Use the Phase Analysis panel
Learn the two primary causes of phase issues and how to fix out-of-phase audio clips using the Phase Analysis panel and the Phase Meter.
Published
Sometimes audio can be out of phase.
So in this lesson I'm going to explain what that means and point out some of the problems that come up, when you have audio that's out of phase.
I'm going to show you how you can use a couple of tools inside Audition CC to detect whether audio is out of phase.
And then finally I'm going to show you how to fix it.
A tall order for one lesson.
So let's get started.
First of all, I talk about audio being out of phase.
What do I mean by that?
Well, there are a couple of ways that audio can be out of phase.
The most frequent circumstances when the audio channels are out of alignment.
Their timing is off.
That can happen when you've got a tape record head that's a little bit out of alignment, so it records one channel ahead of the other one slightly.
And we're talking microseconds here, millionths of a second.
So it's a little bit off.
Or you might have microphones with distinctly different cable lengths that cause timing to be a little bit off for one channel and another.
Or you might record an old monaural vinyl record with a stereo pick up.
And the stereo pickup might get things out of whack because of how it works.
So you end up getting channels that are just a little bit out of alignment which may not even be noticeable.
But it's important to get them in alignment if anyone's going to listen to your product in mono.
And that's going to happen in FM stereo signals, for example.
In the United States most FM stereo signals are broadcast using what's called mid-side.
The mid frequency is actually a monaural frequency with the left and right channel blended together.
And the side frequencies they're subtractive.
And so when they're put together, you end up getting 2 separate channels.
But if you're right on the edge of the receiving area for an FM station, the first channel falls off as the side channel.
So you end up getting a monaural signal.
And if there are phase problems to that monaural signal then it will sound bad.
In stereo phase problems are less obvious, but they show up in terms of the phantom center, where you've got something centered between the 2 channels.
And it seems to be moving around the room a lot.
Or you hear drums kind of moving around the room as they're being played.
Things like that happen, when you're out of phase in stereo.
So how do you detect things that are out of phase?
Well, there are 2 tools inside Audition CC: the old Phase Meter.
And a new tool in the latest version of Audition CC called the Phase Analysis panel.
Let's take a look at the Phase Meter.
To find that we go Window, Phase Meter.
That shows up down here.
You can barely see it.
I'm going to stretch it out a bit here like this so you can see a little bit.
You know something is in phase when you're over here in the green; out of phase anything to the left there.
Let's just take a look at this clip here.
This one's out of alingment.
The timing is off by a little bit.
You can see it's hovering the right side, but not completely.
So something is wrong here.
And this is indicating that something is wrong.
Now take a look at this one here, where there's actually an inversion problem.
Let's take a look at this one.
It shows it's way off here.
Here's a balance issue and it'll show that.
Nothing is wrong there, just a balance problem.
But that's the Phase Meter at work there.
But the Phase Analysis tool gives you a lot more verbose information.
Let's take a look at that one.
Window, Phase Analysis.
It's a whole panel here.
Let's take a look at that.
I'm going to go back to phase-timing.wav here.
There are a few different ways that you can view things here inside the Phase Analysis panel.
So what I like to work with is the histogram here.
There's 3 different kinds of histograms in terms of how they're displayed.
I go for the log zoom version.
These 3 things are a little more technical.
There's the mid-side I was telling you about with the FM signal.
Like that.
But I kind of like the histogram.
And I also like to work with the Phase Wheel.
Now if I look at the histogram here, when things are out of phase, this little green ball drops below the line.
You can see that it doesn't look like it's really out of phase there.
If I go to the Phase Wheel, Phase Wheel shows things that are out of phase if this little line curves around.
And you can see it's really curving around a lot here.
What this shows is timing.
If a line goes straight up that means everybody is in alignment.
If it starts wrapping around like that, that means that the timing is off.
The red colors here are the base frequencies.
And then you go up toward the high frequencies, the treble frequencies here.
If you wrap around once, that means you're off by basically one wavelength.
And so in low frequencies the wavelengths are kind of long.
They last for a longer time than high frequencies.
So if you're off by just a small amount, the bases are not off by much.
The higher frequencies are off by quite a bit more.
So if you're off by maybe 10 samples out of 44,000 samples per second, you're off by 10 samples.
And you're going to be wrapped around here a couple of times.
You're going to be off by more than 2 cycles in terms of the frequency, of the high frequency rate.
You can see it's kind of wrapping around here, because we're off by more than a few samples here.
Let's take a look back at the Histogram (Log Zoom).
The histogram has this option, where you can right click on the center and change the view.
It's the only one that has that.
I'm showing the Ball and the Labels.
I can show other things too, like Tracers, and Peaks and Valleys, but I like to work with just the labels and this little ball.
The ball indicates, whether something is out of phase in terms of inversions.
So I'm going to change to inversion here.
You can see that it's below the line here.
That means one channel is inverted.
I'll show you what I mean in just a moment.
When I talk about balance, it shows whether things are kind of leaning the right channel or left channel.
And here it's the right channel.
Let me go take a look at these things in a little more detail.
Now let me go to the timing first.
And right now you see the timing... ...doesn't show up as any real problem there.
