Drum phase prevention and fixing.

J

jasonwick

New member
So there is loads of great advice on here about preventing and fixing mic phase issues. I have much more of an understanding than I did a week ago.
I no longer get phase issues with my top/bottom snare mic, same goes for my overheads but should i be thinking about phase issues between my overhead and room mics or any other combination??

also I recently noticed some of my XLRS are wired in reverse!! surely this will cancel any good phase prevention work I do!!!!
Thanks
 
Are you talking about phase or polarity, or both?

If your XLR cables are wired 2-3 and 3-2 then you'll have inverted polarity.
I'd fix them, or mark all the 'wrong' ones so you know to flip it back in your DAW.

As far as phase between overheads and room mics, I don't know that you'd want to fix it.
I hear about guys lining files up in the daw to compensate for time/distance delay, but I never saw the point.
Surely that's what a room mic is for, right?
I always figured that even if you line up the transients, there will still be issues due to the mics picking up room reflections at different times. Maybe I'm wrong about that?

Apologies if you already know this, but:
Two recorded waves out of phase start at different times.
Two recorded waves of opposite polarity start at the same time.


Hope some of that's useful.
 
Thanks... thats great..

ok so obviously some info needs to be sorted in my head a little concerning polarity and phase!
So regarding overheads and rooms mics and leaving them as they are....would the same be said for overheads and say snare mics??
so I should really only worry about phase issues on and when......using two snare mics, if using two kick mics , if using two room mics and the on the overheads...phase issues between these sets are ignored???


and...
""two recorded waves of opposite polarity start at same time"" ---- how would this effect the recorded sound??
 
jasonwick said:
so I should really only worry about phase issues on and when......using two snare mics, if using two kick mics
Click to expand...
You won't have phase issues with two snare mics (top and bottom), unless they are different distances from the drum.
They'll have opposite polarity though, so invert one of them, preferably the bottom one.



jasonwick said:
""two recorded waves of opposite polarity start at same time"" ---- how would this effect the recorded sound??
Click to expand...


Picture it as two sine waves for simplicity....you know...S on it's side.

So, one S starts at zero and the curve goes upwards.
The inverted version starts at zero and the curve goes downwards.
At any given point, the sum of their values is zero.

They start at the same time, but are the symmetrical opposite of each other when viewed as a wave.
Two sines 180degrees apart will completely cancel.
Your snare/kick wont completely cancel because there are real world variables like the room reflections etc, but they will partially cancel.







With the room/OH mics, other guys might have different ideas, but I'd say forget it.
Get the polarity right if you're using top and bottom snare, or front and back kick mics.
Other than that, Keep it real.

We once had a tutor who got us to realign the recorded overhead tracks so that their transients matched with the close kick/snare.
Now I'll admit, It did create a bit more punch, but
1: it was negligible
2: it wasn't natural
It might be something you wana play with and make your own decision?
 
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Check this out.
Definitely needs to be a sticky.

Also, you might want to pay attention to the placement of the two overhead mics.
You should hear a big difference if you make sure that they are equidistant from the snare, kick, or both.

Use a piece of string or a cable from the centre of the snare to measure up to each overhead.

Sure, there'll be a phase discrepancy between snare mic and overheads, but there wont be an extra problem between the two overheads.
 
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Let's not forget that phase relationship - as nebulous as it is - is a huge part of the psychoacoustic response of the ear/brain. It's the difference in arrival times of two similar waveforms at the ear that determines how the brain perceives positional cues. This is, at the root, all due to our keen survival and evolution of our species. Many experts claim it was necessary when hunting to safeguard from being hunted.

But I digress.

Phase (and often polarity as well) is also a great tonal manipulation tool. Comb filters are fun, right?

As far as drums go, I'd say it's good to try flipping the polarity on every track on the drum kit in different combinations to see if it improves the situation and gets you closer to your goal sound. I can't tell you what a major difference it can make and is the number one secret magic silver bullet, if there ever was one.

