Is it true that omnis dont have phase problems?

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r0t4ry
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Is it true that omnis dont have phase problems?

Post by r0t4ry » Mon May 05, 2008 1:08 pm

Just like the title says. Last night 2 SDC's (Cardoid) in spaced pair on an acoustic and it sounded much more out of phase then 2 Omni's in same place. Ive heard that omni's have no phase issues but I wanna know what you guys think.

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Re: Is it true that omnis dont have phase problems?

Post by Nick Sevilla » Mon May 05, 2008 1:22 pm

r0t4ry wrote:Re: Is it true that omnis dont have phase problems?

Just like the title says. Last night 2 SDC's (Cardoid) in spaced pair on an acoustic and it sounded much more out of phase then 2 Omni's in same place. Ive heard that omni's have no phase issues but I wanna know what you guys think.
Hi,

Phase issues only come into play when you start recording with more than ONE microphone.

These issues are directly related to the distances both between the two microphones and the sound source.

Since two microphones cannot occupy the same exact space, the sound travelling through the air MUST hit the two diafragms at different times. There is simply no way around this.

However, there have been several techniques developed to MINIMIZE the phase issue, and you can find those by doing a search on Dr. Blumlein, for example. Or on this forum, as well.

So, to answer your question as to whether using two OMNI microphones not having phase issues, this is FALSE.

If you are using ANY ONE microphone, you will not have phase issues. As soon as you use TWO or MORE, phase becomes an issue that has to be addressed.

Cheers
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Post by Rodgre » Mon May 05, 2008 1:41 pm

While the above post is a good explanation of how and why phase issues occur, in the recording environment, you will have less phase issues with omni mics because the sound that they are picking up is coming to it from all directions: including a good deal of reflected (ambient) sound. Why does this not sound bad to me when I use omnis as overheads? I feel that the tighter the pattern of a mic (Cardioid), the more acute the phase/time alignment is an issue in relation to another nearby mic.

You may still find that inverting the polarity (or the moving) of an omni mic will will have tonal differences, and there may still be phase issues with other mics (for example, I use Stapes Omnis as drum overheads frequently, and beside the fact that due to a minor design flaw of the first batch, they are inverted polarity out of the chute, I still flip the polarity to find where the mic sounds best with my kick, snare and tom mics).

I hope this helps. Use your ears. Phase issues on a micro/oscillo-scopic level are what makes stereo imaging, and interesting tonal possibilities so it's both good and bad.

Roger

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Post by ashcat_lt » Mon May 05, 2008 2:07 pm

Of course, a directional microphone's frequency response changes as the source moves off-axis. This alone may account for some of what you were hearing.

On top of that, though, and unless I'm completely mistaken, a directional mic's phase response also changes off-axis. I'd be willing to bet that this is the major cause of your experience here.

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Re: Is it true that omnis dont have phase problems?

Post by r0t4ry » Mon May 05, 2008 2:16 pm

i ofcourse know what phase is and why it occurs. what makes it lessened on omnis is what i dont know, or if it was fact for reasons beyond my understanding. i wonder if professor has some good explanation.

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Re: Is it true that omnis dont have phase problems?

Post by chris harris » Mon May 05, 2008 2:31 pm

r0t4ry wrote:i ofcourse know what phase is and why it occurs. what makes it lessened on omnis is what i dont know, or if it was fact for reasons beyond my understanding. i wonder if professor has some good explanation.
the omnis have a different pattern and frequency response. it's not that there are necessarily less phase issues when using a pair of omnis. it's just that the phase relationship will be different because of the differing pattern and frequency response. I don't think that you can say that anytime you replace a pair of cardioid mics with omnis that you'll have less phase issues. You'll just have different phase issues. But, there are definitely plenty of phase issues to be had with omnis.

sounds like you just happened to have fewer phase issues in this one particular spot, in this one particular application, and you're trying to credit that omni pattern with saving the day. You didn't have less phase issues because omnis have less than cardioid. You had less phase issues because your placement was more phase coherent with those particular omnis on that source, than the cardioids were.

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Re: Is it true that omnis dont have phase problems?

