Dual micing

[Muffin]

Good evening,

It's been awhile since I've been on here, and I'm not sure why I've been absent, I love it here.

Anyways, I'm going to ask a question that I'm sure you've answered before, however my searches haven't exactly answered them all.

I got myself 2 SM57's, based on a number of reviews I've read and videos I've watched, these seem to be a great pair for cabs and snares and that's exactly what I'd like to use them for.

But, how do you get them 'synced' or 'in phase'? I've tried a few things but I'd like to know from you which method is best and produces the best results.

First, I tried adjusting it after recording. I dual mic'd a cab, then zoomed onto the 2 tracks in my DAW(Cubase 5) and slid one to match the other. I noticed that any adjustment made to the layout of these tracks drastically changed the overall tone of the guitar.

I've also tried adjusting the mics, however I'm having a hard time knowing when their in there sweet spot. Should I have the guitarist play with mics in place, me sitting at the computer zoomed onto the tracks being recorded and tell an assistant to adjust the mics until the sound waves that I'm seeing in my DAW line up? I guess as a similar method as stated above?

Lastly, what does phase (invert,flip or reverse) do? and in what situations would you need it?

Thank-you all in advance!


EDIT: I forgot to ask about overheads for drums as well. I had an engineer tell me to keep the mics close together. Meeting in the middle over the drummer with the tips of the mics nearly touching each other. Any help with phasing overheads would also be swell!

 

[bouldersoundguy]

Consider the fact that through almost the whole history of sound recording it was not possible to alter the time relationship between two mics once recorded, and yet many thousands of excellent recording were produced. In other words, it's possible to get it pretty much right during tracking.

When double micing a cab, set the mics the same distance from the speakers. You shouldn't have to realign them digitally, but you can certainly experiment for tonal effects. Which brings me to another important point. If it sounds good it is good regardless of what rules you break.

For overheads you have two choices: coincident pair or spaced pair. A coincident pair will have no phase problems between the two mics (though it might interfere with other drum mics), but a spaced pair will have some phase interaction. Which brings me to a third important point: the 3:1 rule. Any time you have two or more spaced mics picking up a common source you should try to make sure all the secondary mics are at least 3 times the distance from the source as the primary one. When I go for spaced overheads I tend to think of them as cymbal mics rather than overall kit mics, and I tend to put them lower over the cymbals for maximum separation. I try to make sure that the right overhead is at least 3 times the distance from the ride as the left overhead. With enough separation phase interactions are inaudible.

Remember that your ears always trump your eyes. Don't stress about how the waves look, listen and decide.

You can't flip, invert or reverse phase. It can only be changed by degrees@frequency. What they are talking about is actually polarity, a related but different thing. Sound is waves of positive and negative pressure. Microphones convert that into positive and negative waves of voltage. Most mics produce a positive voltage with positive air pressure, and negative voltage with negative pressure. When you swap the positive and negative sides of a wave it's called inverting (flipping, reversing) polarity. In a waveform display it looks like the wave is flipped upside down. When two identical waves are put out of phase the negative side of one sometimes lines up with the positive side of the other. Two waves with opposite polarity do something similar. The difference is that with phase they are mismatched at some frequencies more than others, while with polarity they are perfectly mismatched at all frequencies. The reason "phase" is often confused with "polarity" is that problems with the former are often treated with a flip of the latter, with varying results.

 

[Armistice]

Welcome back Muffin...

There are smarter people around with mics than me, but for my $0.02 - I wouldn't ever be trying to "sync" the two signals from two mics on the same source by aligning them in the time scale. What I would do is, if I think phase variations are occurring, is invert the polarity of one of them (you do this in your DAW normally) which basically just flips the waveform upside down. On its own it sounds the same, but when blended with another mic on the same source, minimises phase interference...

There's plenty of stuff around here about it and on the web. Do a bit of googling and you'll be up to speed in no time.

I'm also not sure of the wisdom of dual micing a guitar cab with 2 (almost) identical mics - if I do this at all, I put an SM57 on the grill, and an LDC a couple of feet back to get some "room"...

Cheers

 

[inwiththeold]

try sychronizing the bit rate of your interface with your computer. I could see it getting confused or something.

 

[Steenamaroo]

The waveforms will only line up when the mics are at exactly the same distance from the amp, in the same direction.
It's not a rule to have them line up though. The placement difference is what creates the unique tone, so try a few things but use your ears and get a sound that you like


For more info/a better understanding though, i'd suggest going and reading a section from a book on audio physics or audio recording. Read something that explains in detail the difference between phase and polarity, and the common methods of, and reasons for altering these things.

