Phase Question??

[bohunk06]

I know what phase means when recording. I understand what it does if things are out of phase an all that. But my question is...and this may be dumb... is what is the importance of getting it right when tracking if I can just go in and reverse phase in the program. Does that not accomplish the same thing? I have been reading so much lately about getting mics placed right to avoid phase problems. For example, drum overheads... but can't I switch them later in the program if one is out of phase?

Thanks for any help!

 

[SouthSIDE Glen]

I know what phase means when recording. I understand what it does if things are out of phase an all that. But my question is...and this may be dumb... is what is the importance of getting it right when tracking if I can just go in and reverse phase in the program. Does that not accomplish the same thing? I have been reading so much lately about getting mics placed right to avoid phase problems. For example, drum overheads... but can't I switch them later in the program if one is out of phase?

Thanks for any help!

Reversing phase electrically or in software is simply change the phase by 180°. Those won't help much if your two sources are out of phase by, say, 105° or 270° or any other significant amount that far enough away from 180°

G.

 

[bohunk06]

Oh I see.... I guess I didn't know that phase could be off by 105 or 270 or any other amount. I figured 180 was it. I will pay more attention to phase going in.

Thanks Glen!!

 

[mattr]

The phase button isn't a magic button.
I was having a conversation with a friend-of-a-friend at a New Year's party who was supposedly very knowledgeable in all things recording having just complete his A-level music-tech course . Anyway, I was telling him how I'd just been recording some guitars and layered each part several times which he seemed very confused about and asked why I didn't just duplicate the track, pan them hard L/R and delay one a bit. I told him that it didn't quite have the same effect as layering, and it thinned out horribly when you summed to mono. To this he replied... 'not if you press the special button in Cubase'. This was also the same guy who asked me why I varied my mic placement when recording guitars - "wouldn't it be better to record all the same then change the tone in post-production?"... *lol*. And yet, after all this, he still thought he knew more than me

Annnyyyway, back on topic.
The phase button just inverts the phase. And example where to use this is when you double-mic a snare and the mic on the bottom of the snare will be out of phase with the one on top (to put things simply) because they are on either sides of the sound source facing each other. In this case, yes, you make sure that you invert the phase.
Another time you would use the button would be if you had a cable that had been wired wrong and so one of the channels of a stereo signal / double-mic / mic+DI recording had been inverted.

However, the phase issues encountered with things like drum overheads are caused by time differences...

If you have a snare drum with one mic next to it and one mic across the other side of the room, there will be a slight delay between the sound reaching the first mic and the second mic. Now think back to your drum overheads - if you have a spaced pair then sound (maybe of a snare hit) may arrive at one mic slightly before the other, which could cause some weird cancellation when they are summed (well, not if they were panned hard and not actually being summed, but it could still sound a bit odd).

You can't just delay tracks to make them 'line up'; you could line up some back overhead tracks to make all the snare hits in phase but it would push everything else out and probably make something else like cymbals or toms sound really weird. It would sound even more weird if you had some room ambiance in the recording which got messed around by delays.

So yes, get it right in tracking.
Enjoy

 

[RAMI]

Aside from all that, if you know (or even worse, if you don't know) that your drum overheads are out of phase, how you can you judge whether or not you're getting the best possible sound at the tracking stage, since it changes the sound.

If you believe getting the sound right at the source is important, then you should be doing everything you can to ensure you're getting the best possible sound at that stage, rather than just throwing up a couple of mics and hoping you can fix it in the mix later. Chances are, if you don't care whether they're in phase or not, then you must also not care about about whether you're capturing the best possible sound with those same mics. There's more to tracking properly than just phase relationships.

 

[bohunk06]

I understand what you all are saying. Thanks for the replies. But is getting the phase right done by simply listening to the track for odd sounds? I mean, I know it has to do with how far each mic is from the source. Different distances will cause issues. But say I think I have that all correct, is there a way to tell, other than by ear, if they are out of phase? Is looking to see if the sound waves line up the way to do it? Or is it all done by a careful listen to the tacks?

Thanks guys!

 

[RAMI]

I understand what you all are saying. Thanks for the replies. But is getting the phase right done by simply listening to the track for odd sounds? I mean, I know it has to do with how far each mic is from the source. Different distances will cause issues. But say I think I have that all correct, is there a way to tell, other than by ear, if they are out of phase? Is looking to see if the sound waves line up the way to do it? Or is it all done by a careful listen to the tacks?

Thanks guys!

You can use your eyes AND your ears. But, an out of phase sound is usually thinner and just.......weird. You should be able to hear it.

 

[mattr]

Listen for a thin sound, an awkward-sounding stereo image (feels 'skewed' or unnatural), or a strange 'shimmering' on cymbals.

 

[NL5]

The "phase" button is actually a polarity button.......

 

[SouthSIDE Glen]

The "phase" button is actually a polarity button.......

You have no idea how happy I am that I managed to restrain myself from saying that long enough for someone else to say it for a change . It's your baby now, NL .

G.

 

[tvolhein]

The "phase" button is actually a polarity button.......

http://www.musiciansfriend.com/document?doc_id=91427

 

[bohunk06]

http://www.musiciansfriend.com/document?doc_id=91427

That was a great article. Thaks for sharing. That definitely helps me understand a little more. So, is it safe to say that even if I track something out of phase that I can fix it by just nudging the tracks so that the waveforms line up? Like in that 3rd illustration ("phase shift"), if I were to just nudge one track to line up with the other, I would be good to go?

Thanks!!

 

[MCI2424]

The "phase" button is actually a polarity button.......

The "polarity" button is actually a switch............

