Old 27th June 2006
  #1
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Phase Scope

I've been wondering what a phase scope is and how it is used to help engineers. I listened to several of my finished songs and then some Steely Dan, Third Eye Blind, Bob Marley and Pink Floyd while watching the phase scope and a spectrum meter. I noticed that during Pink Floyd, Us and Them that the small little indicator at the bottom of the phase scope that skips around between -1 and +1 stayed closer to 0 than with the other songs. My song tended to bounce narrowly around on the +1 side.

I'm including a link to some video I shot of what I'm talking about so you can see it. The -1/+1 indicator is on the bottom of the phase scope on the upper left hand corner of the screen. It’s pretty interesting to watch the spectrum meter and the phase scope while listening to Us and Them. After you click on the link, hit the pause button on the video player and wait about a minute depending on your internet connection to allow the video to load. You can move your curser to the time line of the video, (your cursor will turn into a hand) and slide the diamond shape all the way to the left to start the video from the very beginning and then hit play.

I did a little research online but couldn't find too much on phase scopes as they relate to sound engineering. I would be grateful to any of you professional/expert Gearslutz that have some real knowledge of this to share your expertise.

Thanks,


bcgood

http://www.youtube.com/watch?v=sYVqOioJwOE
Old 27th June 2006
  #2
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Cojo's Avatar
 

Hi.

When the meter shows +1 you have a stereo signal perfectly in phase. If it shows - 1 you have a stereo signal 180 degrees out of phase. If it shows 0 then you have a mono signal.

Easy as that!

/Cojo
Quote
1
Old 27th June 2006
  #3
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lasso's Avatar
 

Ehmm..it's + 1 for mono, 0 for "absolute stereo" and -1 for absolute out of phase huh?
Old 27th June 2006
  #4
Gear interested
 

You're absolutely right Lasso, Cojo's got it wrong:

+1 shows exact phase coherence between left and right i.e. mono

-1 shows exact phase incoherence between left and right i.e two identical signals out of phase with each other.

0 shows no phase coherence at all between the left and right sides.

On a mix, the nearer you are to +1, the closer you are to mono.

The nearer you are 0 (without going below it preferably), the more 'stereo' or 'wide' your mix sounds. Records with lots of reverb will get closer to this for example.

It used to be a no-no to go below 0 when you were cutting vinyl as the lathe couldn't cope. With CD it's not an issue, so the odd dip below 0 is fine if you have some out-of-phase content, but bear in mind that if it is summed to mono then things will disappear.

Wes
Old 27th June 2006
  #5
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Quote:
Originally Posted by weslryt
You're absolutely right Lasso, Cojo's got it wrong:

+1 shows exact phase coherence between left and right i.e. mono

-1 shows exact phase incoherence between left and right i.e two identical signals out of phase with each other.

0 shows no phase coherence at all between the left and right sides.

On a mix, the nearer you are to +1, the closer you are to mono.

The nearer you are 0 (without going below it preferably), the more 'stereo' or 'wide' your mix sounds. Records with lots of reverb will get closer to this for example.

It used to be a no-no to go below 0 when you were cutting vinyl as the lathe couldn't cope. With CD it's not an issue, so the odd dip below 0 is fine if you have some out-of-phase content, but bear in mind that if it is summed to mono then things will disappear.

Wes
I don't understand where I got it wrong!?

I was saying the exact same thing in a different way! Read again! A stereo signal in phase is a phantom mono. If you take a true mono (only one channel) it will show zero!

/Cojo
Old 27th June 2006
  #6
Mastering
 

Quote:
Originally Posted by bcgood
I've been wondering what a phase scope is and how it is used to help engineers. I listened to several of my finished songs and then some Steely Dan, Third Eye Blind, Bob Marley and Pink Floyd while watching the phase scope and a spectrum meter. I noticed that during Pink Floyd, Us and Them that the small little indicator at the bottom of the phase scope that skips around between -1 and +1 stayed closer to 0 than with the other songs. My song tended to bounce narrowly around on the +1 side.
Good that you noticed that! This means that your material is largely mono. The further to the right (closer to +1) the more monophonic your material is. The center (middle of the meter, 0 point) is where the ambience, the space and the depth lie, with occasional very brief excursions to the left "permitted". Now, I'm not saying to mix by the meter, but the correlation meter can be an excellent teaching tool in the beginning to those who are looking to see how much uncorrelated material there is in their mixes. After a while you begin to recognize "that sound" and you won't need the correlation meter any more, though you should check periodically with your monitor in mono to see if there are any cancellations.
Old 27th June 2006
  #7
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macr0w's Avatar
 

What program are you using to get that meter? The only phase scope I have is the BombFactory meter that comes with ptle. I don't know how reliable it is. I also have Wavelab 5. Is there a good meter in Wavelab? What other plugins can you recommend?
Old 27th June 2006
  #8
Gear interested
 

Quote:
Originally Posted by Cojo
I don't understand where I got it wrong!?

