Can someone Explain Phasing problems to me?

[JoeyPazera]

I would like to get lay mans terms on phasing issues.

if you could go over common problems also.

People say i have phasing issues in my guitar recordings. help on that would be nice also please.



thanks in advance,
-Joey

 

[kubeek]

In simple: when a signal is mixed with its copy, but the copy is a little delayed the "phasing" or "comb filtering" happens. It creates a filter which attenuates multiples of some basic frequency.

Phasing usually happens when you mike an instrument with more than one mike and have bad mike1-inst and mike2-inst distances ratio, or when you have too much leakage into other microphones like overheads.

 

[kessel]

http://en.wikipedia.org/wiki/Phase_cancellation

 

[bennychico11]

https://homerecording.com/bbs/showthread.php?t=200512&page=2&pp=25

read over my second post on this page...i have some audio and image samples (provided they are still there, it was posted awhile back).
ignore the first page unless you REALLY want to dive into it.
but hopefully that second page helps you.

 

[Flangerhans]

It can be very simple, or very complex, depending on what your problem is. I'll give you my uncomplicated explanation here, and you can work from there.
A sine wave is the beginning.All alternating signals, like musical tones, can be expressed as a sine wave. It goes, in a certain amount of time referred to as frequency, from it's highest positive value to it's lowest negative value. This range is called amplitude. In between these two extremes is a point at which the measurement of the wave is zero. Should you take this sine wave and change it's positive values to negative, and vise versa, you have just changed the phase of that wave by 180 degrees.
When you take two waves and combine them, they form a new sine wave thats amplitude is the sum of both waves at any given point. When these two waves are offset and combined, the sine wave formed may have peaks and valleys that cause the new wave to sound different, which can be a good or a bad thing, depending upon what you are trying to do. If you offset two waves by 180 degrees, they should cancel each other out completely, but they actually don't, due to reasons beyond my understanding.
When someone says that you are having phase problems, they usually mean that you are cancelling some parts of your signals by combining them out of phase in some way. This can be through use of delay, through signals that are not of the same phase, or by using electronics that cause one of your signals to be slowed down as it goes to print. One signal cannot be heard as out of phase, it takes a combination of two or more.
This is a very complicated issue in truth, and I am just giving you the basics as I understand them. Should I be wrong in any of this, hopefully one of the very bright and understanding folks here will correct me. You can literally spend months learning about the finer points of phase cancellation, and those months would be very well spent if you plan on doing any recording. Hope this helps!

 

[FALKEN]

question....

suppose an example, you have 4 tracks. drums, bass, guitar, vocals. and suppose they are each recorded with 1 mic, in separate rooms, on separate days. So the mics are not phase-cancelling each other. then suppose you have no delay or other effects. Now, there is one obvious place phase problems can come from, and that is the room itself that the mic is in, waves bouncing off walls and stuff and cancelling out at the location of the mic capsule. for the sake of argument, lets negate that too.

can mixing these 4 completely independent signals together cause phase problems?

 

[Flangerhans]

Well, you've eliminated a number of causes, yes. From what I understand, even the signal path electronics can come into play, although I've not encountered it.. I'm no phase expert, just a bunch of issues have come up in my stuff that I had to dope out the hard way.
One thing to bring up. Phase is a property of sound waves as well as the electrical signal that represents them. F'rinstance, if your sound is reaching two different mics at differing times, this can cause phase troubles when they are mixed. This has nothing to do with the electronics, just with the fact that sound does not move through air instantly.
If there is anyone reading that really knows this stuff, I am always interested in learning more, I am sure that there are whole books about this.

EDIT: I just read the thread referred to above by Bennychico11, and the thread that that one points to as well. These guys know waaaay more than me. In particular, Harvey Gerst gives a great explanation with just a little bit of math.

 

[XLR]

People say i have phasing issues in my guitar recordings.

Perhaps describe your miking setup, processing and how you mix the tracks.

 

[JoeyPazera]

Perhaps describe your miking setup, processing and how you mix the tracks.

57 about 1 inch from grill, a condenser bout 1 foot back.

 

[XLR]

57 about 1 inch from grill, a condenser bout 1 foot back.

I'm assuming you record each to a separate track. Do you time-align the tracks after recording them?

 

[Bulls Hit]

57 about 1 inch from grill, a condenser bout 1 foot back.

Sound travels at around 1100 feet per second, so it will take about a millisecond longer for the guitar sound to reach the condensor.

