Drums, phase and wall reflections

[Tubeguy]

I've got this thing with phase on drums. For example: I might have close snare mic and about over a meter high overhead mic. Nothing else, it's just en example. I play the two tracks, switch phase on one of them and the snare becomes fatter and punchier. That sounds like a phase issue but how can it be when both mics are pointing at the snare? Wall or ceiling reflections creeping in?
I use the phase to shape my drums so it's no problem but I just want to know what's going on there and can't find any plugin that would visually show me. It drives me nuts.

[martifingers]

I am no expert (they will be along shortly I would guess) but isn't it all about distances rather than direction?
I don't think the room reverberation is a big factor but could be totally wrong on that.

[Tubeguy]

I'd say the distance would matter when you have two mics in stereo overheads. I don't think I'm getting full phase cancellation, just partial but it's enough the make a difference.
And did I mention that my drums are in partially padded corner of a fairly large live sounding room

[jrk]

1st of all, check that your 2 mics have the same polarity , that the cables aren't wired wrong,etc.

Easy way to do this is to have them the same distance from some nice impulsive sound (like a click, whatever) record them and see if the waveforms line up nice (do they both go 'up' together?)

(or, if you're sure about the distance any sound will work, you get the idea)

OK, now, when you're sure your mics are responding similar...

If you think about it, given a close mic (pointing down at the snare) and an overhead (likewise) the predominant effect on "phase" is the difference in distance that the sound has to travel to reach them. If this distance is about a meter, then the difference is about 3ms - this will produce comb filtering - changing the sound a lot. Flipping the polarity will change the sound of this, giving you a filter with peaks where there were troughs.

Reflections from the room boundaries interact in similar ways. They're generally somewhat quieter than the direct sound and there's lots of them (lot's of paths with multiple reflctions). The'll tend to obscure the comb-filtering effect that would probably be wildly objectionable in an anechoic room.

Some folks time-align their overheads / align their close mics to the overheads / however you look at it. JUst look at the wave forms and drag them around until they line up best. Initial transients line up / everybody going up and down together / flipping polarity if you need to. And some don't. Whatever works for you.

[beingmf]

As a general rule for myself I always have the "JS Phase Rotator" on at least the snare channel. That's my main sound shaper. It gets interesting when you add an EQ, most of the time I need to readjust the phase.
Also setting up an allpass filter in ReaEQ is working great sometimes.

[karbomusic]

That sounds like a phase issue but how can it be when both mics are pointing at the snare?

It's about distance whether the mics differ in distance from the source and/or due to walls. With snare vs OH mic, differing distance comes with the territory, if flipping the polarity sounds better, do that, that's what the button is for.

[serr]

Originally Posted by Tubeguy

I've got this thing with phase on drums. For example: I might have close snare mic and about over a meter high overhead mic. Nothing else, it's just en example. I play the two tracks, switch phase on one of them and the snare becomes fatter and punchier. That sounds like a phase issue but how can it be when both mics are pointing at the snare? Wall or ceiling reflections creeping in?
I use the phase to shape my drums so it's no problem but I just want to know what's going on there and can't find any plugin that would visually show me. It drives me nuts.

They may be pointing the same direction and both mics are picking up the sound in positive phase, but the time difference leads to comb filtering when mixing the two different time streams. Flipping the polarity on one simply swaps the comb cuts to adds. And it turns out to be more supportive than destructive in the lower frequencies.

If you approach this by going for the main drum sound from the overheads and just use the close mics for emphasis (possibly nudged into phase with the overheads - possibly not touched! - this really depends...), you'll maybe have an easier time.

Old school: Push the polarity buttons or whatever until it sounds right and print that!
Computer age: If there's time, you can put all the pieces together and work any phase/timing to be transparently perfect.

[ashcat_lt]

It's not so much distance as relative timing and level. Just so happens that both of those things are connected to distance.

The real actual problem is that the overhead is not a lot further from the snare than it is from the rest of the kit. If you used a matched pair of mics (not that you would, just follow me here) and made sure they got exactly the same gain at the pre, and brought them up at unity, you wouldn't have any noticeable phase cancellation because the snare from the close mic will be a hell of a lot louder than from the OH. It'll also be a hell of a lot louder than the rest of the kit, so you'll turn it down. Oh, who am I kidding? We all know you're going to turn the OH up instead. Either way, you have changed the relative level between the two and at a certain point the two delayed copies of the snare end up close enough in level where the phase cancellation is noticeable. It was actually happening the whole time, but the comb filtering was so shallow that we didn't notice until they came within about 9-10db one way or another. Unfortunately, that's usually right around where we want to be because otherwise one or the other mics isn't really contributing enough to be worth it at all. So...