I know that's the 'easy answer', but it's a confusing topic, and i imagine the answers from this board are almost certainly just going to confuse matters moreso.

Someone suggested inverting the polarity of 1 mic, and while this may 'help' in some cases, it should not be considered a 'one size fits all' remedy for phase issues.
I only ever invert the phase of a mic if i'm recording something from two different sides...like guitar cab front and back, or snare top and bottom. (Maybe this is what you're talking about??)



In response to your edit, you shouldn't be having phase problems with your overheads if they are both the same distance from the kit. Phase problems come from a source of sound reaching two microphones at different times; so yeh, technically there'll always be some degree of difference, but it shouldn't affect your overheads in this case.

 

[Muffin]

Lots of great information, thank-you all for your insight!

I can see that mic setup takes a lot of practice and I'm working at it. I just finished recording an album for my band and we got it professionally mixed and mastered. I asked him how the tracking was and he said their was phase issues on the cabs, snare and overheads. Basically how he described it(on the snare atleast) was to picture a speaker with a strong hit. The speaker will in and out creating the sound and allowing it to 'breathe'. My mics were out of phase so the bottom mic would cause the speaker 'hit' as the speaker was already pushed out from the top mic drowning it out.

I have a small(and basic) home recording studio in my basement. My computer is in a separate room from the studio but it's not sound proof so I wouldn't be able to have the audio playing through my monitors during sound check to check for phase issues. Is the second method that I mentioned in my original post the(a) proper way to check for phase issues?

 

[Muffin]

Sorry I forgot to mention.

With the overheads, I've seen people measure the distance of their mics from the pedal beater with a string(one over the left side, and one on the right). My overheads are primarily for cymbals, all other drums are close mic'd. Would it be best to keep them closer together, or on the sides?

 

[Armistice]

I think boulder gave you some info on that up top...

 

[Steenamaroo]

Basically how he described it(on the snare atleast) was to picture a speaker with a strong hit. The speaker will in and out creating the sound and allowing it to 'breathe'. My mics were out of phase so the bottom mic would cause the speaker 'hit' as the speaker was already pushed out from the top mic drowning it out.

This is the situation where you'd reverse the polarity of one microphone.
Because one mic is on top and the other is on the bottom, it means that what one mic perceives to be a positive signal, the other perceives as negative, so much of the sound is cancelled out.

All you do is invert the polarity of one mic in your software.
It's best to invert the bottom mic i guess, since the overheads are also above the snare.

Hope that helps.

 

[Farview]

Why are you putting two identical mics on the same source? What are you trying to achieve?

I always double mic the guitars, but I use a 57 and a 421 because the two mics compliment each other.

All you need to do to get the mics phase coherant is place them the same distance away from what you are recording. Just put them next to each other and line them up. It's that easy.

Like other people have pointed out, you don't necessarily need the mics to be phase aligned. Having the phase cancellation alter the sound might give you the sound you are looking for.

For overheads, putting the mics in an XY setup over the snare is a good way to go to give you a good coherent stereo image of the kit. A spaced pair will give you more separation of the left and right with less snare in it. It is a good idea to make sure that the two mics are the same distance from the center of the kit (usually the snare)

 

[IK Obi]

I think on guitar cab your fine with just one mic. When using two flip your master buss to mono and check and see if it sounds funny or loses low end. If it does move it til it sounds fine. Then flip it back! 2 mics in phase!

 

[Shadow_7]

As previously stated, you want the mics equal distant from the intended source. If you're on opposite sides of a sound diaphragm, you want to invert one of the tracks before mixing. i.e. Speaker cones, or drum heads, or ....

Being off by a few inches (or less) in distance can affect how things mix. You can time shift things in post to compensate for distance a little bit. Just line up the waveform visually at high zoom in your audio application. The speed of sound is kind of slow, so being off by say a foot could be the difference between standing on the sidewalk, or standing in the middle of the road. Ones all butterflies and flowers, the other faces of asphalt.

The speed of sound varies, but basically 1,100 feet per second. At 48000 samples per second. That's almost 44 samples per foot difference. Or almost 4 samples per INCH. That's enough to have at least a visual difference when compared side by side in an audio editor at high zoom. You can adjust in post, and with having to be < 1/4" difference to be semi-perfectly aligned, you'll likely need to adjust. Unless of course the desired sound is achieved. Phase issues and comb filtering effects will abound by even a small difference. And are probably not avoidable anyway because of room reflections, but you do have some control over that with distance, time shifting, and other things related to phase.

