Phase question

[jonmmartin]

I have 2 unmatched small condenser mics. For recording in stereo, is it better to use the phase reverse button on the mic pre or to move the mics using the 3 to 1 rule when phase issues exist. The question is...does engaging the phase reverse button degrade the sound.
Also, can someone explain the technique for checking phase problems when using multiple mics on one source.
Thanks for the help.

 

[c7sus]

Phase issues result from sound waves reaching the mics at different times; that is to say if the sound wave reached both capsules simultaneously you would have perfectly in-phase stereo recordings.

But it's not physically possible to make that happen. Soundwaves are diffuse, rooms have their own reflections and "sound". Two mic capsules cannot occupy the same physical point in space.

The phase-reverse function inverts the waveform 180. Essentially makes it the mirror image of itself.

If our two perfectly recorded waveforms were put side-by-side and we phase-inverted one of them the two waveforms cancel each other out.

Play those tracks back at the same time and you should hear NO SOUND if both tracks are at the same volume.

The 3-1 rule applies to keep phase issues from getting too far out of hand. Frankly, the math behind the 3-1 rule is over my head. It doesn't make a lot of sense to me that putting one mic 6" from the source and the other mic 18" from the source compensates a low-E sinewave that is 30 FEET long!

 

[Farview]

The 3 to 1 rule is for 2 mics on 2 sources. It has nothing to do with micing one source with multiple mics.

 

[c7sus]

I am afraid you are mistaken. The 3-1 rule is most certainly about using multiple mics on a single source.

And the 3-1 doesn't only apply to the lateral plane in front of the source. It also applies to depth of field. So if you put the first mic 2 feet in front of a guitar the second mic would want to be 6 feet in front of the guitar for proper phase alignment. Like I said, the math is over my head. But this is accepted practice.

http://humbuckermusic.com/acguitrectec.html


With this approach -- as with any miking technique that uses two or more mics that are spaced apart from one another -- always be sure to follow the "3-to-1 rule." According to this rule, the distance between two mics should be at least three times the distance between each mic and the sound source. This keeps phase cancellations to a minimum, resulting in a smoother sound that also translates well to mono. So, for instance, if you've got each mic seven inches from the guitar, the 3-to-1 rule mandates that you spread the two mics at least 21 inches apart from each other. (One of a few exceptions to the 3-to-1 rule is with the X-Y technique, as described below.)

 

[Farview]

That is a myth. The 3 to 1 rule is for 2 mics on 2 sources in the same space. Like when you are recording a band in a room. It cuts down on both bleed and phase.

You will always get phase cancellation at some frequency when using 2 mics on the same source. The smaller the distance between the mics, the higher the cancelled frequency. It also doesn't have anything to do with spaced pairs. Think about it, if you have spaced pair overheads that are 8 feet away from the snare drum, they would have to be 24 feet apart to use the 3 to 1 rule. It's ridiculous.

 

[boingoman]

I am afraid you are mistaken. The 3-1 rule is most certainly about using multiple mics on a single source.

So if my stereo mics are 3 feet above my drums, they should be 9 feet apart? You may want to rethink that.