As Timothy alludes to, you can compensate for this by dragging the condensor track forward about a millisecond relative to the 57 track

 

[89gtsleeper]

Sound travels at around 1100 feet per second, so it will take about a millisecond longer for the guitar sound to reach the condensor.

As Timothy alludes to, you can compensate for this by dragging the condensor track forward about a millisecond relative to the 57 track

That is true, but I don't really think 1 millisecond is going to cause a serious phase problem that anybody but those with the most trained ears could catch. And even then, I really don't think they would notice. Technically though, for the sec of being a perctionist, sound in optimal conditions moves at 1130 feet per second, so you could align the tracks after recording.

Another thing you could try, is recording something with just the 57 on the cab, then do it again using the dual mic setup, and see if there is a difference in phase there??? If so, you can prove the micing is what is causing it.

 

[89gtsleeper]

going a bit more in depth with that same concept of dual micing, and the speed of sound... let's factor in on eother possibility... your mics are a foot apart, so the sound come from the speakers hits mic one immediately, hits mic two one millisecond there after, but let's say the sound the hits a wall 10 feet away, and bounces back through both mics again... now on top of those first two, it bounces back to mic 2 at 19ms, then to the 57 at 20ms.... now you have four waves hitting at different times, and the 20 ms apart could be a real problem.

 

[89gtsleeper]

and hate to say it, but that's where we could shift this whole topic back into the whole diffusor/absorber thread... yikes

 

[Bobby Darko]

okay, but that's fine. Room treatment is very important, even for us, homerecording people. I curiuous about cheap solutions. I've seen the expensive rubber/foam things, but is there a budget solution for homerecordists?

If there's already a thread, I'm sorry

I was thinking of putting some thick fabric on some wooden planks and place them at speaker hight, opposite to the amp. Could it work?

 

[bennychico11]

okay, but that's fine. Room treatment is very important, even for us, homerecording people. I curiuous about cheap solutions. I've seen the expensive rubber/foam things, but is there a budget solution for homerecordists?

If there's already a thread, I'm sorry

I was thinking of putting some thick fabric on some wooden planks and place them at speaker hight, opposite to the amp. Could it work?

there's a WHOLE section called Studio Building on the forum....should keep you busy reading for awhile.


also guys, don't confuse phase relationships as being ALWAYS a problem. Phase is a natural occurence that happens all around us. Just because a sound bounces off a wall and hits the microphone at a later time, doesn't mean it's going to create a phase problem. In fact, phase relationships between two microphones or two signals arriving late to a microphone can actually enhance the sound. Much how doubling a guitar part or recording two different vocalists singing the same thing can make a part have a different tone.
You just need to use your ears. Frequencies cancel and add all the time in your recordings, but it's when you start second guessing the sound you're recording is when you should get your first clue that there is an actual problem going on.

 

[boingoman]

That is true, but I don't really think 1 millisecond is going to cause a serious phase problem that anybody but those with the most trained ears could catch. And even then, I really don't think they would notice. Technically though, for the sec of being a perctionist, sound in optimal conditions moves at 1130 feet per second, so you could align the tracks after recording.

1 millisecond= 1 foot = 1/2 wavelength of about 600Hz

This is the frequency that will be most affected, followed by it's harmonics. So having two mics one foot apart would definitely be easy to hear. Whether you like it or not is another question.

 

[XLR]

...I don't really think 1 millisecond is going to cause a serious phase problem

A tenth that much will make a huge difference. Try it for yourself: set up a matched pair of mikes in XY config 2 ft from an ac gtr. Make sure that the capsules are exactly the same distance from the source. Record a few seconds of playing, going to separate tracks. Listen back first with the tracks hard panned, then with them summed. No phase problems when summed - excellent mono compatibility. Then move one of the mikes a half inch further away and record again. It'll sound fine when listening with the tracks hard panned L and R. But when you sum them you'll hear the comb filtering. It goes out of focus, or worse.

You can do the same kind of test just by sliding waveforms around, using tracks from two coincident mikes or just copying and pasting a mono track, in a multitrack app. Move one waveform just a tenth of a millisecond and you can hear the phase problems when you sum them. No trained ear needed.

 

[mixsit]

1 millisecond= 1 foot = 1/2 wavelength of about 600Hz

This is the frequency that will be most affected, followed by it's harmonics. So having two mics one foot apart would definitely be easy to hear. Whether you like it or not is another question.

Another factor is relative volume of the two effects the depth of the combing. Even at a foot, with an equal mix, that's a whole series of deep holes and peaks from the mids on up.