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What is phase?
Old 8th July 2005
  #31
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mtstudios@charter's Avatar
 

Common Mistake

Just use your ears, flip phase with snare and ovrhds, if it sounds fatter then you got it right, if not, don't. It isn't always the same. Some engineers just don't check it.
You don't need to know the pin configuration, unless somebody is looking for an explanation to why it sounds better or worse.

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Old 9th July 2005
  #32
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Old 9th July 2005
  #33
Quote:
Originally Posted by tbrault
I'm not an expert either, but I think I can help. The simplest way to think of it is this:

Phase is in reference to time. Any phase difference can be correlated to a time difference for a given frequency. ITD, or Interaural Time Difference, is the way that humans detect direction above about 1kHz, and is essentially dependent upon the 'phase shift' introduced by sound hitting one ear before the other. Phase shifts can take place in either acoustic or electronic environments.

Polarity is MUCH simpler than phase. A poliarty shift mirrors the signal and essentially makes what was positive into a negative, and vice-versa. In math terms (skip this if its not your thing ) you multiply the function by -1, or flip it about the X axis. A +.5 volt charge would be made into a -.5volt charge. It is an electronic function stike .

For another explanation: If you think of a mic capsule being pushed in and out by the compressions and rarefactions of a sound wave, poliarty is essentially (and forgive me for possibly over-simplifying this) whether a 'push' on the capsule causes a positive or negative voltage change to the signal.

To sum it up: Phase is dependent upon time, Polarity merely 'flips' the signal upside down.


I hope that helps, and please correct me if I've mispoken.
cool, thanks, sound is such a complex phenomenon isn't it ?
Old 9th July 2005
  #34
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Larrchild's Avatar
 

"cool, thanks, sound is such a complex phenomenon isn't it ?"

Complex is about the best word you could use.

For those with many drum mics, for instance. Imagine the interaction of 6 or 8 drums going into say 10 mics. It's a phase free-for-all. All those drums arriving into all those mics at slightly different intervals makes Andy Johns look like a genius for using 3 mics. I guess we could use electronic toggle switches to turn them on during the beat. But that went out with the Mullet. With a lot of messing around, you can get things tamed in phase-land.

I'ts very complex, tho.
Old 9th July 2005
  #35
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Curve Dominant's Avatar
Quote:
Originally Posted by Gideon
No, phase is a real constant in an imaginary exponential:

z=exp(wt + iø), ø real, ø=phase.

Half life is the value of T such that exp(-kT)=1/2 i.e T=ln2/k where k is real.
Thanks for putting a finer point on it, however, I find it more useful and more easily understandable for the non-scientist audio engineer to picture phase in parts dissected by the zero crossing, since that's what most of us see on the DAW graph these days.

No biggie. Half-life, whole-life; tomato, to-mah-toh. But let's not call the whole thing off, because...

One issue which seems to get ignored or overlooked is this: Phase anomolies are naturally occurring features in sound and music. We hear them everywhere. All you have to do is turn your head a little bit when listening to something, and you will hear phase shifting.

One can easily end up on a goose-chasing excercise hunting down phase anomolies, and end up ironing out all sorts of interesting character from a recording.

YMMV.
Old 9th July 2005
  #36
Gear Head
 

Thumbs up

Quote:
Originally Posted by Mario-C.
cool, thanks
never a problem, thats what we're all here for!
Old 9th July 2005
  #37
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Is this a cause of being out of Phase?

I notice alot when I am working with synths and especially soft-synths, that when I audition my mix in mono, the keyboards just dissappear. I find this alot when working with soft-synths like Vanguard etc ... the synth patch sounds great in stereo, but when I switch my mixer into mono mode, the synth patch basically dissappears. Any fast way to fix this in protools? Is there a phase correcting pluggin?