There are other ways to get an idea of what to do though...

I probably shouldn't be advocating anything visual, but if you zoom in far enough you can actually see pretty obviously when two waveforms are opposite in polarity. But which one do you flip? Well, I always choose to flip the negative-going waveform because I am looking for a positive excursion at the speaker first. I want the speaker to push out air at the initial transient, not pull air in. Remember that all waveforms are analogous to voltage and therefore are almost exact facsimiles of the movement of the speaker, right? Think about what will happen if a negative-going waveform on say, the kick drum, has to contend at the exact same time with a positive-going waveform of, say, the bass or some other transient heavy instrument. The speaker will not perform well at all.

Get what I mean?

Oh, and on the topic of clownfucking your way into "time-aligning" and all that "lining up" garbage; it's is a complete waste of time. And I'm not talking about quantizing, I'm talking about lining up track to track. It's just not humanly possible to do with any sort of precision on an acoustic drum set. No one yet has figured out a way to get 0% bleed between multiple mikes so any change you make to the intrinsic timing between tracks is going to produce ill-effects such as comb filtering and huge tonal shifts.

Anyway. Rant over.

Cheers :)
 
Steenamaroo said:
You won't have phase issues with two snare mics (top and bottom), unless they are different distances from the drum.
They'll have opposite polarity though, so invert one of them, preferably the bottom one.
Click to expand...

They are different distances from the top head which is where the sound originates, so they are out of phase and opposite polarity at the same time. Fortunately the bottom head filters the sound so much and the snares add so much more sound that there is often too little coherence between them for phase or polarity to matter. Inverting the bottom mic sounds different but not always better.
 
Mo Facta said:
But which one do you flip? Well, I always choose to flip the negative-going waveform because I am looking for a positive excursion at the speaker first.
Click to expand...

Of course the drummer hears his kick, snare and toms from the beater side which means the initial transient is negative pressure. So who is right? Doesn't matter. Make it sound good. But I also tend to go for positive initial transients.

Mo Facta said:
Oh, and on the topic of clownfucking your way into "time-aligning" and all that "lining up" garbage; it's is a complete waste of time. And I'm not talking about quantizing, I'm talking about lining up track to track. It's just not humanly possible to do with any sort of precision on an acoustic drum set. No one yet has figured out a way to get 0% bleed between multiple mikes so any change you make to the intrinsic timing between tracks is going to produce ill-effects such as comb filtering and huge tonal shifts.
Click to expand...

There is comb filtering with or without time alignment. Whether it sounds better to align things depends largely on how the kit it miced. With spaced overheads there is no common reference point to align to so it's futile. With a coincident pair or single overhead there is a common reference point so it can be done. It's not about getting zero bleed, it's about correcting the worst of the phase misalignment which is going to be between each close mic and the overheads. It can significantly, even drastically, tighten up the sound. And if it doesn't it can be undone.

Whether it should be done is a matter for people do decide for themselves. Your opinion says more about the limits of your knowledge than it does about drum mixing.
 
bouldersoundguy said:
They are different distances from the top head which is where the sound originates, so they are out of phase and opposite polarity at the same time. Fortunately the bottom head filters the sound so much and the snares add so much more sound that there is often too little coherence between them for phase or polarity to matter. Inverting the bottom mic sounds different but not always better.
Click to expand...

While you're right, I very much doubt that OP had taken that into account.

I'm just trying to make the difference between phase and polarity apparent, but OP, if you were already taking BSGs point into account, Apologies. :) I underestimated you.
 
ok great lots of good stuff there for me to unravel and understand ;)
Its all falling into place..
Thinking out loud..so Phase and polarity although different are very related in that they describe different states of two sound waves and there interaction..I get the difference.

