Phasing--Let's Talk About This

[crawdad]

I've been pondering all this phase talk and would like to get a clearer understanding of how its tossed around here. First, I do understand phase cancellation and how that works--two like waveforms in the same place in a mix will cancel each other out completely if they are at the same volume or amplitude. If you lower the volume of one of those waveforms, there will be less phasing. So far, so good.

Here is where I lose the concept--when the subject of phasing and EQ comes up. My first question is how can one waveform going through an EQ cause phasing problems?

Does the EQ cause some kind of delay to the part of the signal that its applied to? Or--maybe--is EQ actually kind of like using selective phasing to cancel out only certain bands? What am I supposed to be listening for exactly?

I've also heard people describe the phenomenon of different tracks being slightly out of sync and saying they hear phasing. That really throws me off the track. In my mind, out of sync and phase are two different issues.

As you can see, I'm in need of a bit of help on this whole thing.

I was gonna ask how Santa Claus is able to go around the world in one night, but unless he uses some special phasing method, I'll save that for another day.

 

[ambi]

yea im confused on this too, i think this would be an excellent thread to help us understand, so come on people! your all so smart you know you want to show off!

I've also been confused about mic placement and knowing when you'll have phase problems, and how to hear them and fix them. Also i was recording with a Mackie 1202 board, and as far as i could tell, i didn't have any phase reversal buttons, so how would you reverse the phase on a mic?

 

[mixmkr]

. Also i was recording with a Mackie 1202 board, and as far as i could tell, i didn't have any phase reversal buttons, so how would you reverse the phase on a mic?

one easy way would be to make a special cable or box, in your situation, and reverse the wiring from the "input" to the "output" or pin 2 and 3 on your xlr cable on the opposite end.

and as far as the EQ issue, I believe there is a latency issue, however slight. Being out of sync can cause phasing problems too. Remember how the phasing sound was orginally derived...with the tape deck (and a digit...thumb!), and in a sense one of the signals was out of sync...or not exactly in time with the other.

 

[crawdad]

Well, Ambi, while we wait for the gods of recording knowledge to show up, I can partially answer your questions.

In regard to changing the phase of a mic using your 1202, there is a way. You have to rewire one end of the xlr cable. By reversing two wires, you have a cable that reverses the phase. Only problem is that I can't remember which two of the three you change! I'll try and find out.

Another way is to reverse the phase in your computer recorder, if you are using a program that allows you to do this.

As for mics and phase issues, the 3:1 Rule is common practice to avoid phase cancellation. It means that the mics should be three times farther apart than they are from the sound source. So, if your mic is 1" away from your drum, the other should be 3" away from the other mic and 1" from the sound source.

If you record a snare drum and mic both the top and bottom heads, you can hear the effect of reversing the phase. Listen to it with both mics in phase and then put one mic out of phase (usually the bottom if you are using multiple mics). Its pretty noticable in this test.

Another reason for avoiding phase problems in mutiple micing setups is that everything might sound fine in stereo, but if you play that track in mono, things can disappear altogether!

 

[pipelineaudio]

"My first question is how can one waveform going through an EQ cause phasing problems? Does the EQ cause some kind of delay to the part of the signal that its applied to? Or--maybe--is EQ actually kind of like using selective phasing to cancel out only certain bands?"

you kinda answered your own question. Most EQ's work by using capacitors and inductors to lead and lag certain frequencies. Phase cancellation can be exactly how it works

"I've also been confused about mic placement and knowing when you'll have phase problems, and how to hear them and fix them"

On this page I tell a way that I use to make sure 2 mics on one guitar cab are in phase, but similar technique will work on other things as well, and the principle will follow all multi mic setups:

https://homerecording.com/bbs/showthread.php?threadid=64239&highlight=metal

like the other guys say, a few cables hanging around with pins two and three reversed on one side are VERY handy to have around, even if youre stuff does have phase switches

 

[crawdad]

Ah! mixmkr to the rescue on the pin outs for the XLR. Thanks, man! You saved me some time searching!

OK. I understand the possible latency there, but isn't the sound we know as phasing a product of CHANGING delay times? In other words, its not static--one tape is slowing down and speeding up. If the EQ introduces latency, wouldn't we hear more of a delay effect? I mean, since its a static shift.

