phase cancellation, proper mic setup

[random effect]

I need to know if there's any exact measurements for mic placement to avoid phase cancellation on a drum track. I'm going to be using two overheads, sm57 on snare, kick inside the head, and clip on tom mics. I've got a studio projects vtb1 coming in the mail and it has phase reverse on it but sadly, i only have an mr8 to run into so i can only do the kick seperate from the other drums but thats it. are there some general rules of thumb to abide by? any feedback is greatly appreciated. you guys have already taught me so much thanks, later

paul

 

[random effect]

ok i don't need exact measurements because there probably isn't such a thing but any close ideas?

 

[giraffe]

the big one is really the phase (mostly of the snare, brass, possibly kick... but the rest as well to a lesser amount) between the overs.

if it sounds smaller or thinner in mono than in stereo, you probably need to move one of the mics.

the phase reverse will be less useful than you think (unless double mic'ing the snare)

 

[random effect]

the further the mics are from eachother, the less phase problems correct? or is it how they're angled? I'm pretty much in the dark when it comes to phase correction and i know it plays a big roll in fuckin up a mix so i need to get some knowledge before i record my new demo... which is happening as soon as i get my preamp. hells yess

 

[littledog]

The most important parts of the pop drum sound are the kick and snare. The overheads won't capture that much kick, so you will be relying on the close kick mic, and maybe a room mic if you are using one. So phase is not as much of an issue here.

What will be immediately noticeable (in terms of phase issues) is the snare sound. If you are using a spaced pair (two mics seperated by a significant distance) one way to solve that is make sure both overheads are exactly the same distance from the center of the snare.

But make sure you understand what causes phase problems - it is what happens when the sound from a single source is picked up by two or more mics that are different distances from the source. That means that the closer mics are going to pick up the sound sooner than the more distant ones. Sometimes, like with a room mic, this is a good thing. Other times, it introduces classic "phasiness" or even comb-filtering into the sound. (So it sounds like you are hearing it through a guitar fx pedal).

One way to avoid problems is to use the 3:1 rule. That says that two mics picking up the same source are at least three times as far from each other as they are from the source.

A problem with the solution I suggested earlier (equal distance from the snare) is that, while snare phase issues are solved, there still may be problems with the toms or cymbals - all of which can't be equal distant from the same two mics.

Or can they?

In fact, there is a solution to that problem as well. It is called a coincident pair configuration. You set the overheads in a "V" shape so that the openings of the two capsules are practically touching. Because the two capsules are at essentially the same location, sound from anywhere on the kit will it both at the same time - so no phase problems. The size of the stereo field can be manipulated by how sharp the angle is between the two mic heads.

 

[jabulani jonny]

Littledog is correct, I'll take it a step farther. For what you're doing you should be able to get away with either 3 or 4 mics: kick, snare & 2 OH's. To help reduce phasing on your OH's (between each other) you can use a coincident mic setup such as XY or ORTF. These are probably the two most used coincident mic setups for OH. You can see diagrams here.

Are you mixing these tracks in a PC or on your standalone recorder? If on PC you can go in a manually line up the snare transient (hit) on the close mic with the snare transient on your OH. This will help make sure it's phase aligned once recorded. However, if you're mixing inside your standalone recorder and it doesn't give the option of viewing the waveforms of the different tracks, then you'll have to play around with the placement of your OH's a bit, ie. moving them closer to or farther from the drumset while listening to the sound of the snare. If you're in the same room with the drummer you're going to have to record and listen when he's not playing, making the adjustments between tracking. Again, the 3-1 rule could help out with this.

The fewer mics you use of course, the less phasing that you'll get so micing all the toms and the hi-hat may cause more problems than just putting up three mics, a kick & 2 OH's, or 4 mics as described above.

Like little dog said, your snare is where you'll probably here cancellations the most so that's probably what you should be listening for when adjusting the placement of your OH's.

These are just my thoughts and there are tons of techniques. Make sure to use the search function on these boards as drum micing has been covered many many times before with good advice on all of those threads.

Good luck!

Jonathan

 

[Uladine]

I've had a lot of success with the XY pattern on the overheads. While it's possible to get good sounds with a spaced pair, in my opinion the stereo field seems a little too wide when mixed with the rest of the music. I suppose the pan on the overhead tracks could be brought inward to tighten the field, but then you'd end up with a similar field that the XY pattern would give you, and you'd still have to deal with possible phase problems between the two mics if they weren't set up correctly.

I like to actually set the Overhead mics in an XY pattern a little above and behind the drummers head, almost as if it were a person standing behind the drummer, capturing what they'd hear. (watch out for those drumsticks!) Also this method tends to leave a "line of sight" so to speak to each sound source on the kit, so if the drummer has a ton of cymbals, there wont be a ton of crashes between say the ride and the overheads. Just my own personal experience, so take it with a grain of salt, but I thought I'd share what works for me. Of course if you can't time-align the waveforms in your DAW as mentioned earlier, you'll need to experiment more with the distance of the overheads to the snare.

 

[mixsit]

...But make sure you understand what causes phase problems - it is what happens when the sound from a single source is picked up by two or more mics that are different distances from the source. That means that the closer mics are going to pick up the sound sooner than the more distant ones. Sometimes, like with a room mic, this is a good thing. Other times, it introduces classic "phasiness" or even comb-filtering into the sound. (So it sounds like you are hearing it through a guitar fx pedal).

..A problem with the solution I suggested earlier (equal distance from the snare) is that, while snare phase issues are solved, there still may be problems with the toms or cymbals - all of which can't be equal distant from the same two mics.

With all due respect, if you understand those points...

One way to avoid problems is to use the 3:1 rule. That says that two mics picking up the same source are at least three times as far from each other as they are from the source.