 

[mixsit]

...What I would do is, if I think phase variations are occurring, is invert the polarity of one of them (you do this in your DAW normally) which basically just flips the waveform upside down. On its own it sounds the same, but when blended with another mic on the same source, minimises phase interference...

If I may inject..

..This would be whenever the two sounds are most likely naturally inverted from the two positions as for example where you are micing from opposite sides of something.

Otherwise.. .... -In all cases-..... Where there is time offset there will be 'phase issues' (or otherwise know as the desired chosen tone.. ) at some frequencies. In these cases (very often?) inverting one is just a different combination of 'out of phase.
This seems to be a tough one to get our heads around, but OMHO it's worth taking the time to get this one down 'cause it leads to some clarity in a lot of other micing conditions.

 

[Supercreep]

I align my room mics and overheads with my snare mic routinely.

 

[Muffin]

Wow, lots of different techniques, thanks for that.

Farview, I know that using 2 identical mics may seem unnecessary, however seeing as the positioning of each mic effects the overall tone the 2 mics wouldn`t be aligned the same. I watched a few videos about micing cabs and discovered that many were dual micing just 1 speaker. In this particular video he had 2 SM57`s both about 6 inches away from the cone, one dead center, the other right beside but angled inwards also pointing towards the cone.

Their seems to be a bunch of different techniques for mic placement and I`m betting I`m just going to have find a method that I`m happy with.

You have all given me a bunch on info on placements and I thankyou for that. I think I know what to do now for the snare and cabs.

I`m still just a bit lost with the overheads. These overheads are just to pick up the cymbals, left and right, I want as little snare, toms and kick as possible going through them. That being said, I should separate the 2 mics then correct? One over the right and one over the left?

I appreciate all your patience with my noobishness.

 

[bouldersoundguy]

I`m still just a bit lost with the overheads. These overheads are just to pick up the cymbals, left and right, I want as little snare, toms and kick as possible going through them. That being said, I should separate the 2 mics then correct? One over the right and one over the left?

That's what I'd do if separation were my goal. Use distance and pickup pattern to your advantage.

But I don't do that with all kits. The ones that need the most help sonically are the ones I approach with a "divide and conquer" attitude. Drums that sound good generally need fewer mics, using the overheads for the overall sound and filling in with a kick and snare.

 

[bouldersoundguy]

Where there is time offset there will be 'phase issues' (or otherwise know as the desired chosen tone.. ) at some frequencies. In these cases (very often?) inverting one is just a different combination of 'out of phase.
This seems to be a tough one to get our heads around, but OMHO it's worth taking the time to get this one down 'cause it leads to some clarity in a lot of other micing conditions.

To add:

Phase interference doesn't only result in cancellation (destructive interference), it also causes addition (constructive interference). If you use polarity to address phase problems what happens is a reversal of constructive and destructive interference: where it added it then cancels, and where it canceled it adds. So you don't really solve the problem so much as change the problem to one that may or may not be more acceptable.

 

[Supercreep]

I`m still just a bit lost with the overheads. These overheads are just to pick up the cymbals, left and right, I want as little snare, toms and kick as possible going through them. That being said, I should separate the 2 mics then correct? One over the right and one over the left?

Why? A drumset is a single instrument. If you want to just capture cymbals, then just play cymbals. The overheads should capture a stereo image of the entire kit. The close mics should supplement that image.

 

[RAMI]

Why? A drumset is a single instrument. If you want to just capture cymbals, then just play cymbals. The overheads should capture a stereo image of the entire kit. The close mics should supplement that image.

Exactly. They're called "overheads", not "cymbal mics". If you want "cymbal mics", then that's a whole different story. But I'd say that 90% of your drum sound should come from your overheads (ok, maybe 72.4% or 85.7%...whatever). But MOST of your drum sound should be about your overheads, with the spot mics enhancing that.

It might be different for live work, but for recording, I'd say 99% of engineers (or maybe 82.5% or 89'3%...whatever) use overheads as OVERHEADS, not as "cymbal mics".

 

[bouldersoundguy]

Why? A drumset is a single instrument. If you want to just capture cymbals, then just play cymbals. The overheads should capture a stereo image of the entire kit. The close mics should supplement that image.

That's an unrealistically narrow view. If that were true then the spot mics would be superfluous. Why would anyone care what the "overheads should capture"? If using the mics on the cymbals gets the best result then that what he "should" do.

Some music requires a fair amount of specific processing on drums that only works with adequate separation. Other music simply requires the drums to be recorded as they are. They demand very different mic placement.