 

[crawdad]

Thanks Pipeline and Mixmkr--I may ask some seemingly stupid questions before I'm done(like I never have before!) but I'm just trying to get to a more complete understanding of all this.

I gather that EQ is both our friend and our enemy. The grail is to record things so well that minimal EQ, if any is required. If I take an acoustic guitar and sweep through the frequencies, I hear what sounds like phasing to me--when I am sweeping--or if I take a big chunk and boost it. So, I kind of have a limited clue as to what to listen for.

So, if this phasing thing is bad, is it less bad if you apply a cut to the low end mud on an acoustic, just to get that frequency stuff out of the way? My thought was that things like the bass and kick would mask whatever phasing might be happening there. I am becoming a fan of cuts rather than boosts. Is this in any way less damaging to the audio than boosts?

Also, if the latency is introduced by EQ, my next (very logical) guess is that the better the EQ, the FASTER it processes? Yes?

See, I told you I'd ask a bunch of dumb questions!

 

[pipelineaudio]

the striving for fidelity is a great thing, but sometimes, you WANT the efect of an EQ...its not always to correct, sometimes it IS to effect

 

[mixmkr]

OK. I understand the possible latency there, but isn't the sound we know as phasing a product of CHANGING delay times? In other words, its not static--one tape is slowing down and speeding up. If the EQ introduces latency, wouldn't we hear more of a delay effect? I mean, since its a static shift.

the common thought of effect of phasing IS the changing of relationships between the two sounds combined. However, if there is no change, it is like your phasor has "stopped" so to speak...and the phasing effect is still there, but not changing with time. Brian May in Queen seemed to use that sound alot on his guitar. If you use a computer to record, and have ever monitored and conbined the input and outputs together, you have probably experienced that "hollow" sound also...

the latency that EQ introduces is so much less than something that is more commonly used as a delay effect... Generally, I don't really hear it ....I hear the EQ change more, and cannot really interpret the phasing. In line in a monitoring situation, the idea is it would tend to smear the actual sound, even though you think it is a correction. Next...ask me why my JBL4311 monitors have two "EQ" knobs on them.. the Mackie 824 too...and many others...eh? you say volume knobs?

 

[Light]

First, the reason EQ adds phase issues is because low frequencies are more robust, and can go through the electronics without being slowed down. High frequencies, on the other hand, are slowed by all the electronics in EQs.

Second, there is no such thing as a "phase reversal" switch. Phase is an issue of time. Even if the switch is called "Phase," it is actually changing the POLARITY of the signal. There is a big difference. Check out my post in the following threads:

https://homerecording.com/bbs/showthread.php?threadid=62002

https://homerecording.com/bbs/showthread.php?threadid=57636

https://homerecording.com/bbs/showthread.php?threadid=59380



This should clear up the difference between phase and polarity. It is important, in a situation where you have many people who are new to recording, to use the correct terminology. Professionals frequently use the two terms interchangeably, and in a situation where every one knows the difference, this is fine. Though many people on this board know the difference, there are also many who do not. By using the correct terms, we can help keep things clear.

Lastly, where to put multiple mics is something which can be done best by listening. Use whatever rule of thumb you want to, but then you have to listen. If something doesn't sound right, move the mic. Frequently, reversing the polarity will make an improvement, but not always.

By the way, what we are talking about here is not "phasing", but phase cancellation. Phasing is a specific effect, which is created by inducing phase cancellations in a cyclical pattern. (The finger on the tape flange is flanging.) Phase cancellation is when two sound waves mix together, and the negative signal from one cancels out some or all of the positive signal from the other.

Oh yeah, and if you want to reverse polarity and do not have a polarity switch on your mixer, you can swap pins two and three in a couple of mic cables. You can also get barrels which can have male and female XLR ends on them, and you can wire them in reverse so you don't have to worry about which cables are reversed and which are not.

Light

"Cowards can never be moral."
M.K. Gandhi

 

[mixmkr]

I gather that EQ is both our friend and our enemy. The grail is to record things so well that minimal EQ, if any is required. If I take an acoustic guitar and sweep through the frequencies, I hear what sounds like phasing to me--when I am sweeping--or if


So, if this phasing thing is bad, is it less bad if you apply a cut to the low end mud on an acoustic, just to get that frequency stuff out of the way?

Also, if the latency is introduced by EQ, my next (very logical) guess is that the better the EQ, the FASTER it processes? Yes?

don't mistake the sweeping as phasing...maybe more like a wah wah effect.

yes

yes...