Regards,
ian
Old 9th July 2005
  #38
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I think I found the answer

Man, I knew there was a reason software comes with a manual ... the Digirack eq's in PT easily flip the phase of a channel. It seems to have fixed my synth recording problem nicely

So, with a PAZ meter on the track, I noticed that there was alot of 'anti phase'. So, I am assuming that is bad. I put a Digirack EQ on the same track and then hit the phase button on one of the channels, go back to PAZ meter, and the 'anit phase' stuff is gone. And the sound is fuller as well, not as thin sounding.

I am not experienced at all when it comes to recording stuff. So my final question would be, do you experienced guys check phasing on each track usually when mixing? Is phasing best heard when listening to a mix in mono and if certain sounds dissappear, it means there is a phasing problem?

thanks,
Ian
Old 10th July 2005
  #39
Gear Nut
 

Phase cancellation makes for great eq!
Old 12th July 2005
  #40
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Besides flipping the polarity, what can you do to line up phase relationships better? I'm thinking of getting an IBP. I always have a problem when I record guitars with mulitple mics, drums too, but especially the guitars suffer the most from poor phase issues. How do you guys work around this problem? Michael Wagener's technique with the pink noise and headphones sounds interesting... his tones are the ****. What else can you do?
Old 12th July 2005
  #41
Gear Guru
 
lucey's Avatar
Quote:
Originally Posted by arrogantbastard
What else can you do?
move mics, less mics

IBP ... I have 4 just in case




for guitars try a ribbon and an omni ... with the omni directly over, or under the ribbon, and blend in the room verb to taste

cardioids have inherent phase issues, multiplied when used together.
Old 12th July 2005
  #42
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Please exuse my ignorance here, but should polarity always start on the upswing into the positive area above the zero crossing? I've noticed that when I'm editing tracks some start up, some start down, and some its hard to tell because there is no big transient to start off with.
Old 12th July 2005
  #43
Gear Head
 

Smile

Quote:
Originally Posted by git345
Please exuse my ignorance here, but should polarity always start on the upswing into the positive area above the zero crossing? I've noticed that when I'm editing tracks some start up, some start down, and some its hard to tell because there is no big transient to start off with.

Positive polarity makes your speaker cones move towards you, and negative away. When your kick drum hits, would you rather it push air at you or pull it from you?
Old 12th July 2005
  #44
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toolskid's Avatar
 

Quote:
Originally Posted by tbrault
Positive polarity makes your speaker cones move towards you, and negative away. When your kick drum hits, would you rather it push air at you or pull it from you?
well... I've been told my kick drum sounds both 'blow' and 'suck', maybe its not a polarity issue in my case...
Old 21st July 2005
  #45
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chrisrulesmore's Avatar
Phase issues with multiple mono tracks!!!

if you recorded everything in mono, one track at a time, A+ phase. if you record looped stereo drums, and mono track everything else, A+ phase.

In reference to the quote above, I am noticing that when double tracking two separate mono guitar tracks using the exact same mic and placement and panning hard left and right, everything sounds great on playback. However, as I pan inward I start to hear an awful shrinking of the sound and some horrible phase cancellation. I thought if you recorded each track separately, you would have no phase problems? What am I screwing up here? BTW...drums are looped stereo!
Old 21st July 2005
  #46
Gear Guru
 
lucey's Avatar
Quote:
Originally Posted by chrisrulesmore
if you recorded everything in mono, one track at a time, A+ phase. if you record looped stereo drums, and mono track everything else, A+ phase.

