How to know when your mic is out of phase...

[wx3]

Hmm... I was recording my guitar amp with two mics....

A 57 close miced and a Studio Projects B1 at about 4 feet away each recorded to a seperate track.

What I was wondering is... How can I tell if my mics are out of phase? I inverted the phase switch, on the B1 track, in Sonar and it made it sound more mellow. It wasnt better or worse, just different.

I'm pretty sure I understand what phase is, but could someone re-cap me please? Also how do you know if your two mics are out of phase?

Thanks,
Chris

 

[jrosenstein]

phase is basically the timing of the peaks in a wave. if you have two 60hz tones, and they are totally out of phase, that means that when one wave is at its peak, the other is at its minimum. thus when they're added, they totally cancel out and you get complete silence. if two signals are only partially out of phase, the combined signal will just have lower volume.

differences in phase often occur because of mic positioning. a sound wave is not instantaneous. it takes some time to reach the mics, so mics placed around the room will receive the signal at slightly different times. also, if two mics are facing opposite directions in the same location, they will have reversed polarity, which is more like flipping the wave vertically, and knocking ALL frequencies "out of phase."

low frequencies have much more of an opportunity to be out of phase than high frequencies, due to their longer wavelengths. if you have more than one mic in the room, SOME frequencies will be at least a little bit out of phase between the mics, but it is most noticeable when the low frequencies are cancelling each other out.

for your purposes, whichever way has more bass is probably the one that would be considered "in phase." on your computer, if you zoom in on the 2 waveforms side by side, you can see whether their peaks occur at the same time. it's easier to see if you try it out with a constant tone, from a tuner or something.