Huh? Reverse phase on ALL mics?

N

nddhc

New member
I read this article about drum recording - im trying to learn as much as I can about recording drums in general.

http://www.eqmag.com/story.asp?storyCode=15638

This article says that you should reverse the phase on all the mics, except the kick.. Heres the quote if you dont feel like reading it -

"(Note that you should also reverse the phase of all mics on drums that are miked from the top of the sound source — the only mic that sees correct phase is the kick — air moving towards the diaphragm at initial attack.) "

Why is this? Maybe this should have been posted in the newbie forum..
 
I'm not going to read the article, but it's a ridiculous premise. The movement of air and the projection of sound waves are not the same thing. When a stick/beater/whatever hits a drumhead, sound radiates in all directions. The reason that you might want to flip the polarity/phase of certain mics has to do with their relative distances from the sound source, not which side they are on.
 
Phase is a relative term. You have to have something else to be in phase with. I get what he is saying, but isn't going to make any difference at all.
 
scrubs said:
I'm not going to read the article, but it's a ridiculous premise. The movement of air and the projection of sound waves are not the same thing. When a stick/beater/whatever hits a drumhead, sound radiates in all directions. The reason that you might want to flip the polarity/phase of certain mics has to do with their relative distances from the sound source, not which side they are on.
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Sorry Scrubs, but I disagree. The movement of air and the projection of sound is one in the same. The only way sound can travel through the air is by molecules vibrating back and forth in reaction to the source vibration. In this case the molecules follow the same movement patterns as the drumhead does.

If you slowed it all down and observed the vibration movements one at a time, during that moment in time when the drumhead moves toward the mic, the mic's diaphragm is pushed in that same direction by the sound pressure wave, (i.e, the moving molecules.) When the drumhead changes direction and moves away from the mic, the diaphragm gets pulled back toward the drum. So the mic diaphragm moves up and down almost exactly the same as the drumhead. Furthermore, the bottom drumhead also follows that same pattern. Both heads move together in unison.

If the mic were turned around and placed at the bottom of the drum, the movement pattern would be the opposite as it was on top, (or in opposite phase.)

But, Farview may have a point. We are probably splitting hairs as far as drum tracks sounding better that way.
 
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RawDepth said:
Sorry Scrubs, but I disagree. The movement of air and the projection of sound is one in the same. The only way sound can travel through the air is by molecules vibrating back and forth in reaction to the source vibration. In this case the molecules follow the same movement patterns as the drumhead does.
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I don't believe that necessarily means that two mics facing from either direction will be out of phase. Distance is a factor.
As Farview said, phase is relative.
 
eraos said:
I don't believe that necessarily means that two mics facing from either direction will be out of phase. Distance is a factor.
As Farview said, phase is relative.
Click to expand...

If you mic a drum head from both sides, and the mics are the same distance away, they will be reversed in polarity if you look at the waveforms, like Rawdepth explained. If they are different distances, they will be out of phase in the time domain.

This is why when micing a snare from top and bottom, reversing polarity on one mic and getting them the same distance from the heads is recommended. Both mics will hear the source in the same polarity, and be very close in the time domain. This hopefully keeps cancellations to a minimum.

As far as the article, I'd say play around and see if it makes a difference. Since the mics on a kit are separated in distance, and therefore time, there will by definiton be some comb filtering. Whether or not flipping polarity of any given mic in that situation improves or hurts the overall sound entirely depends on kit setup and mic position. Realize that every recording situation is going to be different, and no hard and fast rules are going to work every time.
 
speaking of Kit micing...

if you time align mics after tracking, then it's beneficial to polarity adjust to a reference. I use the overheads... therefore the Kick (if mic'd inside) and all bottom head mics get adjusted.

scrubs said:
...but it's a ridiculous premise. The movement of air and the projection of sound waves are not the same thing. When a stick/beater/whatever hits a drumhead, sound radiates in all directions. The reason that you might want to flip the polarity/phase of certain mics has to do with their relative distances from the sound source, not which side they are on.
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I disagree... and this can be easily seen... mic the top and bottom of a tom. The top mic will see a negative going pulse and the bottom will see a positive going pulse. this matters and especially if you time align. one mic (track) should be polarity adjusted.
 
Sonixx said:
if you time align mics after tracking,
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Don't you find that that colapses the sense of space around the drums? Maybe i wasn't doing it right, but the overheads are supposed to be farther away and therefore delayed. It never sounded right (to me) when I lined everything up.
 
I will always check the initial polarity of the the different mics, such as both overheads with each other, toms etc to make sure the initial transient all push up positive.
I'll genrally leave the time alignment alone (so the depth does not collapse) unless it is the top and bottom mic for the same drum.

I guess my thought behind it is I want that speaker punching out at me with each kick and hit, and not pulling in when the Bass guitar is pushing out on the downbeats.

It may sound dumb... but it works for me.
 