I was saying the exact same thing in a different way! Read again! A stereo signal in phase is a phantom mono. If you take a true mono (only one channel) it will show zero!

/Cojo
OK, I read it again and I'll amend my response: it was misleading rather than wrong. When the phase meter shows 0 it indicates that there is no phase correlation between the left and right outputs of a console (which is where it is usually used). Therefore if you pan any signal hard left and there is no signal in the right channel then the phase meter will sit at 0 as there is no phase relationship between signal and no signal.

However, what most people want to use a phase meter for is to see how mono/stereo/out-of-phase their mix is. So to say that 0 shows a mono signal is misleading...

Also your reply is misleading. 'A stereo signal in phase is phantom mono' describes a mono signal that has been panned equally to both left and right outputs of a mixer: panned mono and stereo are not the same thing. 'True mono' is a meanlingless term in the context that you are using it; mono is mono wherever it is panned in the stero field, it's simply sharaing that mono signal between two outputs.

Sorry to be pedantic, but it's important to be clear.

Wes
Old 27th June 2006
  #9
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Zeppelin4Life's Avatar
 

The one in Wavelab is cool. It works, anyway. A phase scope can help you find phase problems. I remember I had a mix that was crazy out of phase, and the scope looked like a worm moving all around. That's not good. It was going in and out of phase everywhere. If the mix is 180 degrees out of phase (a polarity of a channel is reversed), in theory the graph should be totally horizontal on the X axis. If it's totally in phase, it should be totally vert (on the Y axis). This is only theoretical. That is why only mono will ever be 'perfectly in phase'. Thats how stereo works, it's not perfectly equal on either side

rock on
Old 27th June 2006
  #10
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Cojo's Avatar
 

Quote:
Originally Posted by weslryt
Sorry to be pedantic, but it's important to be clear.

Wes
It's ok!

I am really bad at explaining things, good I'm not a teacher!

/Cojo
Old 27th June 2006
  #11
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Please bear with a novice for a moment. After reading this thread I loaded a recently recorded 16 bit 44.1 sr stereo .wav file into wavelab and pulled out the phase meter. Now the meter bounces around in the middle between the 0 and the +1.

So that tells me according to the above posts that my song is closer to mono than true stereo. This track was recorded on only 5 tracks (4 mics and a di from acoustic bass). The band was recorded live and all playing at the same time.

How does this happen? Is it from mic placement? Or my awesome mixing technique? Is there anything I can do to this recording to make it closer to "true stereo"?

Like I said I'm just a novice and don't have alot of expirience dealing with phase issues. Or should I say "correcting" phase issues. Thanks for any help you could pass along to an ametuer.
Old 27th June 2006
  #12
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Thread Starter
Thanks Weslryt and Bob, those responses help the most. That's interesting stuff. Like you said Bob, I don't want to solely use and mix by the scope but it's another tool to analyze my stuff and try to dial it in. It’s interesting because my signal really mostly stays vertical and thus according to you’re guys information it means it’s in phase and contains somewhat mono characteristics. But the song has some fairly strong panning. For instance my high hat is all the way to the right and my kick is even panned a little left. I might have lost some of that when I limited it? I was trying to make the mix a little louder for people listening to it on the internet. I don’t have an album done yet; if I did I would let someone master it. I used the limiter in Wavelab with a 10ms release and then hard limited it in Cool Edit Pro further. Another thing that I notice with my song is that the spectrum meter shows almost all of the energy on the lower (bass) section even though it sounds somewhat “bright” to me…

bcgood

P.S. The video I took is of Wavelab...
Old 27th June 2006
  #13
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Zeppelin4Life's Avatar
 

Quote:
Originally Posted by macr0w
Please bear with a novice for a moment. After reading this thread I loaded a recently recorded 16 bit 44.1 sr stereo .wav file into wavelab and pulled out the phase meter. Now the meter bounces around in the middle between the 0 and the +1.

So that tells me according to the above posts that my song is closer to mono than true stereo. This track was recorded on only 5 tracks (4 mics and a di from acoustic bass). The band was recorded live and all playing at the same time.

How does this happen? Is it from mic placement? Or my awesome mixing technique? Is there anything I can do to this recording to make it closer to "true stereo"?

Like I said I'm just a novice and don't have alot of expirience dealing with phase issues. Or should I say "correcting" phase issues. Thanks for any help you could pass along to an ametuer.

A mix will never be +1 unless it is mono. A mix will never be -1 unless it is completely out of phase (and you wouldn't hear anything...it would totally cancel out)...between 0 and -1 is 'out of phase'

between 0 and +1 is good and normal
Old 27th June 2006
  #14
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Cojo's Avatar
 

Quote:
Originally Posted by macr0w
Please bear with a novice for a moment. After reading this thread I loaded a recently recorded 16 bit 44.1 sr stereo .wav file into wavelab and pulled out the phase meter. Now the meter bounces around in the middle between the 0 and the +1.