But if I look again at the Phase Wheel you'll see that the timing... ...was really out of whack here.
You can see it by zooming in on the waveform here.
So let's just right-click here and drag.
Kind of zoom in.
Do it again.
Now you can begin to see things here.
I'm going to click here at that peak right there.
You can see that we're a little bit off here.
If I go to the low peak it might be easier to see.
That low peak is a little bit to the right of that low peak.
I'll zoom in some more here.
Like that.
Here's the bottom of the peak there.
And here's the bottom of the peak there.
Let me zoom out a little bit so you get a better look at it.
Things are just a little bit out of alignment by that distance.
So I'm going to go from right here, let's say, right about there.
And that's the distance that it's off.
Right about that.
If you look down here for the duration, I set this to Samples.
The normal setting is to be at Decimal (mm:ss.ddd) like that.
And the duration of, let's say, 4 samples won't even show up.
This is a thousandth of a second.
We're talking millionths of a second here.
Let's change back here to Samples by right clicking and going to Samples.
We're off by about 4 samples here in that little section there.
That's just kind of a rough guess based upon my zooming in here.
And so we can adjust this using the Automatic Phase Correction effect.
So to fix that, I go to Effects, Noise Reduction / Restoration and go down to Automatic Phase Correction...
And inside here you've got the Global Time Shift.
If I click on that we could try to figure out how many microseconds that thing is off.
To do that, I would divide four into 44,000, which would be 1/10,000.
I can convert that to a millionth, which would be about 1/100,000,000.
I'm not going to do that here.
I've got to do it automatically.
So I'm going to turn off Global Time Shift and go for Auto Align Channels.
I'm going to take the default settings here by clicking on (Default).
And we'll click Apply to the whole thing here.
Let's see if things line up.
There you go.
You can see they lined up really nicely right there.
Everybody is now showing that things are in alignment.
And look at this guy.
He's saying: "Yep, nice job."
It wiggles around a little bit because of the vibrato of the organ, but you can see it's going straight up like that.
So we took care of timing by looking at the Phase Wheel, and seeing it was off.
We could see it was off by a few samples here.
Then we fix that by using the Automatic Phase Correction effect.
Alright; that's timing.
Let's take a look at inversion.
Double-click on this.
This shows an inversion too.
You see it's pointing down.
Right off the bat.
Something is wrong, when you see the red line going down.
It's more obvious if you go take a look at the Histogram (Log Zoom).
It's way below the line like that.
If it occasionally drops below the line, that's not a problem.
It happens a lot with drums that occasionally drop down below like that.
But this is down there consistently.
So what does it mean to be inverted?
Well, what happens is that one waveform here is facing the wrong direction.
It's basically cancelling out the other waveform.
Now you still hear the sound, because there's enough other stuff going on that not everything is cancelled out, but some of it's cancelled out.
So let's zoom in on one of these guys here to see that at work.
A little bit more by right-clicking and dragging.
And you can see, look at that, right there, very obvious.
It's going up.
The other wave's going down.
So this channel down here is inverted, which can happen sometimes with wiring.
Also can happen when I'm trying to demonstrate something.
Then I do it on purpose.
So let's just take a look at this right channel here.
I'm going to select just the right channel by hovering my time selection tool here I got that little R in the lower right hand corner.
Click there to select this, the right channel.
And I'm going to invert that to have it go back in place.
And to invert it I go to Effects, Invert.
Now we're back in place.
And now you can see we're happy over there.
Green ball is now above the line.
Take a look at the Phase Wheel.
It too is now pointing up.
Drums do funny things.
So don't worry about the fact that it's rapping all over the place.
That's alright.
But there you go.
We have now fixed the inversion.
Let's take a look at one more thing.
And that's Balance.
Now here I'm balancing.
Looks like everything's fine.
I'll zoom out all the way there.
Take a look at this.
Here in the Phase we're doing great.
If I take a look over at the Histogram (Log Zoom), you'll see that we're kind of aiming for the right a bit.
We're heavily weighted in the right channel.
Which may be exactly what you want.
I mean this is not necessarily wrong, it's not really truly a phase problem, but you may want to have things centered up when you're done working on this thing.
So you can use this tool not only here in the waveform view, but also in the multitrack session on the master channel.
And it'll show you exactly what's going on.
So you might want to adjust your balance when you're done working on something to make sure that things are basically centered up, so things are not leaning left or leaning right.
So in this case, we can correct this by just increasing the volume of the left channel to compensate for the fact that we got a lotta here on the right channel.
Or I could reduce the right channel.
Let me select the left channel here by hovering at the top and selecting that channel.
I'm going up to the volume control here, raising up a bit.
Say maybe 3.5.
And now we'll check that out.
I went a little bit too far there probably.
So let me undo that.
Ctrl / Cmd Z.
I'm typing; the left channel is 2.5 here.
2.5.
Try this now.
See how that works.
It's a little bit to the left.
I could maybe make it 2.3, something like that, but you can see that we've now made that adjustment.
So that's how you can use this really cool Phase Analysis panel to determine whether things are out of phase in terms of timing, inversion or balance, and then how you can fix those things.
Contributor
