checking phase

[freestyle tromb]

i have a few questions about phase issues.
so i just bought a pair of peluso small-diaphragm omnis, and i used them to record a string quartet on sunday. i was really pleased with the sound right off the bat, but then i realized i'd better check to make sure there's no comb filtering, phase cancellation, etc. going on. so i hit the mono button, and sure enough, the tone changes completely. also, i had a multi-meter going in logic, and the "correlation" meter was moving around quite a bit, somewhere between "0" and "+1." i honestly don't really know what the correlation meter means, but i think it was telling me that the two mics weren't quite in phase.

anyway, i just had the omnis in an AB pair; at first, i had them slightly pointed outwards, sort of leaning towards ortf. then i brought them back in so they were pointing straight forward.

i guess the question is, how do you check for phase issues? and what issues can come up? and what can you DO about them- just move the mics around and hope for the best? if possible, answers that relate specifically to a pair of omnis would be good, but i have a lot to learn about all that stuff.

i realize any near-coincident technique will not lend itself to everything being perfectly in-phase; i guess that's one advantage of blumlein and x-y. but i really do like the sound of omnis.

anyway, thanks! (i'm going to post some samples later this week of the recording.)

[AudioFields]

try pressing the phase button right at the beginning....ounce you here cancellation, reverse the phase back to normal, and then you know that you're okay. The more you train yourself to hear things "out of phase", the more you'll know when its right.

[freestyle tromb]

huh! not a bad idea.

i've been reading some posts about measuring distance to a bass or snare drum when recording a kit, so the overheads are the same distance from it; i wonder how i might apply that principle to recording a string quartet? or other chamber group?

[doorknocker]

Originally Posted by freestyle tromb

i guess the question is, how do you check for phase issues? and what issues can come up? and what can you DO about them- just move the mics around and hope for the best?

Little Labs IBP

It's a magic weapon if there ever was one. It'll allow you to position the mics where they sound best individually and then adjust the phase with the IBP until you get the sound you want.

The IBP might take a while to get used to. Not because of any technical issues but rather because you need to learn to trust your ears. Move the knobs till it sounds best.
It's also a fantastic DI and reamp box, if you only need the phase function though you might want the IBP Jr. that's more affordable. I got both but surely will get a third box at some point, it's highly recommended.

[Lakeside]

Originally Posted by doorknocker

Little Labs IBP

It's a magic weapon if there ever was one. It'll allow you to position the mics where they sound best individually and then adjust the phase with the IBP until you get the sound you want.

The IBP might take a while to get used to. Not because of any technical issues but rather because you need to learn to trust your ears. Move the knobs till it sounds best.
It's also a fantastic DI and reamp box, if you only need the phase function though you might want the IBP Jr. that's more affordable. I got both but surely will get a third box at some point, it's highly recommended.

Have you ever seen something like this in a digital or plug-in version? I could use one of those!

[doorknocker]

Originally Posted by Lakeside

Have you ever seen something like this in a digital or plug-in version? I could use one of those!

I don't think that it exists, though there are plenty of phase tools available. Shifting tracks might work sometimes but it's definitely not the same as using the IBP.

This might help: http://www.littlelabs.com/IBPMAN.pdf

[Jimbo]

There are, at least, two digital versions, but I'm not sure how good they are.

Do a search here. It's been covered before.

[freestyle tromb]

whoa! so THAT'S what the ibp does! that sounds like an incredibly useful box.

[Remoteness]

Originally Posted by freestyle tromb

whoa! so THAT'S what the ibp does! that sounds like an incredibly useful box.

It sure is!

[Musiclab]

Originally Posted by freestyle tromb

i have a few questions about phase issues.
so i just bought a pair of peluso small-diaphragm omnis, and i used them to record a string quartet on sunday. i was really pleased with the sound right off the bat, but then i realized i'd better check to make sure there's no comb filtering, phase cancellation, etc. going on. so i hit the mono button, and sure enough, the tone changes completely. also, i had a multi-meter going in logic, and the "correlation" meter was moving around quite a bit, somewhere between "0" and "+1." i honestly don't really know what the correlation meter means, but i think it was telling me that the two mics weren't quite in phase.

anyway, i just had the omnis in an AB pair; at first, i had them slightly pointed outwards, sort of leaning towards ortf. then i brought them back in so they were pointing straight forward.

i guess the question is, how do you check for phase issues? and what issues can come up? and what can you DO about them- just move the mics around and hope for the best? if possible, answers that relate specifically to a pair of omnis would be good, but i have a lot to learn about all that stuff.

i realize any near-coincident technique will not lend itself to everything being perfectly in-phase; i guess that's one advantage of blumlein and x-y. but i really do like the sound of omnis.

anyway, thanks! (i'm going to post some samples later this week of the recording.)

The tone will change alittle and you'll notice the image collapse from stereo to mono.
Thats why its stereo. The Phase correlation meter in logic is telling you your stereo file IS in phase. It's when the needle goes to the left and the minus numbers that you have a problem. The IBP is a wonderful tool, but I wouldn't mess with it in a live situation unless you have separation from the recording area. If you dont hear what you're doing with that box you can inflict way more harm than good.

[Remoteness]

Originally Posted by Musiclab

The tone will change alittle and you'll notice the image collapse from stereo to mono.
Thats why its stereo. The Phase correlation meter in logic is telling you your stereo file IS in phase. It's when the needle goes to the left and the minus numbers that you have a problem. The IBP is a wonderful tool, but I wouldn't mess with it in a live situation unless you have separation from the recording area. If you dont hear what you're doing with that box you can inflict way more harm than good.

Well said!

[freestyle tromb]

thank you guys!
this is all great advice. i appreciate it.