I am one who will align those snare waveforms in most cases. I kind of understand why some people don't, but I usually prefer it. I mean, I'd rather not have a close snare mic at all, but this is also true for kick drums, and I usually do want a mic there.

Reflections cause phase issues when they are loud enough compared to the direct sound that the comb filtering matters and fast enough that it falls within the audible spectrum. An overhead mic that is just the right distance from a reflective ceiling can make a big mess. But because the delay time is usually shorter than that between OH and snare, the mess is usually in the upper mids and treble region. It's the reason so many basement drum recording sound so weird, especially the cymbals. It doesn't affect the low end near as much. Unfortunately there's nothing you can do about that except move the mic or treat the ceiling. Once it's recorded, it's baked in. You can't nudge it in time or volume because it's all happening physically in the air at the diaphragm of the microphone and basically just part of that one source.

I dont find phase rotation to be the best solution to this. Changing the delay time is the only way to make sure that all frequencies are in phase. Phase rotation changes the delay of some frequencies but not others, making things far less predictable. It kind of only works on accident, and sometimes just shifts the comb filtering to different frequencies. Often I suppose, that's all it takes, and if it works for you, do it. It WILL affect the sound, and can be powerful, but I prefer to go other ways most of the time.

[karbomusic]

Originally Posted by ashcat_lt

It's not so much distance as relative timing and level. Just so happens that both of those things are connected to distance.

Duh.

The real actual problem is that the overhead is not a lot further from the snare than it is from the rest of the kit.

It's like I'm in pedantic/symantic hell or something.

[ashcat_lt]

Originally Posted by karbomusic

It's like I'm in pedantic/symantic hell or something.

Naw. Just remedial acoustics.

[Tubeguy]

Great replies thanks. So basically a comb filtering, it never crossed my mind. I didn't think distance would cause this unless it's stereo mics.
Now I can sleep better knowing what it is.
I normally mic from distance but have close mic on snare for adding punch, this is where the comb filtering happens. Switching phase on the snare mic can make it fatter. But it also depends on how hard I play the snare, not much difference when I play softly.

[BigFella]

https://www.youtube.com/watch?v=4qgm...ature=youtu.be

https://www.youtube.com/watch?v=FFtx...ature=youtu.be

Turn your 'phones down for the 2nd one, it's pink noise.

And my fave Dave Rat vid (more p/n):

https://youtu.be/VHjdh-Vka-g

[ChristopherT]

To work this problem out it is just about the right process to find the phase issue(s).
There are too many things interacting to cause phase problems.
Start with Kick and snare - make sure these are in phase, then add each mic from that point.
If you find any phase issues - move/change/alter the the last mic that you added until this is in phase - repeat.

But you may end up needing to move the drumkit angle if you cannot resolve the phase issues that arise.

It's all about the mics

[martifingers]

Instructive answers as expected. One point about room reflections. Are these less obtrusive not only because they are quieter but also because they are more "natural" given that they presumably occur in any real environment regardless of the presence of a microphone?
I suppose at this point we are into the world of room treatment...

[jrk]

Originally Posted by martifingers

room reflections. Are these less obtrusive not only because they are quieter but also because they are more "natural" given that they presumably occur in any real environment regardless of the presence of a microphone?
I suppose at this point we are into the world of room treatment...

reflections are probably "less obtrusive" not only because they're quieter but also because there's more of them. Except in pathological cases they'll tend to average out somewhat - giving you the 'room sound', and masking strong comb-filtering effects. I'd guess.

and of course, the're effectively longer delays than the inter-mic distances, typically.

I wouldn't stick drums in a "padded corner" as a first choice. Pick the spot that sounds best. It doesn't appear that this corner is really working for the OP.

[Jack Ruston]

As explained, the main issue here is that you have two mics, at different distances, strongly presenting the same source.

BUT in fact the room plays a role in all this too. Even with a single drum, and a single mic, the reflections within the space will combine with the direct sound at the mic, affecting the sound dramatically. There are spots within a room that sound subjectively 'fatter' or 'thinner' because of the way this interaction occurs. Even with a very dry room, unless it's extraordinarily well designed and built, there will typically be less control of the low end reflection than there is in the highs and mids.

So first, position the kit within the room in a spot where it sounds solid, punchy, weighty. Then position the more distant mics like overheads and room mics in such a way that they reinforce (or cancel) strongly with the rather more fixed close mic positions. This is a jigsaw...the ideal position for the overheads in relation to the snare might not be the ideal in terms of the rack tom, for example. I'd prioritise the snare, and flip polarity on the other mics, choosing the subjectively better option. There are things you can do later to 'twist' the phase relationship of a given pair of mics.

