Phase reversing, is it essential?

[billiamwalker]

For the longest time i've been recording top and bottom snare. Some of you will understand that it is highly recommended in rock music for reason such as build ups and what not. Do i need to reverse the phase of the bottom mic (which was told to me by a guy at guitar center who doesn't really understand engineering all too well. he just knows what he's read in a do it yourself recording website.) I've reversed teh phase digitally in the mix and haven't really noticed any difference.

Would it make a huge difference to my snare quality and do i need a preamp with phase reverse to get the full effect instead of changing it in the mix.

Also i've heard about actual mic cables that can do the same. Is this true and where can i find them?

Thanks for your help guys,
-Billy
(aspiring engineer)

[bap]

I have only done 'minimal' drumset micing - usually 4 mics maximum. If things need to be 'fixed' you can often correct it with mic placement.

I have PhaseTone [TritoneDigital] and sometimes fart around with phase/delay settings but would never switch phase going in just because some guy at G.C. said it was the thing to do.

[billiamwalker]

i understand where you're coming from and i'm definatly not going to take the guitar center's advice since they only know so much.

I record rock bands. In rock music the drums are very important in the mix. Mainly i'm just trying to improve my snare sound.

So the question still stands, should i get a phase reverse through a preamp or am i still ok where i stand without having to switch anything or flip the phase in the mix.

If anyone is reading this... i can pull up some samples and let yall hear it to see if initially i was running into phase problems with my snare.

[mjau]

So the question still stands, should i get a phase reverse through a preamp or am i still ok where i stand without having to switch anything or flip the phase in the mix.

Not to sound purely cavalier about this, but does it sound better when you flip polarity, or does it sound worse? Check with all your drum mics going - not just the snare mics on solo.

[billiamwalker]

so you mean the phase of all the mics? possibly all my mics are out of phase causing more damage to my snare?

sort of out of the loop as of now.

and no.. insult me at all possible costs. and i'm not being sarcastic. this is stuff i need to know. aka constructive criticism.

so if i sound totally stupid on this topic right now..it's because i am.

[mjau]

No worries...I mean just flip the polarity of the bottom mic, listen how the whole kit sounds (i.e., all the drum mics together), and the then flip the bottom snare mic's polarity back and compare that sound. If one sounds significantly better than the other, go with it. If you're working with a DAW, you can probably flip the polarity back and forth within your program.

[FailedSitcom]

If you're using a DAW, you could also record the snare being hit and see just how much phase cancelation* there is in a sequencer/wave editor. Even then, it's how it sounds to you that should determine your final decision.

The best way I can explain this is with numbers I'm afraid. Think of the top of the snare being +7 and the bottom being -5.5, when these opposite phases are combined they can make each other noticeably quieter. That's how I understand it at least.

[billiamwalker]

The best way I can explain this is with numbers I'm afraid. Think of the top of the snare being +7 and the bottom being -5.5, when these opposite phases are combined they can make each other noticeably quieter. That's how I understand it at least.

Ok, that's all i need. That seems like the best way to check and make sure i'm doing everything right. I'll def. take all of the others into consideration...but this one seems like the best method.

But one question... will the actual decibles showing up of the two signals actaully get quieter? ex. - if i'm at +7 and -5.5 and turn on the bottom mic... will the actual signal fall down or will it merely SOUND quieter?

[ryanlikestorock]

If the sum of the two signals is less than either signal on its own, you should probably invert the phase of the bottom mic.

[JGriffin]

The best way I can explain this is with numbers I'm afraid. Think of the top of the snare being +7 and the bottom being -5.5, when these opposite phases are combined they can make each other noticeably quieter. That's how I understand it at least.

Ok, that's all i need. That seems like the best way to check and make sure i'm doing everything right. I'll def. take all of the others into consideration...but this one seems like the best method.

But one question... will the actual decibles showing up of the two signals actaully get quieter? ex. - if i'm at +7 and -5.5 and turn on the bottom mic... will the actual signal fall down or will it merely SOUND quieter?

This is the reason for the phase flip--with top and bottom snare mikes you have the same impulse traveling in two different directions, which will result in cancellation, a collapsing of the waveform--yes, the signal will "fall down" and it will sound quieter...or just cancel at certain frequencies and sound different, possibly worse.

[theBaldfather]

I have rarely found a time when I didn't need to reverse the phase on the bottom mic. I usually zoom in on my daw and just look at alignment. If it is out of phase in the first few wavelengths, I'll flip it and listen. In phase mics tend to have a fuller bass response, and better stereo imaging. With kickdrum it's usually the same way if you have room mics. Out of phase room mics will have an sound that makes the kick sound like it is coming out of each speaker individually as opposed to coming from the center. That was a tough thing for me to learn to hear at the beginning. Hope that helps a little. I'm still learning all the tricks myself.