Still some confusion -
1. So two mics equally spaced from sound source would have no polarity or phase issues, and visually the waves would rise and fall together. (or using the 1/3 rule would also produce this alignment.)
2. Two mics not quite equally spaced could be out of phase and visually the waves would start and finish at slightly different times.
3.Two mics again not equally spaced could have the effect of reverse polarity if the mics were spaced just so to create 180 degrees phase misalignment, although if mics were not equally spaced for them to be completely reversed would be as unlikely as the mics being completely in phase.

are the statements above correct?? or am i still waaaay out!
and... if they are correct why do some of the comments above say that the top and bottom mics of a snare will have reversed polarity??

Im getting there!?!?!
Thanks again for great help
 
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and further to this..
Excepting firstly that reverse polarity signals start and finish at the same time where as out of 180 degrees out of phase signals do not, are they otherwise the same thing? :facepalm:
 
jasonwick said:
1. So two mics equally spaced from sound source would have no polarity or phase issues, and visually the waves would rise and fall together. (or using the 1/3 rule would also produce this alignment.)
2. Two mics not quite equally spaced could be out of phase and visually the waves would start and finish at slightly different times.
3.Two mics again not equally spaced could have the effect of reverse polarity if the mics were spaced just so to create 180 degrees phase misalignment, although if mics were not equally spaced for them to be completely reversed would be as unlikely as the mics being completely in phase.
Click to expand...

You're more or less there but there are a few mistakes.
Point three is wrong because polarity inversion isn't related to time/distance.
(edit. Didn't see your other post)

Simply, two mics on different sides of a sound source and facing the sound source will have inverted polarity (theoretically).
Sound reaches them at the same time, but with opposite effect.


Two mics at different distances from a source, in the same direction, will only have a phase discrepancy.


As BSG pointed out, acoustic recordings will never have perfect opposite polarity for a whole number of reasons, but that's the basic idea.
 
jasonwick said:
and further to this..
Excepting firstly that reverse polarity signals start and finish at the same time where as out of 180 degrees out of phase signals do not, are they otherwise the same thing? :facepalm:
Click to expand...

No. They only appear to be similar in textbooks where a uniform wave is used as an example.
A sine wave is identical cycle after cycle so 180degree phase and inverted polarity look the same after the first half cycle.
Your real acoustic recordings aren't uniform like that though. The waveform is constantly changing.


Btw, the 1/3 rule; I don't think that's what it means.
If you keep one mic a foot from a source and keep moving the other one back for ages, there's a point where it just becomes an echo right?
I think the 1/3 rule is more of a point at which the phase issues are less obvious, or destructive, but it doesn't fix or align anything.

I'll look into that. I know it's heavily debated and imagine someone will clear it up shortly.
 
jasonwick said:
and further to this..
Excepting firstly that reverse polarity signals start and finish at the same time where as out of 180 degrees out of phase signals do not, are they otherwise the same thing? :facepalm:
Click to expand...

No. They only appear to be similar in textbooks where a uniform wave is used as an example.
A sine wave is identical cycle after cycle, but your real acoustic recordings are not.


Btw, the 1/3 rule; I don't think that's what it means.
If you keep one mic a foot from a source and keep moving the other one back for ages, there's a point where it just becomes an echo right?
I think the 1/3 rule is more of a point at which the phase issues are less obvious, or destructive.


Guys, If I'm screwing anything up here, jump in. :)
 
The 3 to 1 rule only applies to multiple sources, not to multiple mics on one source.
 
Haha, good to know either way man.

Ok, i get that two sources, each with a mic at one foot distance. You'd want the two mics at least 3 feet apart then. That's cool.

Out of interest, would it still apply with single source? Would you observe it with a 57 on a cab and a condenser further back, for example?
 
Steenamaroo said:
Out of interest, would it still apply with single source? Would you observe it with a 57 on a cab and a condenser further back, for example?
Click to expand...
I don't know for sure, but I don't think so. The distances would probably depend on the mics, etc....For that matter, the 3 to 1 rule is probably dependant on what types of mics, etc...also. So, I'm pretty sure "3 to 1" is a general guideline-safeguard, and not a definite rule.
 
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