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phlopip
New member
Can someon explain it and how to recitfy it. thanks
Farview
Well-known member
Are you having a problem with it?
It's a lot easier to explain in context. It's a simple concept, but it's easy to get confused because different things happen in different situations.
Most of the time, it is caused by a difference between the time a sound reaches one mic and another. When the signal from the two mics are played back, the timing difference causes comb filtering. Kind of like what a flanger does.
The simplest way to fix this problem is by having the mics the same distance from the source of the sound. Another way is to line up the waveforms of the two mics in the DAW once they are recorded.
It's a lot easier to explain in context. It's a simple concept, but it's easy to get confused because different things happen in different situations.
Most of the time, it is caused by a difference between the time a sound reaches one mic and another. When the signal from the two mics are played back, the timing difference causes comb filtering. Kind of like what a flanger does.
The simplest way to fix this problem is by having the mics the same distance from the source of the sound. Another way is to line up the waveforms of the two mics in the DAW once they are recorded.
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phlopip
New member
like in terms of recording a drum kit. i hear the term phasing thrown around alot but i'm not sure what it means and how it can be fixed.
Farview
Well-known member
The easiest one to explain is the top and bottom snare micing.
If you mic both the top and the bottom of the snare, you have to flip the phase (polarity actually) of the bottom mic. This is because when you hit the snare, the top head is being pushed away from the top mic but the bottom head is being pushed towards the bottom mic. So the signal coming out of the mics will be going the opposite direction. When you play them back together, they will partially cancel each other out. In the case of the snare drum, the low end will be what gets cancelled. This leaves you with a thin sound.
With the drum kit as a whole, you have a bunch of mics capturing the set. The sound of the snare will reach the mic on tom 1 at a different time than it reaches the snare mic, or the mic for tom 2, or the overhead, etc... Sometimes those sounds arriving at different mics at different times cause cancellation.
Normally, you can just move a mic a little bit to fix it. It also helps when the drummer plays with proper dynamics. The big problem is when the drummer beats the crap out of the snare and lightly taps the toms. This causes you to crank the gain on the toms, which makes the snare drum louder in those mics than it should be.
If you mic both the top and the bottom of the snare, you have to flip the phase (polarity actually) of the bottom mic. This is because when you hit the snare, the top head is being pushed away from the top mic but the bottom head is being pushed towards the bottom mic. So the signal coming out of the mics will be going the opposite direction. When you play them back together, they will partially cancel each other out. In the case of the snare drum, the low end will be what gets cancelled. This leaves you with a thin sound.
With the drum kit as a whole, you have a bunch of mics capturing the set. The sound of the snare will reach the mic on tom 1 at a different time than it reaches the snare mic, or the mic for tom 2, or the overhead, etc... Sometimes those sounds arriving at different mics at different times cause cancellation.
Normally, you can just move a mic a little bit to fix it. It also helps when the drummer plays with proper dynamics. The big problem is when the drummer beats the crap out of the snare and lightly taps the toms. This causes you to crank the gain on the toms, which makes the snare drum louder in those mics than it should be.
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phlopip
New member
thanks that really helped. when you said about changing the "polarity", how do you do that. i'm really sorry but i'm new to this.
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Chibi Nappa
New member
You can change the phase either with a phase flip button on your console or software, or by dissasembling one of your mic cords and wireing it out of phase.
Most people just use the phase button on the console or software.
I guess I should bring up the 3:1 rule. You won't have phase problems if you keep your mics 3 times farther apart than the distance from the sound source. If your mics are 1 foot away from the source, they are at least 3 feet apart. If the mics are 2 feet away from the source, they are at least 6 feet apart. etc.
There are ways to minimize phasing while breaking this rule. X-Y stereo micing for one. Sometimes you have to break the 3:1 rule if you're really stuffing mics around a drum kit. In that case, you really have to learn the sound of phasing and move the mics while listening to all other mics in head phones until you hit the safe spot.
Most people just use the phase button on the console or software.
I guess I should bring up the 3:1 rule. You won't have phase problems if you keep your mics 3 times farther apart than the distance from the sound source. If your mics are 1 foot away from the source, they are at least 3 feet apart. If the mics are 2 feet away from the source, they are at least 6 feet apart. etc.
There are ways to minimize phasing while breaking this rule. X-Y stereo micing for one. Sometimes you have to break the 3:1 rule if you're really stuffing mics around a drum kit. In that case, you really have to learn the sound of phasing and move the mics while listening to all other mics in head phones until you hit the safe spot.
dkelley
Active member
hey, by the way, I just wanted to point out that if you do the math , assuming the recorded source is a point source, then you can never quite match the 3:1 rule in perfect dimensions.
you can't have two mics each 1 foot from the same point source while being 3 feet apart.
they would be 2 feet apart at most if they were facing at 180 degrees (which would be an unusual extreme).So something's up in your description of how to avoid phase cancellation between 2 mics on the same source Nappa.
either that or my math is wrong.
I don't recall the specs right now myself, I just solve phase issues with my ears and verify and fine tune it with the waveforms in the daw after, but there IS some type of rule like what you described. I just don't see how that particular math could be correct.
I don't think you could have a 3:1 rule for 2 mics on the same point source. if you have 2 mics that are 2 feet each from the same source, how can you have the mics 6 feet apart? it'll be 4 feet apart at most, probably much less. so there will be phase issues.
I'm an experienced engineer, but this point is messing with my head LoL
Cheers,
Don
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Chibi Nappa
New member
I wasn't very clear. You base it from the closer mic. If the closest mic is 1 foot away from the source, the other mic is 3 feet away from the first mic.
Farview
Well-known member
The second mic needs to be AT LEAST 3 times further BACK from the first mic. This only works because of the volume difference between the close mic and the far mic. If you turn the distant mic up to the same level as the close mic, you will still have phase problems.
The 3 to 1 rule has nothing to do with stereo micing. Actually it is a method to reduce bleed when micing two different things in the same room.
It can be applied to a drum kit easily. If you have a tom mic 1 inch from the tom 1, the mic for tom 2 needs to be at least 3 inches from tom 1 and so on.
http://www.recordingeq.com/articles/321eq.html
The 3 to 1 rule has nothing to do with stereo micing. Actually it is a method to reduce bleed when micing two different things in the same room.
It can be applied to a drum kit easily. If you have a tom mic 1 inch from the tom 1, the mic for tom 2 needs to be at least 3 inches from tom 1 and so on.
http://www.recordingeq.com/articles/321eq.html
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mixsit
Well-known member
Yeah!!!
Yes, and it has even less to do with near/far mics on the same source, for the reason Farview mentioned.Gee-adds. So much kungfoosion around 3:1'.
If you teach about this ratio thing, the distance but not about the attenuation which is what it is about.. shit happens. (Apparently!
Farview
Well-known member
The other thing that I forgot to point out is that you can have two mics any distance away from a source, as long as one is 9db quieter than the other, you won't have any phase problems.
