchor mics- kick and snare? o/h's?
phase on bass guitar trips me out as well
i run a di and mic the cab, when i flip the phase
it changes, not as much as with guitar or drum phase,
but i end up not flipping it
i have alot to learn about phase
i'm thinking of picking up the little labs phase tool
which i hear has a great di and splitter
m'man gil norton said i should get one...
anyone else use one of these?
sorry about all the questions and gratuitous name drop
joe
www.orbitaudiorocks.com
Old 4th June 2004
  #5
pan
Lives for gear
 
pan's Avatar
 

Absolute phase difference is most apparent at low frequencies and big transients. So start with the HiHat........errrr........KICK?!!!

n
Old 4th June 2004
  #6
There is only one
 
alphajerk's Avatar
 

dont forget the bass phase relationship to the kick as well.

i too have asked many times with no valid replies about the + vs - amplitude of the kick or rest of kit... i seem to think keeping the kick miced from the front and putting the rest 180 out works better, but it might just be mental.
Old 4th June 2004
  #7
Gear Head
 

Quote:
Originally posted by alphajerk
dont forget the bass phase relationship to the kick as well.

i too have asked many times with no valid replies about the + vs - amplitude of the kick or rest of kit... i seem to think keeping the kick miced from the front and putting the rest 180 out works better, but it might just be mental.
Hey AJ,
If the kick is mic'd out front, why would it be out of phase with the OH's or the tom / snare mics?
Knock all of them around 180?
It may be but I have been using this without any strange phasing issues that I can hear.
I have heard use of knocking the bass track out of phase to mix with the bass drum better but I have never had to that either.
Old 4th June 2004
  #8
LTA
Gear Addict
 
LTA's Avatar
 

Quote:
Originally posted by bloodsweatfire
Hey AJ,
If the kick is mic'd out front, why would it be out of phase with the OH's or the tom / snare mics?
Knock all of them around 180?
You are stumbling into the phase vs polarity problem. The 2 mics are in phase (the same time-distance from the source), but you need to look at the source of vibration. As a kick batter moves towards the kick mic creating a compression, the batter is also moving away from the drummer-side overhead resulting in a rarefaction. Overall, the diaphragms of the overhead and kick mic are moving in "equal" but opposite directions. Swapping the polarity of either mic will put them into relative polarity, so the electrical signals are moving in the same direction at the same time.

The only way to adjust phase is to alter the relative distances between the mics, or to add some sort of delay electronically/digitally.

Now, for absolute polarity, assuming properly wiring and speaker polarity, i prefer to base everything off the kick drum mic, so that the initial quarter-waveform of the low mode of the kick moves the speaker out towards the listener. I guess that would confirm the idea that the initial portion of a kick drum sound should be positive. Graph the function sin(x) from 0 to 2pi, with 0 being equivalent to the initial time of contact between the beater and the batter. I do actually think of phase in radians, and save degrees for angle measurements. If you want a graphic visualization of a polarity swap, graph (-1)sin(x) over the same period. For even more fun, graph sin(x)-sin(x), or sin(x)+sin(x+pi), keeping in mind these two equations may "look" the same but are not. I don't think you can graduate high school without taking trig, so you already should know this stuff. Remembering it is the trick.
Old 4th June 2004
  #9
Lives for gear
 
loudist's Avatar
 

Re: Re: Reverse phase before or after recording. Any difference?

Quote:
Originally posted by LTA
Will my car run cooler with a pusher or a puller electric auxillary fan?
From all I have read about this... a puller fan, especially if there are AC and transmission coolers involved.
They are only needed up to 30 mph or so, then the ram air effect takes over.
Old 4th June 2004
  #10
LTA
Gear Addict
 
LTA's Avatar
 

Re: Re: Re: Reverse phase before or after recording. Any difference?

Quote:
Originally posted by loudist
From all I have read about this... a puller fan, especially if there are AC and transmission coolers involved.
True. It's like pushing a rope. And in a roundabout way, a fan is a transducer. I wonder how many dB at zero Hz a 15 amp shop fan could spit out. If only the blades could be made infinitely light to eliminate the flywheel effect....

Now, a fan has a fairly laminar airflow going in as a result of the low pressure, but the high pressure output is turbulent and spills out. Nothing you haven't seen on the weather channel before.

Now, another question Is an airplane held up in the air more by the high pressure zone on the underside of the wing, or the low pressure zone above the wing? Does the ratio of high to low pressure alter when the plane is flying inverted?

Replace the wing with a baffle box, and airspeed with a moving speaker, and if i have a point to make, i've made it.
Old 5th June 2004
  #11
Lives for gear
 

Quote:
Originally posted by bloodsweatfire
Hey AJ,
If the kick is mic'd out front, why would it be out of phase with the OH's or the tom / snare mics?
Knock all of them around 180?
I follow a similar reasoning. The O/H's are a lot out time wise and only somewhat in polarity (0 Vs 90-120degrees?) albeit tilted toward the opposite if they are to the rear.
Wayne
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