In reference to the quote above, I am noticing that when double tracking two separate mono guitar tracks using the exact same mic and placement and panning hard left and right, everything sounds great on playback. However, as I pan inward I start to hear an awful shrinking of the sound and some horrible phase cancellation. I thought if you recorded each track separately, you would have no phase problems? What am I screwing up here? BTW...drums are looped stereo!
well, i was oversimplifying ... sorry.

if you're double tracking gtrs (especially using all the same gear, gtr, amp, mic, pre, etc) then you could be close enough on the second track to have things get ... um, interesting.

phase of a wave is the place in time of the various frequencies, so you can have phase cancellations all across the spectrum.

if you're double tracks are very close in time (which goes back to performace and the gear combined) you could hear a lot of weirdness as the get on top of each other.

not sure if this is good for this song (and mixers with years of experience may have a better solution) but if i was faced with that i might hard pan the guitars for a chorus and use a 3rd track by itself, set back a bit, for a verse.

or get an IBP and tweak on of them a few degrees on the low (if it works) or more likely the high setting of the IBP.
Old 21st July 2005
  #47
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Seamus TM's Avatar
 

Well, when kids are acting strange and doing things that they normally wouldn't do they are "in a phase."

Seamus
Old 29th August 2012
  #48
Jye
Gear Head
I thought it might be best to continue on this post rather than start a new one...

My kick mic seems to be about 90 degrees out of phase with my overheads. Didn't know much about phase at the time of tracking.

Is there a way to affect phase 90 degrees? Should I just move the kick mic regions so they are in phase? Is there anything I can do?
Old 29th August 2012
  #49
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You can buy software or hardware that can be used to tweak phase alignment. Little Labs sells the IBP (In-Between Phase) unit and UA sells an IBP plugin for UAD-2. But it's worth your time to tweak mic positions, move instruments within the room, etc., before a device like the IBP, in my opinion.

How did you determine your 90 degree out of phase estimate?
Old 29th August 2012
  #50
Gear Maniac
 

OK, seriously though, what IS phase??
Old 29th August 2012
  #51
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Quote:
Originally Posted by mindkontrolle View Post
OK, seriously though, what IS phase??
That's what my kids are going through.
Old 29th August 2012
  #52
Jye
Gear Head
Quote:
Originally Posted by Syncamorea View Post
You can buy software or hardware that can be used to tweak phase alignment. Little Labs sells the IBP (In-Between Phase) unit and UA sells an IBP plugin for UAD-2. But it's worth your time to tweak mic positions, move instruments within the room, etc., before a device like the IBP, in my opinion.

How did you determine your 90 degree out of phase estimate?
I noticed the sine waves on the two OH mics are very close in their look at the start of a transient, ie their waves both go up and down, almost in unison, at the start point.

When the 2 OH mics waves are beginning to go up on a kick drum note, the kick mic is halfway through the 'up' movement of its waveform. That and I don't think it is sounding right both when polarity is untouched and switched. I hope I am checking it right...
Old 29th August 2012
  #53
Gear Maniac
 

That's just time alignment issue. Your kick drum mic hears the signal a few milliseconds before the overheads do. It's a simple function of speed of sound and distance.
Simple way to fix it is to slip your overheads forward in time (to the left on your DAW), so that the waves peak at the same time. That will bring the overall sound of the kit more in focus. Then high pass your overheads so that you don't have LF build up on the drum mix.
You can bring all drum mics in focus this way by slipping every track so that it aligns with the snare. Just look at the bleed from the snare in all other mics and slip them so that they peak at the same sample. If you do this for the room mic you will lose some of the natural ambiance. But overall sound of the kit will get a bit larger at the cost of sounding less natural.
Old 29th August 2012
  #54
Quote:
Originally Posted by Thuneau View Post
That's just time alignment issue.
That's what phase *is*. A time alignment issue.

Quote:
Originally Posted by Jye View Post
When the 2 OH mics waves are beginning to go up on a kick drum note, the kick mic is halfway through the 'up' movement of its waveform.
Not to be too nitpicky, but what you are describing is 45 degrees out of phase. It would be 90 degrees out of phase if the kick track had reached the peak of its waveform when the OH tracks were just beginning to rise.