[Professor]

I think it's important here to take a moment and consider the concept of "absolute phase".
A lot of people claim that we can't hear differences in absolute phase, and indeed with sustained, pitched sounds that is generally the case. Percussive sounds, however, with fast attacks and quick decays can certainly expose problems in absolute phase.
Consider a strong bass drum hit from a typical drumset bass drum with maybe a blanket or pillow in there to dampen the sustain (accelerate the decay). If you are standing in front of the drum, the first wave-front arriving at your position is a "push" of air, an increasing air pressure, a 'compression wave', which at the microphone should be translated into a positive voltage. That voltage should stay positive all the way through recordinng and playback so that when the speakers playback that impact, the first impulse you receive is a "push" of air from the speaker cone.
Of course, after that initial attack, the drum head must recover, so it pulls back and "sucks" the air away creating a 'rarefaction wave' which should be captured at the microphone as a negative voltage and subsequently delivered as a negative voltage to the speaker so the driver pulls back as well. The head will resonate a bit after that, creating additional positive and negative wave fronts until the sound completely decays, but none of the waves will be as strong (loud) as the initial attack.

OK, bass drum is relatively easy to picture. But doesn't the same thing happen at the snare drum? The drumstick strikes and rebounds off the drum head, and the initial impulse is a "push" of air out the bottom of the drum. A microphone under the drum would transduce this acoustic pressure wave into a positive voltage. But a microphone above the drum will see the drumhead moving away and "sucking" air away from the diaphragm and so the top snare mic will transduce that pressure into a negative voltage.
Which microphone is 'out of phase' relative to nature?
Well the top one of course. And the same thing happens with toms and often with cymbals when the overhead mics are above the drummer's side of the cymbals.
So I will generally invert the overhead, snare and tom mics, not the kick, and while I never really use an 'under-snare' mic, I would consider that mic to be phase-correct. Of course, I also like to time align the close mics to match the most distant mics (overheads in my case since I don't often use room mics). Now certain placements can screw with this, and some microphone types are not quick enough to catch that first attack very strong at all, but that's the theory behind what's going on, or at least what should be going on.
If you're working on a DAW, then find an isolated snare hit (where other instruments like cymbals and kick aren't playing) and zoom in on the first impulse of the wave. That will show you which mics are delivering positive wave fronts and how far apart the impulses are in time so you know the delay between snare & OH, etc.
Now as to whether you should invert at the preamp or in the box, that doesn't matter so much. Once it's voltage, it's voltage, so you can flip it anywhere you like. I don't like the idea of using inverting mic cables unless you have them very clearly marked (like a different color cable) so you don't use them in the wrong place on other sessions.

-Jeremy

[billiamwalker]

Jeremy, i'd just like to say you're being of alot of help on all of my threads.


When i go back to the studio and i'm going to start inverting the overheads, top snare, and toms of some projects and see how it turns out.

Thanks alot!

[Mark Alan Miller]

Checking polarity is always a good idea in multiple micing situations.
Due to phase issues caused by arrival time differences (i.e. OHs vs Kick), or polarity issues by two mics on the same source (both on the snare, for example), looking at polarity is key to finding out if it's a simple way to make something sound better. I always look at OHs vs Kick and OHs vs Snare, and hope that if I need to flip polarity for the sake of the K that the Snare won't suffer... if so, mic position might need to be examined, etc etc. This of course, is assuming that things aren't sounding great. If they're sounding great, it's time to press 'record'.

I can't add much more than what the good Professor already said, but I wanna say (didn't see it mentioned but might have missed it) that when flipping the polarity of a signal, please refer to it as that, polarity. So, the little button on the preamp? It's a polarity button. Just a little something that bugs me. Sorry to nit-pick.

On that note, though, you can make any mic cable (or TRS patch cable) a polarity flip cable by swapping the connections on one end between pins 2 and 3 (XLR) or between the tip and ring (TRS). Make sure you clearly label such a cable so you'll know what you're doing when you use it, and not use it by accident.

[billiamwalker]

I can't add much more than what the good Professor already said, but I wanna say (didn't see it mentioned but might have missed it) that when flipping the polarity of a signal, please refer to it as that, polarity. So, the little button on the preamp? It's a polarity button. Just a little something that bugs me. Sorry to nit-pick.

I totally understand, this stuff would be tons easier if more people were politically correct.

Thanks for the extra info Mark!