In my view, the time aligning thing sounds very un-natural, but each to their own.

J

[karbomusic]

Originally Posted by Jack Ruston

In my view, the time aligning thing sounds very un-natural, but each to their own.

J

That's my opinion as well. My theory is that aligning is trying to account for one misalignment but it's effectively moving every surface reflection in time as well - YMMV on how much that matters - I will post-align a couple of mics on a guitar cab (if needed) while trying to get bot mics at the exact distance but there aren't wall reflections of substance to deal with there. Since I already know where the elements in the mics are, I usually don't have to post-align them anyway as I can usually get them within 1mm or less.

Ashcat had a good point about ceilings, low ceilings can be bad for OHs and mics being too close to moving cymbals can be bad. I tend to like overheads about 45" from the snare but if the ceilings are low it can be a catch-22.

IME experience if such less than ideal conditions exist, dropping back to something simple like the recorderman mic setup can eliminate a number of the variables. It's sort of a guerilla technique anyway, somewhat designed for such conditions IIRC. It also would likely fit well with the genre/music the OP is recording assuming the drummer is dynamically steady.

[jrk]

Originally Posted by Jack Ruston

In my view, the time aligning thing sounds very un-natural, but each to their own.

But in the particular circumstance described by the OP, time aligning (OH with snare) would make the specific problem go away (probably). If it sounds better, it's worth doing. If it mucks up the room sound too much, then don't do it.

[G-Sun]

The subject is determined by physics and the understanding of waves.

http://jonstinson.com/the-secret-to-...rm-recordings/

[jrk]

Originally Posted by G-Sun

The subject is determined by physics and the understanding of waves.

Isn't it all?

[martifingers]

But do not neglect the power of psychoacoustics... it's not all just waves, it's how we perceive them.

[karbomusic]

Gentle reminder...

I play the two tracks, switch phase on one of them and the snare becomes fatter and punchier.

In the majority of real-world scenarios the engineer moves the mic, places the polarity button in the position that sounds best or aligns the waveforms manually and moves on.

"When you hear hoofbeats, look for horses not zebras".

Just sayin'

[G-Sun]

Originally Posted by jrk

Isn't it all?

That's a materialistic point of view.
Physics is limited to the physical universe
-although every physical law has it's counterpart in other dimensions.

ymmv

[Glennbo]

I've spent the last month playing with the mic positions of my overhead mics on drums. I finally arrived at a position I like which has a pair of AT2020s 9" from each other, and rotated over the kit such that one mic is predominantly over the snare and rack tom, and the other is predominantly over the floor tom. That got rid of lots of phasing I was experiencing but did narrow the stereo spread.

If I look at hits between those two mics now, they are lined up with each other and sound full all by themselves.

That said, I also use spot mics on the kick and snare, and those two mics I hand align every time on every project, and IMHO the end result sounds much more like what I hear in the air with my ears than it does without hand aligning the kick and snare mics to match the overheads.

If I had four ears, with two where they are now and two at my chest or lower, I might have a different opinion about time alignment.

[jrk]

Originally Posted by G-Sun

That's a materialistic point of view.
Physics is limited to the physical universe

As, indeed, am I.
Cheers!

[Tubeguy]

Originally Posted by BigFella

https://www.youtube.com/watch?v=4qgm...ature=youtu.be

The odds for great drum sound seem almost impossible after seeing this, and that's only one mic. There is a Billion variations yet most of us still manage to get a decent sounding drums. That's quiet amazing in it's self.

[numberthirty]

Originally Posted by Tubeguy

Great replies thanks. So basically a comb filtering, it never crossed my mind. I didn't think distance would cause this unless it's stereo mics.
Now I can sleep better knowing what it is.
I normally mic from distance but have close mic on snare for adding punch, this is where the comb filtering happens. Switching phase on the snare mic can make it fatter. But it also depends on how hard I play the snare, not much difference when I play softly.

The 3:1 rule is a thing for a reason.

[ashcat_lt]

Originally Posted by numberthirty

The 3:1 rule is a thing for a reason.

See but that's not actually about distance either. It's about relative volume. I prefer to call it the "at least 9db rule of thumb", and I basically covered it in my reply above.

[karbomusic]

I think we are getting hung up on the the phrase "about distance" - in these cases, the point is that changing distance changes the result, that's all - especially since a different result is the thing desired. I get your academic part, and the OP did ask "why" so there is that. I guess I'm just more hung up on fixing the issue and moving on - much like turning amp SIM knobs till it sounds good vs all the back and forth about -18db and/or gain structure.

[ashcat_lt]

Now who's hung up on language?