The tracks would be 180 degrees out of phase if the OH waveform had reached the zero crossing and was starting to descend when the OH waveform was at the zero crossing but was starting to rise. The tracks would be 270 degrees out of phase if the kick had reached the bottom of its downward cycle when the OH were just starting to rise, and the tracks would be 360 degrees out of phase if........ oh wait, nevermind. heh
Old 29th August 2012
  #55
Jye
Gear Head
Thanks for the explanation, Thuneau. I'll have a play with moving tracks in time. I dunno, I thought screwing around with tracks time in relation to others was a no no, and might start a rapture or something. Seems time-aligning the tracks like this would be beneficial for getting a 'modern' sound with the big (or in-your-face) vs natural sound tradeoff you describe.

mindkontrolle, I believe there is plenty of literature on phase with links posted earlier in this thread, and google searches will probably yield something.

squirrel, a poor explanation on my behalf, but yes the kick mic wave was at the peak of its 'above 0' journey
Old 29th August 2012
  #56
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Quote:
Originally Posted by chrisrulesmore View Post
if you recorded everything in mono, one track at a time, A+ phase. if you record looped stereo drums, and mono track everything else, A+ phase.

In reference to the quote above, I am noticing that when double tracking two separate mono guitar tracks using the exact same mic and placement and panning hard left and right, everything sounds great on playback. However, as I pan inward I start to hear an awful shrinking of the sound and some horrible phase cancellation. I thought if you recorded each track separately, you would have no phase problems? What am I screwing up here? BTW...drums are looped stereo!
I'm a little confused on your first paragraph.

Generally you're gonna be fine phase-wise if you're recording two tracks separately, but there's no magic there. If you've got a player with a knack for playin' it exactly the same way twice, you can still run into phase problems. This tends to happen on certain instruments more than others, and distorted electric guitar can be a culprit. I've even heard it happen with vocals though.
I'm not exactly sure what sonic quality lends itself to this; I imagine it's something to do with simpler harmonics? You could record a sine wave at two different times but the summed track would still run into phase issues. One way to address the problem is to alter the guitar tone on the second pass, or change something in the signal path.

As far as checking for phase on each track, it doesn't end up being necessary with experience. You develop an ear for phase problems, even in stereo. That said, always check your mixes in mono, and if you're suspicious, make sure you investigate! Better safe then sorry: some things I always check, like my snare, overheads, stereo acoustic guitar, etc.
Phase cancellation isn't a matter of 'there' or 'not there', it's a matter of degrees. It's a normal part of sound, the problems arise when it sounds unnatural or steals power from your mix.
Old 30th August 2012
  #57
Gear Maniac
 

Quote:
Originally Posted by squirreltrench View Post
That's what phase *is*. A time alignment issue.
That's partially true. Phase, as correctly explained some posts above is a function of time AND frequency. By delaying a signal by a constant time, you introduce a phase shift which is different for every frequency. for example 1 msec of delay will be 360 degrees of phase shift at 1kHz and 180 degrees of phase shift at 500Hz. So you will get some cancellations and some additions otherwise known as comb filtering.

But that is not the whole picture. Your standard analog and digital equivalent filters introduce phase shift as well, but only for some frequencies, while leaving others unaffected. Correction of such phase shifts is much more complicated, just delaying one signal will correct some artifacts, while introducing new artifacts somewhere else in the spectrum.
Your loudspeaker introduces a phase shift throughout most of its frequency range. It delays lows while keeping treble unaffected. The steeper the crossover slopes, and the more crossover legs, the more dramatic the phase shift.
If you played your source acoustically next to your speaker reproducing the source in real time at the same volume, you would get some comb filtering in the lower frequencies.

In case of the poster who asked about his overheads and kick tracks, simple time alignment will fix 90% of the problems. Overtones propagating from the entirety of the bass drum will be picked up by the close microphone at different time intervals than by the overhead. That's because bass drum is a 3D object and paths from vibrating parts of it to the various microphones vary.

And finally, because it always bugs me when people use the terms interchangeably , polarity is NOT phase.
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