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When to flip polarity?
Old 2 weeks ago
  #1
Gear Maniac
 

When to flip polarity?

Hi there. I am recording a cajon and I have a SM57 on the soundhole at the back with a Oktavamk012 cardioid mic on the front panel. The microphones are about 50cm apart facing each other with the cajon in the middle. so my question is, should you flip the polarity on one of the tracks or is it just up to taste and what "sounds better"? if I flip one it does sound a bit better to my ears but I wouldn't say that I need to flip it. I mean, it sounds alright either way. Can someone please explain if this should be done and why?
Old 2 weeks ago
  #2
I usually flip polarity when i have a phase issue and its audible. But i always try to move the mic to solve the phase issue before i flip the phase.

Also, you can always flip the phase after its recorded in your DAW after its been recorded.
Old 2 weeks ago
  #3
Gear Maniac
 

Quote:
Originally Posted by CJ Mastering View Post
I usually flip polarity when i have a phase issue and its audible. But i always try to move the mic to solve the phase issue before i flip the phase.

Also, you can always flip the phase after its recorded in your DAW after its been recorded.
Thanks. What do you hear when you flip the polarity. The two recordings sound fine either way so not sure what you should be looking for?
Old 2 weeks ago
  #4
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Owen L T's Avatar
Are you recording to a DAW, where you can see the waveforms? Because what you're looking for, literally, is the case where one track is showing a peak, where the other is showing a valley. On a snare, this can happen with top and bottom mics, and can be a genuine polarity issue. Or, reagrding overheads and directs, it can be the case that the time difference can result in phase issues - where flipping the polarity migh improve the phase situation, though in neither position are the tracks either perfectly in phase, or 180 degrees out of phase.

In botb case it's what happens when the same sound soirce is captured by different mics. All tracks will have the same shape, but timing (or polarity; differences mean that these waves are rarely in perfect alignment. The closer you are to a situation where one peaks where the other troughs, the more they are beginning to cancel each other out in some areas of the spectrum. The combined sound won't be obviously quieter, but can begin to lack body.

If you don't notice a difference, then it likely means the tracks are neither in nor out of phase, but somewhere in between. Keep one mic where it is, and move the other closer/further by a few inches, and see if you hear a difference. Or use one of the in-between phase plugins to see/hear if there's any appreciable difference.
Old 2 weeks ago
  #5
Gear Maniac
 

Quote:
Originally Posted by Owen L T View Post
Are you recording to a DAW, where you can see the waveforms? Because what you're looking for, literally, is the case where one track is showing a peak, where the other is showing a valley. On a snare, this can happen with top and bottom mics, and can be a genuine polarity issue. Or, reagrding overheads and directs, it can be the case that the time difference can result in phase issues - where flipping the polarity migh improve the phase situation, though in neither position are the tracks either perfectly in phase, or 180 degrees out of phase.

In botb case it's what happens when the same sound soirce is captured by different mics. All tracks will have the same shape, but timing (or polarity; differences mean that these waves are rarely in perfect alignment. The closer you are to a situation where one peaks where the other troughs, the more they are beginning to cancel each other out in some areas of the spectrum. The combined sound won't be obviously quieter, but can begin to lack body.

If you don't notice a difference, then it likely means the tracks are neither in nor out of phase, but somewhere in between. Keep one mic where it is, and move the other closer/further by a few inches, and see if you hear a difference. Or use one of the in-between phase plugins to see/hear if there's any appreciable difference.
Yes I am recording into a DAW. I can see the waveform so I will look for what you explained and see if there is a genuine polarity issue.

Can this also happen when recording a guitar with two microphones? I may have to learn how to do this soon and I am glad to be learning about this now. I play a lot of acoustic guitar and many miking techniques involve two microphones for a stereo recording. I have read that this can produce polarity issues. In this case could the issue also be resolved by moving one of the microphones?

Another video I watched on you tube yesterday speaks about how high pass filters change the polarity of a recording and that this can also produce polarity problems. The engineer recommended to always group the two recordings to a bus before using an EQ. Is this correct?
Old 2 weeks ago
  #6
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Fay Smearing's Avatar
 

Quote:
Originally Posted by camomiletea View Post

Another video I watched on you tube yesterday speaks about how high pass filters change the polarity of a recording and that this can also produce polarity problems. The engineer recommended to always group the two recordings to a bus before using an EQ. Is this correct?

You (or the person in the video you watched) seem to be using the term polarity where it should be phase, as in: 'a high pass filter causes phase shift' - it doesn't shift the whole audio range 180 degrees like swapping polarity does.

Flipping the polarity effectively gives 180 degrees "shift" at all frequencies.

The amount of phase shift caused by delay is frequency dependent because of wavelength changing with frequency (and thus you get 'comb filtering').

It's a simple but important distinction to understand with sound.
Old 2 weeks ago
  #7
Gear Guru
 

when I am using two or more mics on a single source, I will check the polarity as a matter of course. Just flip it back and forth. If there is an issue, one version should sound significantly better than the other. You know you have a problem when you gradually fade-in that second mic and the result sounds "lesser".

Quote:
should you flip the polarity on one of the tracks
while two mics facing towards each other is a greater risk of cancellation, there are other factors - such as the distances, that may come into play. Sometimes that snare-under mic does not need to be flipped. I even have a few vintage mics that are reversed-wired! And on the other hand, two mics facing in the same direction might be "out". Miked cabinet plus DI is another place where this could happen.

I would say, always check, never assume.

Quote:
or is it just up to taste and what "sounds better"?
Comb-filtering is caused by cancellations at different frequencies. If you flip one of the signals, you may indeed fix one frequency and put another out. However many times it is pretty obvious that one version sounds more "solid" than the other. I usually judge by what is happening in the lower fundamentals of the sound. If it is not obvious, then I don't worry about it.

Last edited by joeq; 2 weeks ago at 08:33 PM..
Old 2 weeks ago
  #8
Great advice already. You asked what to listen for. Cut to the chase, it's usually the lowend you should pay most attention to. If one combination yields a more solid lowend punch, that's the one to go with.
You also asked about multiple mics recording a guitar. You definitely want those to get in good phase relationship. Two easy tricks: Set up the mics, record and make a clear transient sound with the guitar, like hitting the muted strings. Stop recording and check the waveforms. You want all mics to pick up at the same time and in the same direction. Move them until that's the case. The second one is even easier: if you're recording an amp, set up the first mic so that it sounds good. Now bring in the second and flip the phase. While listening to the combination of this and the first mic, move it until the sound almost disappears. Flip the phase back and voila.
Old 2 weeks ago
  #9
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BIG BUDDHA's Avatar
Quote:
Originally Posted by JSchlomo View Post
Great advice already. You asked what to listen for. Cut to the chase, it's usually the lowend you should pay most attention to. If one combination yields a more solid lowend punch, that's the one to go with.
.
there is the answer for you.

Buddha
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