So Let me put it another way:

The "3:1 Rule" does not apply in the case of snare and overhead mics. IF it could be done physically it would be undone at the mixing desk.

But what's to fix? OP didn't actually ask for a fix. They know how to deal with. Flip phase til it sounds good. We offered plenty alternatives anyway.

OP asked to understand how and why it happens. It IS kind of basic wave math, like most everything we do. I'm trying hard to explain it in practical terms that might help with understanding rather than clouding it with half-answers and folk lore. What you call pedantic I call precision.

[karbomusic]

Originally Posted by ashcat_lt

Now who's hung up on language?

Well I did leave it open by saying we as in whomever and I'm not faulting you.

OP asked to understand how and why it happens.

Yea, I noted that in my last post too. As I implied, minus the why, we usually agree on the just turn the knobs part so in all honesty, I was promoting that regardless of the ask.

[ashcat_lt]

I mean, I think there's a lot of value in knowing which knob is most likely to give you the result that you want. It's perfectly fine to just do that intuitively without really caring about how the circuit is built, but some of us want to take the thing apart and see how it ticks, and there's nothing wrong with that either. As long as we're actually making the noises that we want to hear at some point along the way, I guess.

[karbomusic]

I agree, there is pretty much nothing my parents got me for Christmas growing up that wasn't in a million pieces two weeks later. Apologies for the derail.

[ashcat_lt]

Coincidentally, today I received the Laser Distance Meter that I ordered mostly to help with placing spaced overheads.

[serr]

Originally Posted by ashcat_lt

Coincidentally, today I received the Laser Distance Meter that I ordered mostly to help with placing spaced overheads.

Someone showed me a measurement tool app on their iPhone the other day that does exactly that. And it appeared to even work! You know, I might actually download that one of these days and actually start using my phone as a little device here and there. (Assuming the cheap android running knockoff my cheap self uses can do similar and someone has ported that app...)

Maybe this "poor man's internet" business with a phone has finally evolved into something useful?

The drummer usually leave some sticks lying on the snare and I'll just use those as a crude measuring stick at present for the overheads.

[karbomusic]

Originally Posted by ashcat_lt

Coincidentally, today I received the Laser Distance Meter that I ordered mostly to help with placing spaced overheads.

Probably better than the string I've been using. Might have to grab one of those.

[Magicbuss]

Originally Posted by karbomusic

That's my opinion as well. My theory is that aligning is trying to account for one misalignment but it's effectively moving every surface reflection in time as well - YMMV on how much that matters - I will post-align a couple of mics on a guitar cab (if needed) while trying to get bot mics at the exact distance but there aren't wall reflections of substance to deal with there. Since I already know where the elements in the mics are, I usually don't have to post-align them anyway as I can usually get them within 1mm or less.

Ashcat had a good point about ceilings, low ceilings can be bad for OHs and mics being too close to moving cymbals can be bad. I tend to like overheads about 45" from the snare but if the ceilings are low it can be a catch-22.

IME experience if such less than ideal conditions exist, dropping back to something simple like the recorderman mic setup can eliminate a number of the variables. It's sort of a guerilla technique anyway, somewhat designed for such conditions IIRC. It also would likely fit well with the genre/music the OP is recording assuming the drummer is dynamically steady.

95% of the time AutoAlign by sound radix makes my drum tracks sound better. Its a magic time saving plugin.

[karbomusic]

Originally Posted by Magicbuss

95% of the time AutoAlign by sound radix makes my drum tracks sound better. Its a magic time saving plugin.

They've always sounded fine just plain mic'd/recorded correctly for me, the few times I aligned just to see, never heard much to get excited over. YMMV.

[Tubeguy]

Originally Posted by Magicbuss

95% of the time AutoAlign by sound radix makes my drum tracks sound better. Its a magic time saving plugin.

I've tried aligning yesterday to see what happens. It turns out that it's useless to me because for some songs I need to flip one of the mics to get the drums to sit better or for an effect. For me it would be one of those things that keeps telling me that I'm doing something wrong when I'm not. But it's good to help understanding how things work in perfect World.

[Judders]

Originally Posted by karbomusic

They've always sounded fine just plain mic'd/recorded correctly for me, the few times I aligned just to see, never heard much to get excited over. YMMV.

It's not something I do, I'm of the "check the mic's and move/flip polarity as necessary" school, but I have heard professional engineers swear by Sound Radix (I guess it becomes a lot more useful when you're mixing drums you didn't record yourself). It gives you a number of options of alignment, so it's not like it's trying to take away all the time differences of overheads and room mic's, it just gives you a range of alignments to choose from so that comb filtering is minimised.