Post by Nick Sevilla » Mon May 05, 2008 3:32 pm

subatomic pieces wrote:
r0t4ry wrote:i ofcourse know what phase is and why it occurs. what makes it lessened on omnis is what i dont know, or if it was fact for reasons beyond my understanding. i wonder if professor has some good explanation.
the omnis have a different pattern and frequency response. it's not that there are necessarily less phase issues when using a pair of omnis. it's just that the phase relationship will be different because of the differing pattern and frequency response. I don't think that you can say that anytime you replace a pair of cardioid mics with omnis that you'll have less phase issues. You'll just have different phase issues. But, there are definitely plenty of phase issues to be had with omnis.

sounds like you just happened to have fewer phase issues in this one particular spot, in this one particular application, and you're trying to credit that omni pattern with saving the day. You didn't have less phase issues because omnis have less than cardioid. You had less phase issues because your placement was more phase coherent with those particular omnis on that source, than the cardioids were.
+1
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Post by locosoundman » Mon May 05, 2008 5:04 pm

Just curious:

How did you have the mic's panned?

"Phase problems" could mean "phase cancellation" in mono or too much de-correlation between the left and right channels (an extreme case of this could be caused by reversed polarity on one channel).

I just want to figure out which one we are talking about here.
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Re: Is it true that omnis dont have phase problems?

Post by cgarges » Mon May 05, 2008 7:29 pm

noeqplease wrote:If you are using ANY ONE microphone, you will not have phase issues.
Actually, you can have phase issues with one microphone on several levels, obvious or minute as they may be. The most obvious one would be recording with a microphone close to a reflective surface, where the microphone gets both direct and reflected sounds at slightly different arrival times. A prime example of this would be recording a vocalist with a music stand angles to reflect directly into the microphone.

And in all honesty, angling a microphone in relation to a sound source changes the sound of the microphone because a phase error is introduced across the diaphragm of the mic. Subtle, but true. Not what we classically think of in terms of phase issues, but existent nonetheless.

Chris Garges
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Re: Is it true that omnis dont have phase problems?

Post by mjau » Mon May 05, 2008 7:33 pm

cgarges wrote:And in all honesty, angling a microphone in relation to a sound source changes the sound of the microphone because a phase error is introduced across the diaphragm of the mic.
Wouldn't this be the case even if the mic were not angled, i.e., won't some soundwaves hit parts of the mic capsule at a less than/greater than 90 degree angle no matter how it's positioned?
Totally splitting hairs, but kinda fun to think about.

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Post by cgarges » Mon May 05, 2008 7:47 pm

Cosmic.

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Re: Is it true that omnis dont have phase problems?

Post by ashcat_lt » Mon May 05, 2008 9:38 pm

noeqplease wrote:
subatomic pieces wrote:
r0t4ry wrote:...
...
+1
+1 (I'm pretty sure that's what I said)

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Re: Is it true that omnis dont have phase problems?

Post by Nick Sevilla » Tue May 06, 2008 7:51 am

cgarges wrote:
noeqplease wrote:If you are using ANY ONE microphone, you will not have phase issues.
Actually, you can have phase issues with one microphone on several levels, obvious or minute as they may be. The most obvious one would be recording with a microphone close to a reflective surface, where the microphone gets both direct and reflected sounds at slightly different arrival times. A prime example of this would be recording a vocalist with a music stand angles to reflect directly into the microphone.

And in all honesty, angling a microphone in relation to a sound source changes the sound of the microphone because a phase error is introduced across the diaphragm of the mic. Subtle, but true. Not what we classically think of in terms of phase issues, but existent nonetheless.

Chris Garges
Charlotte, NC
True Chris, however I was only addressing the two microphone technique that the OP was talking about. And only that phase issue.

I think if the OP started to really look at what goes on when recording sounds, from more than the mic perspective, he'll freak out. Too much information.

But it is a good info for him to have nonetheless. Maybe next time the Op will spend more time in the care of placing the mics, and have even better results.

And, since we don't get to hear any examples...well...all of this is rather one sided opinions anyways.

Maybe we can get a sound sample from the OP, and "see" what he did.

Cheers
Howling at the neighbors. Hoping they have more mic cables.

r0t4ry
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Post by r0t4ry » Tue May 06, 2008 8:22 am

lol it was 1 question that no one is truely explaining just guessing at. so dont guess at it. i know how phase differences work. quit trying to teach me about everything i already obviously know, im not a newb over here going DURRR HowW DoEs i RecErd tEh MuSIC. the question was, do you think omnis have phase issues or not, not "can u explain to me what phase is and how it works".

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Post by MoreSpaceEcho » Tue May 06, 2008 9:46 am

aaaaaaaaaaaaaaaand you're welcome for the help.

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