Using two mics - out of phase?

[miroslav]

...The irony is Slash actually knows how to play guitar; 98% of his "tone" comes from his fingers. You could tape a lav to his cabinet and it would sound great. 4 mics, let alone 40, is little more than a PR stunt, IMHO.

Yeah...probably was just a stunt...though it's easy to see how it becomes part of studio fact...and then breeds kopykats who don't get the joke!

But I have to say...I've read my share of magazine interviews where some well-known engineer is talking about serous multi-mic setups in order to get some "sound" on the latest CD of band XYZ...etc.

I often wonder how many of those engineers are just telling tall tales during interviews to sound "cool" or to cover their tracks...or just to yank some chains!

 

[SouthSIDE Glen]

I think some boys just really like playing with their toys. I don't think they're yanking our chains, necessarily, though sometimes I think they might - knowingly or not - be yanking their own.

That Slash, story, for example: I don't know the details, and I could be wrong, but I figure if I was one of the most famous living guitar players and I had the money and the time to play around in a big boy studio - one of the world's most expensive toy stores - with a great mic locker, I'd probably be attracted to the idea of sticking 40 mics up and seeing what kind of results they yielded, even if for nothing else than to build an encyclopedia of knowledge for myself on just what mic X does for guitar Y on amp Z.

But does one really need 40 mics to get a good sound? Hell no. Even if they did take all 40 mics and blend them together to create one big composite sound (which I seriously doubt), was that really necessary? Did it really make or break the recording? Does someone the caliber of Slash yielding the plectrum really need some super-synthesized tone in order to make a blockbuster sound or a song that millions will want to listen to? I seriously doubt it. As good as the engineer may make it sound, there comes a point when the pissing is over and you're just shaking your dick.

If you can afford it, and have the capability to do it, and get a kick out of it, then go ahead and knock yourself out, I say. But I don't think too may lessons should be derived from it as an example of how things should be or need to be done. Pros are humans too, and not everything they do is meant to be emulated as a "teaching moment".

IMHO, YMMV, LSAT, SAT, ACT, ETC.

G.

 

[mixsit]

I was always under the assumption that it was at least 3 times.

When I put a 57 up on da grill or maybe one inch off, I'll have an LDC or whatever about 3 feet back.
I think it's "at least".

The core of 3:1 is attenuation, by any means, that reduces unwanted combined out of phase affects. The minimum target' (IIRC ) is -9db? That could be as simple as separating the mics or sources, or putting a towel over a music stand.

Anywho, anything that messes with 'equal sensitivity of the two mics, 'omni vs. cardioid, relative mix levels later, or unequal source volumes in the case of 'two sources, all that distance stuff goes right out da window.

There's nothing I hate more than the 3:1 rule, because ever single person has a different definition, and almost none of them are correct. I don't know who started it or how it turned into the ugly beast that it is today, but it's one of those things that all engineers should just purge from their minds because it hasn't caused anything but confusion.

I hear ya. But I firmly believe the frustration and confusion stems from any number of situations where it's mentioned, or taught' with the focus on 'distance, but without or rather than, attenuation.
Start with attenuation (..it's the same as the depth' or wet/dry mix on our 'phase shifters for crying out loud

 

[Yonce N Mild]

I don't worry about phase. Not that I'm not aware of it, I just don't worry about it. I set my mics. I record a little. I listen back if I hear phase issues I move one of the mics and then repeat until I don't hear any issues.

 

[JFrankParnell]

I've done dual mics on accoustic guitar a few times. stick one up close to the guitar, angling and placing to taste. Then put the other mic exactly 4 feet back. (or whatever distance you like). Then i delayed the close mic by however many milliseconds it takes for sound to travel 4 feet. Worked really nice actually.

but i never tried it on amps. i just stick a 57 up in there

 

[soundchaser59]

Try flipping the second mic out of polarity.

Move the mic until it sounds HORRIBLY out of phase. Flip the polarity switch back.

Yeah good idea. Set one mic reverse phase, then move the mic around until the sound (of both mics being monitored) is completely (or as much as you can get it) cancelled out. Then flip the phase back.

3 to 1 is precise, and as stated above is for times when you want an honest stereo recording. And it also means 3 to 1 from the same source. Both mics should have the exact same relationship to the exact same source. Dont make one mic close to the edge of the speaker, for example. It's more difficult if you are using two different mics, instead of two identical mics.

 

[soundchaser59]

I don't worry about phase. Not that I'm not aware of it, I just don't worry about it. I set my mics. I record a little. I listen back if I hear phase issues I move one of the mics and then repeat until I don't hear any issues.

If you were not worried about phasing, then you wouldn't go thru that process.

Of you are going thru that process so that you dont have to worry about it.

You cant separate the two. You do that process because phasing between two mics matters.

Any other hairs we can split......

