Polarity

assuming this is a balanced xlr mic, you would need a cable, adaptor, or feature on a mixer/preamp/etc. that reverses the connections to pins 2 and 3 on the xlr connector.
 
an audio signal is represented electrically with a voltage difference between two conductors. if you reverse the polarity -- swap which conductor is positive and which is negative -- the measured voltage is essentially multiplied by -1. If you think about it as a sine wave on a graph, the whole thing is flipped across the x-axis.

if you were to take a signal, reverse its polarity, and add it to the original, the entire thing would cancel out and go to zero. this makes sense -- if at any point the original signal has a value of Y, the polarity-reversed signal has a value of -Y. Add them and you get zero.

A very similar effect can occur from time delays (differences in phase). If you delay a sine wave by 1/2 its period and add it to the original, you will also zero out the signal. The wave oscillates from positive to negative. Shift one wave so that the negatives line up with the positives of the original, and it looks just like its polarity was reversed.

Since no two microphones can be at *exactly* the same place in a room, they will receive a sound at slightly different times. Sometimes this delay can cause different frequencies to be out of phase and cancel each other out. Low frequencies, with longer wavelengths, are particularly prone to phase issues. If you find yourself in this situation, and you reverse the polarity of one of the microphones, the two signals will now no longer cancel out. Problem solved.
 
Thanks, Jrosenstein. Very informative. If I'm recording in stereo, would you recommend reversing the polarity of one of the mics just to make sure there is no phase problem? And I ask because I'm not so sure I'll know if I'm losing full sound do to phase problems...
 
just because there is more than one mic in the room does not *necessarily* mean you'll have phase problems. even if you do, they can often be fixed by mic placement instead of flipping polarity. it's not just an issue of IN phase and OUT of phase ... you can be anywhere in between as well. this is what gives stereo recording its "space" in the first place. if you have two mics next to each other, chances are that flipping one of the polarities will CAUSE these phasing problems that we're discussing. unless your mics are facing in opposite directions, or are farther from each other than they are from the sound source, you probably won't want to reverse polarity on one.

so the answer is no, don't always flip one of the polarities. go ahead and flip it temporarily, but compare what it sounds like each way, and pick the one that's best. (typically the one with more bass would be considered to be the one that's "in phase")
 
Sorry for my dumbass questions, but

1) what is reverse polarity and why is this good?
2) How does that affect the sound of the vocals?
3) Is the "reverse phase" function on my ART tube MP the same as reverse polarity?

Please have mercy on this newbie.


KF
 
Knopfler Fan said:

1) what is reverse polarity and why is this good?
Click to expand...
see my posts on this thread, i think i explained it, but if you have more specific questions i could try to rephrase myself or expand on what i said.


2) How does that affect the sound of the vocals?
Click to expand...
It doesn't. it would only effect how the vocals combine with other signals.


3) Is the "reverse phase" function on my ART tube MP the same as reverse polarity?
Click to expand...

Yes



Please have mercy on this newbie.


KF
Click to expand...
 
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