..Why would you say that? 3:1 is not relevant in this context.

ok i don't need exact measurements because there probably isn't such a thing but any close ideas?

1) Once any two or more different path lengths combine some frequencies will always be out of phase. (Complex signals here, not single pitch.)
2) As the distance difference increases from zero, phase cancellation begins in the high frequencies and extends and includes lower and lower tones, into the midrange with in several inches.
3) If the far pick-up is well into the reverberant field, the added reflections tend to average out the simple path (time) interferences.
4) Our choices are to choose the more pleasing interferences (pitches) and the depth of the interference (relative volume)

Wayne

 

[random effect]

ok so i think im gonna go with the xy overhead pattern bu what about clip on tom mics? should i even use them at all? will it cause more phasing than they're worth are none at all because of the three to one rule?

 

[mixsit]

ok so i think im gonna go with the xy overhead pattern bu what about clip on tom mics? should i even use them at all? will it cause more phasing than they're worth are none at all because of the three to one rule?

XY is slightly easier to deal with than some other overhead placements because it at least keep those two kit mics in phase with each other. But issues with the mix of close mics is the same. So in general it still applies- close mic the ones where you want the added up front focus, at distances that sound good. If the kit, snare and kick mics do it, keep it simple.

Here's why 3:1 falls on its face (in this application). Take a close mic at 2". 3:1 says anything from six inches on out should be... what, fine? The thing is, it is distance difference (which is time difference) that decides which frequiences cancell and boost. 3:1 is simply a ratio that says nothing about what your distances are.
3:1 is about attenuating overlapping signals by way of distance to the sources vs distance to the other mic where you want to hide the combined interference.

 

[metalhead28]

One point that you should grasp first and foremost, which is evident in some of these posts but not specifically pointed out, is that the "phase" switch you mentioned on your pre-amp it's not really a "phase" switch but just a polarity switch.
Polarity is an absolute thing, phase is frequency dependant. Flipping the polarity 180 degrees might make certain frequencies reinforce each other a little better, and some might get worse.

Aligning for phase is often going to be a compromise with complex sounding sources. Having a polarity switch will give you 2 distinct choices for phase aligning two tracks, but that doesn't give you a definite solution.

I guess what I'm saying is, don't ever depend on that, the only solution is taking the time to position the mics.

 

[bennychico11]

One point that you should grasp first and foremost, which is evident in some of these posts but not specifically pointed out, is that the "phase" switch you mentioned on your pre-amp it's not really a "phase" switch but just a polarity switch.
Polarity is an absolute thing, phase is frequency dependant. Flipping the polarity 180 degrees might make certain frequencies reinforce each other a little better, and some might get worse.

I'd admit that I once thought this too (and mistold several people on here the same thing myself)...but then I had a discussion with cpl_crud, Farview and then later with Glen and a few others, in where I learned there is much more going on in the scientific/phsyics/math world with a phase reversal. Basically what came from it is that we are dealing with complex wave forms where phase is dependant on angle and not time. It's only manifested as a time difference. So a phase/polarity reversal button does physically switch the +/- pins for us, but this also shifts the phase angle of our signal swinging it in the reverse direction on the complex plane. So it can correctly be called a phase shift.

I can give you a link of our discussion if you'd like.

Aligning for phase is often going to be a compromise with complex sounding sources. Having a polarity switch will give you 2 distinct choices for phase aligning two tracks, but that doesn't give you a definite solution.

THIS, however, I do agree with. And come across it frequently. In these instances is may be beneficial to delay a track (either by using a delay or physically moving the wave in a workstation) as well as flipping the phase. I usually just physically move it anyway to correct for the time difference, however I just came across some location audio stuff where I had to physcially move the tracks as well as flip the phase of it. The original guy recording it could have had a phase switch already pressed in on the mixer or could have been using a poorly wired cable (more likely the cause).

 

[metalhead28]

I'd admit that I once thought this too (and mistold several people on here the same thing myself)...but then I had a discussion with cpl_crud, Farview and then later with Glen and a few others, in where I learned there is much more going on in the scientific/phsyics/math world with a phase reversal. Basically what came from it is that we are dealing with complex wave forms where phase is dependant on angle and not time. It's only manifested as a time difference. So a phase/polarity reversal button does physically switch the +/- pins for us, but this also shifts the phase angle of our signal swinging it in the reverse direction on the complex plane. So it can correctly be called a phase shift.

Interesting, and I'm sure you're right. I wouldn't pretend to be equipped to argue that point, I just thought that saying "flipping the polarity" created a clearer picture in one's mind that it was an absolute change and that it wouldn't necessarily put things in phase that were out of phase....it's much more complex.

I won't criticize anybody else for calling it a "phase" switch, haha. But I'll still try to make them understand what they're doing.

Thanks

 

[random effect]

i appreciate all the word of wisdom guys but do you think the tom mics will give me any trouble? they're all at least a foot away from eachother and clipped on about 2 inches from the head so i figured the source signal would be strong enough to eliminate phasing issues.. thoughts? opinions?

 

[mixsit]

i appreciate all the word of wisdom guys but do you think the tom mics will give me any trouble? they're all at least a foot away from eachother and clipped on about 2 inches from the head so i figured the source signal would be strong enough to eliminate phasing issues.. thoughts? opinions?

If you don't mind, I don't.. One more.. If you were thinking '3:1 between just the tom mics, then yes, the phase effects between those will be attenuated -but not from the overheads.
Measurements are not the answer here. Even if you set mics as per 3:1, as soon as you compensate for the close/far distances with volume (i.e. mix them back in) you are smack dab back to finding placements that sound good with the phase effects!
Try to see this again- Distance determines the frequencies effected, relative volume sets the depth (or strength) of the phase effects.
There is no getting around this. But it still works fine. Go for it.