 

[mixmkr]

Light sums it up best... and is using the BEST terminolgy....phase CANCELATION, polarity...etc


and cause yeah.... the tape reels didn't have phases on the edge...but flanges!

 

[crawdad]

Yes, Light has cleared up the terms for me, which was half of what my problem was. What I understood as phasing was something different than phase cancellation. Thank you Light!

Mixmkr--I get the wah wah analogy too. I also thought the source of the word flanging was pretty cool! never struck me before!

First, the reason EQ adds phase issues is because low frequencies are more robust, and can go through the electronics without being slowed down. High frequencies, on the other hand, are slowed by all the electronics in EQs.

Now, this is interesting. So, the idea of cutting lows is a better way to go than boosting or cutting highs. Cool!

and, Pipeline--yeah, I understand that sometimes you want to color something with EQ. I guess I'm just trying to understand the tools in a textbook kind of way first, so I will have more knowledge when I get to that satep of wanting to color something a certain way.

Thanks everybody. I'm gettin' there!

 

[crawdad]

Sorry--I can't format these things worth a damn. I'm BBS illiterate. I'll work on it....

 

[mixmkr]

hey OLD man....you're doing just fine, computer-wize... I think all understand you... except on that BPTTE thing...or whatever it is

 

[crawdad]

Thanks Mixmkr--I enjoy talking with you, Definitely one of the best here! You mean the BBTTE--the triple tube exciter! I have no idea what the BB stands for--ask Chessrock--its HIS invention! I just get a kick out of how companies take a bad product and dress it up with marketing hype. "Oh, COOL! Its got a (faux) tube in it. That'll really warm up my digital. Probably the last piece of gear I'll EVER NEED!"

Anyway, I'm thinking of EQ as a coloring tool and the first thing that comes to my mind is the guitar amp. I do all kinds of cutting and boosting with mine, and I know there is all kinds of phase cancellation, but it creates a desirable tone. Compare a cranked Fender with a direct guitar track--two totally different animals. Oh, I like direct guitar sometimes too.

It got me thinking of the EQ circuits, which are usually just capacitors that go to ground. So, now I'm wondering if those circuits actually introduce those signals back into the original pure sound--that would be selective phase cancellation at its simplest. Or maybe this is the correct idea 180 degrees out of phase!

Whatever. I just want to understand this issue so when I do use EQ, I can have a little theory and understanding of both the good and bad things it can do. Its all in the interest of making better recordings.

 

[crawdad]

Whaddaya mean--OLD!

 

[Light]

Most guitar amp circuits only cut, and at ten they are (in theory) passing a signal unaffected.

By the way, it is always better to cut than to boost with EQ, if you can get away with it. Boosting adds noise, as well as being a bigger problem for phase cancelation.

Light

"Cowards can never be moral."
M.K. Gandhi

 

[crawdad]

Most guitar amp circuits only cut, and at ten they are (in theory) passing a signal unaffected.

By the way, it is always better to cut than to boost with EQ, if you can get away with it. Boosting adds noise, as well as being a bigger problem for phase cancelation.

Light

"Cowards can never be moral."
M.K. Gandhi

Ah! You are absolutely right. The caps act as filters that just drain off certain frequencies. In fact, I have an amp that has a circuit that gradually decouples the tone stack from the amp and when the tone stack is dialed out, its just like all tone controls on ten.

The idea of cuts rather than boosts makes sense too. Thanks for contributing to my education! If I posted this at some other BB, it would have been a new reason to make fun of the ignorant poster. 50 replies later, no one would have bothered to answer the question, except in the most derogatory and insulting manner possible. So--I appreciate the help! Very much.

 

[Middleman]

Light, great information.

Maybe you can clarify some other phasing type questions.....

When I am working on multiple tracks after about the 10th track, I start to hear phasing or maybe its frequency conflict, I am not sure. Things just start to sound, not as defined, for lack of a better phrase. Is this the result of too many EQs and compression on various tracks? Do poorly written or perhaps too many plugs tend to build up kind of a digital distortion?

Perhaps this a function of the AD/DA conversions being overloaded and it would improve with a more high end sound card. Or, is this the result of just digital recording in general, all those 1s and 0s being pushed through software, plugins and converters?

Any thoughts would be appreciated.