I really don't understand how a mic on a tom and a mic on the kick can be out of phase with each other. They always play different frequencies and are usually hit at different times. Isn't it impossible for two different frequencies to be in phase with each other, no matter where the mics are placed?
 
RawDepth said:
I really don't understand how a mic on a tom and a mic on the kick can be out of phase with each other. They always play different frequencies and are usually hit at different times. Isn't it impossible for two different frequencies to be in phase with each other, no matter where the mics are placed?
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You are probably right.
I think What most people are talking about is the same drum being in phase where it is being picked up by different mics.

I'll sit at my kit and put all the mics in record and smack the crap out of the snare then thump each piece of the kit one at a time. When I look at the recrded tracks I amd looking to see that the snare shows the same polarity in each track where it bleeds, or at least that if the time alignment is far enough to where the sanre wont cancel itself out when I bring up the tom tracks. Same with the kick. If the snare mic picks up the kick in reverse polarity and the time alignment is really close, when I add the 2 together the kick sounds wimpy because of the cancellations.

Again it is nearly impossible to coax all the tracks to be in perfect phase with each other, hense the suggestions of recording with the fewest amounts of mics that you possibly can to geet the sound you are after.

In the end.... you HAVE to use your ears.. the waveforms cant tell the whole story. One time I spent HOURS aligning tracks so that the wave forms looked theoretically good and in phase.. It sounded like hammered dog doo...


Tom
 
ez_willis said:
So if a tree falls in space, it wouldn't make a sound?
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A tree in space would be constantly falling. Until it hits something, it wouldn't make a sound. Once it does, it depends.
 
call me a crazy visionary, but isn't this entire universe of recording about trying different things and finding out what works? ok, so swap the phase of every mic except the kick. does your recording now sound better or worse? was it a good or bad idea? this is what drives me crazy about various pundits and critics putting out these "rules of thumb." generalities may be helpful, like, "try cutting 250 Hz by 2-3 dB on the kick drum, for this is the fundamental frequency of a kick drum." but this advice doesn't take into account the diameter, depth, wood, heads, etc. of that kick drum. IT'S A GENERALITY!!!! these may be good for pointing us in new and different directions, but ultimately the recording that we apply this advice to is proof of whether or not it's GOOD advice! so, i know it's been said a million times and is loathed by all of us looking for shortcuts, but--only experimentation will really answer your question. this is why there is no replacement for EXPERIENCE! believe me, i've tried finding shorcuts. there are none. we all have to live with that, even though it means we're totally frustrated with how slow our progress is made. enjoy finding out on your own if swapping phase sounds better. then your question will be answered.
 
Keep all mics normal on way in.
After recording listen for what might need the phase flipped.
Try out flipping the kick. If it doesnt make a difference then it doesnt make a diference. :)
Eck
 
I think that last post sums things up nicely. If you record everything and something sounds dead or thin, try reversing the face of the mic the source was recorded with. If it fixes the problem, great! If not, go back and try a new mic positioning scheme.

As for the air movement thing... there seems to be a difference AND a correlation between air movement and air molecule vibration. Think about using a pop filter on a vocalist. The pop filter takes the actual burst of air and diverts it away from the mic. What you are left with between the filter and the mic is simply air molecules vibrating from what was left resonating after most of that air was diverted.

So, you don't want to think that the air from the bass drum hole is the direction the sound is going - that is simply the pressure being released from the drum on drumhead strike, which technically makes the chamber in the drum smaller. If you put the hole in the shell on the side, the air would come out there, but that's not where most of the sound is coming from... most of the sound is coming from that resonating drum head, which is still on the front of the bass drum (and the back, too, I know I know).

If it were the case that the direction of air release were the direction of the sound, every one of your toms and your snare drum's main sound output would be that tiny air vent on the shell of the drum... but it is clearly the resonating head that gives the sound output. Just the ole .02
 
In terms of the pop filter thing though, I think it might not be as much of a difference as you might think. The sound and the pop are all movements of air - the only difference is that the pop blast of air is a low frequency high amplitude component of the sound. Basically the pop filter cuts out anything too strong in the low end (and I'm talking like orders of magnitude higher than the rest of it).

Thinking about it in that sense, it's really not so different. Just a humongous amount of energy down toward zero frequency that can manifest itself in all sorts of ways once it's picked up by the mic.
 
OK, I have tried this trick the first post is talking about. But I just flipped the phase on the kick. It is easier to do that then all the other mics and it does the same thing. The resault was that the bleed from the other drums was greatly reduced but there was a bit of filter affect. ;)
 
Farview said:
Don't you find that that colapses the sense of space around the drums? Maybe i wasn't doing it right, but the overheads are supposed to be farther away and therefore delayed. It never sounded right (to me) when I lined everything up.
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that's why I prefaced the statement with if...

I do mostly close micing and the overheads capture the cymbals and I'm not looking for ambiance. yes I agree.
 
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