 

[soundchaser59]

But, there have been a small handful of times where the mic selection I had available to me was wanting, and I had to blend two mics to get a serviceable sound.

I suspect your "small handful of times" actually describes the home recording enthusiast's "vast majority of times."

 

[soundchaser59]

I was always under the assumption that it was at least 3 times.

When I put a 57 up on da grill or maybe one inch off, I'll have an LDC or whatever about 3 feet back.
I think it's "at least".

Let's see here....

1 inch......

3 feet......


That would be at least 36 times.....

 

[SouthSIDE Glen]

3 to 1 is precise, and as stated above is for times when you want an honest stereo recording. And it also means 3 to 1 from the same source. Both mics should have the exact same relationship to the exact same source. Dont make one mic close to the edge of the speaker, for example. It's more difficult if you are using two different mics, instead of two identical mics.

Invert the polarity on this quote so that everything is stated exactly the opposite, as if it's a quote from Bizzaro World, and you might have something close to the actual truth.

There is nothing anywhere that demonstrates that there is anything "precice" about the 3:1 ratio whatsoever.

Plus, if it had anything to to with "honest" stereo recording, then stereo configurations like X/Y and ORTF would be invalid - not to mention figure 8 mics and mic setups, Jecklin discs, M/S matricies, etc.

Even more than that, spaced stereo pairs have to be spaced proportional to the apparent angular size of the source being miked, something that if you tried to apply the the 3:1 rule to stereo miking, it wouldn't even address.

And there is no rule or premise behind any such alleged rule that states that stereo mics have to have an "identical relationship" to the source. In fact for most sources worth capturing in stereo, that's impossible. Consider stereo miking of a piano or acoustic guitar, or stereo miking of a quartet (vocal or instrumental), where it is not only literally impossible to have two mics that follow any kind of 3:1 rule to have an identical relationship to the source unless you're miking them from 20 yards away, and even then from that distance there'd not actually be any stereo image to capture, because it would basically for all practical purposes be a point source at that range.

G.

 

[mixsit]

..Invert the polarity on this quote so that everything is stated exactly the opposite, as if it's a quote from Bizzaro World, and you might have something close to the actual truth.
G.

Hopefully Soundchaser will come back and explain, ...well whatever the hell he was trying to say there.

 

[acidrock]

If you want to take it a little further....

http://www.littlelabs.com/ibp.html

 

[catchthatmonkey]

For me the best tip ive learnt so far for Aligning Two Mics to be in phase is from Michael Wagner which is to try to align them as identically as possible... then later.. flip one of them out phase... and then if u can hear... the quality gets bad...then.... its pretty much in phase... or u can flip the phase on one of the mics then move it around till u get that really in phase fat sound.

 

[pure.fusion]

For me the best tip ive learnt so far for Aligning Two Mics to be in phase is from Michael Wagner which is to try to align them as identically as possible... then later.. flip one of them out phase... and then if u can hear... the quality gets bad...then.... its pretty much in phase... or u can flip the phase on one of the mics then move it around till u get that really in phase fat sound.

Surely in this digital age, the method mentioned earlier in this post (that is still going!) would have to be easier, more accurate and less error prone than physically moving a mic and listening for the change in sound?

Moving the 2nd mic forward or backward from it position would be the same as dragging the 2nd wav file slightly left and right, no?

Cheers,
FM

 

[Todzilla]

Hey guys,

I'm going to try recording my guitar amp with two mics on the weekend - just for the experience and because someone gave me a condenser mic to play with.

Not to go into specifics about he methods of micing guitar amps, my question is about phase relation between the two mics - I've heard it mentioned many times but know nothing about it other than I have to "beware of it"

Lets see, from my high school physics, depending on the distance from the souce, the signals might be (I assume) anywhere between 0 and 180 drgrees out of phase? Is this correct?

So how do you make sure they're in phase? What's the go? What to I need to do here to make sure I'm doing the right thing?. Is there a standard method that people use in the studio?

Also, If I'm recording this one instrument, do I want to mix the result of the two mics onto one single track, or do I put them on one track each?

Cheers,
FM

Phase is also frequency dependent. So you could have two mics that are in phase at 1K Hz and out of phase at 60 Hz.

The easiest way to ensure phase is to have both mics in roughly the same place, but pointing in different directions, aka "The Coincident Pair." Often, however, that is not practical given multi-mic setups, like drums.

It takes a lot of patience to align phase in drums, not just through flipping phase buttons, but making sample level nudges to wave files. And then you can find the low end of the kick is in phase while the high end cymbals are "washy."

 

[SouthSIDE Glen]

Moving the 2nd mic forward or backward from it position would be the same as dragging the 2nd wav file slightly left and right, no?

There can be one important difference: moving the mic can change the nature of phase interference in the same signal that might be caused by room reflections, whereas once recorded, such interference is stuck in the recording no matter how you move it.

Granted, this is not always a problem, but when it is, it does make a difference.

G.