 

[Sonixx]

I know what phase means when recording. I understand what it does if things are out of phase an all that. But my question is...and this may be dumb... is what is the importance of getting it right when tracking if I can just go in and reverse phase in the program. Does that not accomplish the same thing? I have been reading so much lately about getting mics placed right to avoid phase problems. For example, drum overheads... but can't I switch them later in the program if one is out of phase?

Thanks for any help!

yes, you can. this is exactly what I do with the setup below. I often track two mics on a guitar cab (to create a mono mix) and shift them in time and use that as an EQ. It can work wonderfully and achieve results not otherwise achievable. This setup allows a minimum shift of one bit. Another way to look at it is an inch difference is basically 3.73 bits at a 44100 sample rate.

Some clarity is in order... It was stated earlier about two sources being out by 105° or 270°. One can't look at complex waves (anything other than a pure since wave and complex waves are made up of sine waves of many different frequencies and amplitudes (See FFT)) this way. A complex wave cannot be 105° or 270° out from each other. Individual specific frequencies within the wave can be but not the wave as a whole. Shifting two complex waves in time (e.g moving one mic relative to another) results in no two frequencies seeing the same relative shift amount. i.e. 1KHz and 1.1KHz will create two totally different phase shift results.

IMO, getting a real handle on this allows one to use this to your advantage and can be a great tool.

 

[bohunk06]

Ok, I kind of get what you are saying. If I sum that up, moving a complex wave as a whole may not move all the individual frequencies the same amount. Which might put low frequencies in phase, but put high frequencies out of phase (as an example)? Is this correct? So this still doesn't really answer the question.... If I see something is out of phase by looking at the waveforms, do I just do the 180 polarity switch or do I nudge them to line up or am I S.O.L. at that point?

Thanks!!

 

[Sonixx]

Ok, I kind of get what you are saying. If I sum that up, moving a complex wave as a whole may not move all the individual frequencies the same amount. Which might put low frequencies in phase, but put high frequencies out of phase (as an example)? Is this correct? So this still doesn't really answer the question.... If I see something is out of phase by looking at the waveforms, do I just do the 180 polarity switch or do I nudge them to line up or am I S.O.L. at that point?

Thanks!!

Note that this is only an issue with two waves that are coherent i.e. tracking the same source.

Don't adjust by looking.... Adjust solely by listening.

here's an exercise, record something with two mics aligning phase as closely as possible by hand. record a stereo track.

next put something like Sample Delay on the track.

set the final output (main buss) to Mono

next invert the track's Left Side

now using Sample Delay adjust the left side or right side (select the side that is the closest to the source, one will be) to delay.

adjust for the least volume and least treble

now un-invert the inverted side

what happens is with the least treble inverted, you'll have the most treble normally because those frequencies are relatively the most in phase and add. frequencies that are relatively out by some amount cancel by some amount.

now using Sample Delay move one side relative to the other, you'll find this acts like an EQ because different frequencies are canceling and adding in differing amounts.

one thing that can happen is when frequencies cancel in such a way that Comb Filtering becomes very evident thus causing that ringy-nasally tone.

 

[SouthSIDE Glen]

Some clarity is in order... It was stated earlier about two sources being out by 105° or 270°. One can't look at complex waves (anything other than a pure since wave and complex waves are made up of sine waves of many different frequencies and amplitudes (See FFT)) this way. A complex way cannot be 105° or 270° out from each other. Individual specific frequencies within the wave can be but not the wave as a whole.

Yeah, you're right that a time delay-based phase shift of a complex wave cannot be accurately measured as a set degree. I did somewhat misspeak there.

In fact the "phase" (actually polarity) button, being time-independent, effects an instantaneous phase rotation of 180° (yes, even on a complex wave). Whereas the phase problems between two microphones are the type caused by a time shift, not a phase rotation, so referring to those with different numbers was incorrect of me.

But it does still illustrate the essential concept here; that phase change - whether shift or rotation - is not simply bi-polar like polarity; either positive or negative, either 0° or 180°, but rather can vary by differing amounts, and a simple either/or button can't address that.

G.

 

[SuaveRecords]

QUESTION:

When im having phase issues, i just flip the phase, and then zoom in very tight on my waves (for example top and bottom snare mics) and i nudge the one wave slightly until it matches the other one. after doing this i can actually hear a fatter snare with much more beef to it. so my question is, dose nudging the one wave and lining it up with the other actually work well? or am i just hearing things? or is there hardware/software that would do a better job of it? and dose nudging them until they LOOK in phase actually work as well as it visually seems to?

 

[NYMorningstar]

...Anyway, I was telling him how I'd just been recording some guitars and layered each part several times...

How do you layer a guitar track exactly?

...
If you have a snare drum with one mic next to it and one mic across the other side of the room, there will be a slight delay between the sound reaching the first mic and the second mic.

Wouldn't the distance being the other side of the room make this a non-issue?

...
Now think back to your drum overheads - if you have a spaced pair then sound (maybe of a snare hit) may arrive at one mic slightly before the other, which could cause some weird cancellation when they are summed (well, not if they were panned hard and not actually being summed, but it could still sound a bit odd).

What happens if I use a supercardioid mic?

 

[Sonixx]

so my question is, dose nudging the one wave and lining it up with the other actually work well? or am i just hearing things?

yes, you are just hearing things... which is the way you adjust this. resist the temptation to use your eyes as the main input. yes, you may want to initially get them aligned visually, but then let/make your ears take over.

slightly moving one wave causes some frequencies to cancel and some to add.

move one wave until the sound/tone fits best and adjusting relative levels

regardless, there's no substituting getting the best tone with mic positioning for both. because the top mic is X distance does not mean the bottom mic should be X distance. referring to my earlier post, you can align post tracking to achieve the best possible.