So that tells me according to the above posts that my song is closer to mono than true stereo. This track was recorded on only 5 tracks (4 mics and a di from acoustic bass). The band was recorded live and all playing at the same time.

How does this happen? Is it from mic placement? Or my awesome mixing technique? Is there anything I can do to this recording to make it closer to "true stereo"?

Like I said I'm just a novice and don't have alot of expirience dealing with phase issues. Or should I say "correcting" phase issues. Thanks for any help you could pass along to an ametuer.
I don't think I should try to explain this to you (thinking of my earlyer attempt) but here it goes...

Only because the needle is at +1 it doesn't mean it is not stereo. It means it is pefectly in phase. If it's point at the 0, the chanels are 90 degrees out of phase of each other or one channel is silent and one has signal. If it is in -1 the channels are 180 degrees out of phase.

Does this makes any sense or should I practice more on my educational skills?

One thing one can do is to take a sine wave and move one channel forward or backward agains the timeline and see what happens.

/Cojo
Old 27th June 2006
  #15
Gear interested
 

To answer Cojo first:


Quote:

Only because the needle is at +1 it doesn't mean it is not stereo. It means it is pefectly in phase. If it's point at the 0, the chanels are 90 degrees out of phase of each other or one channel is silent and one has signal. If it is in -1 the channels are 180 degrees out of phase.


If the needle is at plus one, it does mean that it is not stereo. As you rightly say, it means that there is perfect phase coherence between the two channels, which means that they are the same thing, which, by definition, means that they are mono: the same signal coming out of two speakers is mono.

You are right that at -1 the two channels are 180 degrees out of phase. But if the needle is at 0 it doesn't mean that the two hannels are 90 degrees out of phase; [life is just not that simple :-)] it just means that there is no phase correlation between them.

To answer macrOw:

Quote:

So that tells me according to the above posts that my song is closer to mono than true stereo. This track was recorded on only 5 tracks (4 mics and a di from acoustic bass). The band was recorded live and all playing at the same time.

How does this happen? Is it from mic placement? Or my awesome mixing technique? Is there anything I can do to this recording to make it closer to "true stereo"?


First, forget the phrase 'true stereo' in this context, a phase meter does not indicate true stereo, it just indicates on a sliding scale whether the mix is mono (+1) to very wide stereo (closer to 0) through to out-of-phase (-1).

In terms of your mic placement, a stereo miking setup will produce varying results on a phase meter. If you employ a coincident pair (capsules placed close together) the phase meter will be hovering nearer +1 as there is a high degree of phase correlation. The sound that you hear (when you sit between correctly positioned speakers) will be a stereo soundfield that is nice and focussed in front of you. However, if you use a spaced pair of mics, there will be less phase correlation so the needle will still be in the positive area but nearer to 0. The sound that you hear will be wider, more diffuse, less focussed.

So just mix so that it sounds good to your ears, experiment with mic positioning as much as possible, place your speakers carefully (in an equilateral triangle with your head) and just use the phase meter as a guide, particularly in helping to identify out-of-phase material.

Wes
Old 27th June 2006
  #16
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Zeppelin4Life's Avatar
 

Quote:
Originally Posted by Cojo

Only because the needle is at +1 it doesn't mean it is not stereo

/Cojo

this is true. However, by definition, if the two channels are completely similar, it is not stereo....or at least, it would sound exactly the same as mono.
Old 27th June 2006
  #17
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Cojo's Avatar
 

Quote:
Originally Posted by Zeppelin4Life
this is true. However, by definition, if the two channels are completely similar, it is not stereo....or at least, it would sound exactly the same as mono.
Yeah I know, I give up!

weslryt - You're a good man, I mean no harm...

/Cojo
Old 27th June 2006
  #18
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Yeah man..no hard feelings to anyone..thats how we all learn, right?

all these numbers and phase relationships are all theoretical. In normal human music, you are never going to get 'perfect phase'. Phase difference makes stereo depth...someday hook your CD player thru a mono Y-cable into the stereo system and flip the phase of one of the speakers....now theres some fun. seriously. everything that was 'perfectly in phase' or 'mono' in the center of the track goes away, so all you can hear is stuff on the sides.


by the way, i've never heard of anyone getting a '0' in phase on the -1 0 +1 chart unless they're going MS mode
Old 6th August 2006
  #19
So let's say I have a pair of condensers over a drum kit will it hurt if they are spaced and the meter reads between 0 and +1? Will it suck in mono?

V
Old 6th August 2006
  #20
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jenkel16's Avatar
 

Quote:
Originally Posted by Nu-tra
So let's say I have a pair of condensers over a drum kit will it hurt if they are spaced and the meter reads between 0 and +1? Will it suck in mono?

V

Only if it sucks in stereo.
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