Can someone explain phase to me?

Phase is the start of the wave cycle of a sound.  Two mics and the distance from the source between them can lead to the wave starting at different times for spaced mics.  The delay can't be heard as such, but the phase cycle starting slightly off can cause cancellation of certain frequencies.

Not surprisingly, it sounds like a phaser - or a weak one for the most part.  Some frequencies wash out or reinforced - an out of sync phase sounds hollow usually.  Hard to explain but, like porno, when you hear it you know it.

How to fix - the first thing to do is flip the phase switch on the board/preamp/etc.  That flips the cycle 180 degrees, which is usually too much for small distances.  Try it first.  Next move the mics.  Usually it isn't moving the stand or arm, but, pointing the mics differently a bit.  Two mics on one source will always have a phase differential.  The trick is to match up the phase so you don't hear it.

Once you've recorded a phase problem you have to slip or increment one track.  Use your ear or if you find the start of a hit you may be able to line it up by eye, too.  But we are talking about very small changes unless you are off by feet.  One millisecond = one foot, more or less.

@

One millisecond = one foot, more or less.

and 1 millisecond equates to 1KHz, ie roughly right down the middle of the important frequencies for a guitar.  Moving a mic just 2 or 3 inches relative to another will thow all the major guitar frequencies into phase issues..

I have recorded lots of guitar tracks with two mics ... I'll. Have to practice listening for it and checking it I think Or am I making a bigger deal out of it then it needs to be ?

The important thing to remember here is that music is art,  if it sounds the way you want it to sound then it is right, regardless of any technical issues that others may point out.
 
If you're using two mics and are fighting to get a sound you like,  it may be because of phase issues. 
You can of course deliberately shift a mic to induce phase issues to get a specific sound...
 
 
Yes, there's a phase button on the X1 inputs, but it is NOT intended to fix bad mic placement.
Where you have a mic above and below a snare for example, one of them (usually the lower) will need phase reversing.  That's what the button is for.

If you use one mic on a sound source, phase is not so much of an issue.

Think of phase in a mathematical sense....There are  positive and negative peaks on every wave.....with zero being a center point. 

 If 2 POSITIVE wave peaks arrive at the same time...they add together and the result is twice what either is by themselves.  +1 + +1=+2  These are said to be in phase and they add to each other..... room and other sorts of resonances are the result of this occurring.

If 2 waves arrive at the same time BUT one is peaking positive and one is peaking negative, they still add..... but the result is zero  +1 + -1=0  These are said to be 180 degrees out of phase and they cancel each other out. Room nulls, lack of certain frequencies in a room are the result of this occurring. 

You can demonstrate this on your DAW by taking any given audio track and cloning it. Set both track volumes to 0db and mute one while playing the other. Now un-mute them both and play them together. You should hear a slight but noticeable volume increase with both playing. Now.... use the phase button in the track and play them both again together..... there should be absolute silence as the two waves are now complete and exact opposites and are canceling each other perfectly.  Any variation between the two will result in some sort of sound.

These are the two extremes.... it gets much more interesting and unpredictable when the wave are somewhere in between and are out of phase to one degree or another.  At a given frequency, the wave will be something like   +.50 + -1.25= -.75  (hitting the two mics out of phase)   This will be changing according to the frequency...since the wave length from one frequency to the next will be different. 

So while the speed of the sound will remain the same, (about 1 foot per millisecond)  the wave length is the variable as is the distance to the mic(s).... and when you add the waves together in the algebraic fashion you get changing phase issues. Certain frequencies get canceled and others get boosted. This is one of the problems you face using two mics. As the frequency of the note played changes, as on a guitar neck, the phase relationship hitting the 2 mics is changing constantly and you WILL have some degree of frequency phase cancellation. The trick is to find the best compromise position for the 2 mics or use one mic and not worry... but then you don't have the advantages of better sound with the 2 mics..... it's a trade off either way. 

There are charts and web sites that you can also google to understand this better in a visual manner.  

http://www.indiana.edu/~emusic/acoustics/phase.htm

http://www.soundonsound.c...s/phasedemystified.htm

We refer every now and then to "comb filtering" in the music and that is generally the result of the varying phases between the frequencies. This is an audible phenomena and is undesirable. Great efforts are expended to avoid it.  

dan le


Bill:
If phase is what you talked about, then how about when you try to thicken a vocal, and then the advice is to clone 2 tracks, slide one track a little ahead and the other track a little late, wouldn't that cause phasing big time.  And this advice is given by a lot of people including Scott at Digifreq I think, on this forum.
 
dan le
 

This is technique for enhancing a part.
 
The easiest way I can think of is the relationship with the bass drum and the bass. Everyone knows how difficult it can be for both instruments to be heard at the same time without one masking (phasing with) the other. There are different methods to achieve this. IMO, the best method is using the EQ and making sure there is room in the frequency spectrum for both.
 
That's basicly what it comes down too. making sure frequecies are not masking (phasing) each other.
 
Try this. Take a guitar track and clone it. on the cloned track press the phase button. You'll notice that played together there is no sound. They are exactly phased and cancel each other out. Now on the original track, create high peaks around 440hz, 880hz and 1760mz. Now group those three frequency knobs together. Lastly, play the track while moving one of the knobs up and down (moving the frequency) and listen. It's a nice way to create a phaser sound. You can adjust the frequencies to taste but you'll get the idea.
 
HTH.
 
Great thread and a nice read.