Bottom Snare Mic

A

AlexW

New member
I typically use a bottom snare mic (dynamic pointed at the kick beater). Lately I've been using an SM7. In any case, I've always flipped the phase with the top snare mic; but on a session I'm working on now, flipping the phase made the kick disappear. I haven't had it happen before, but could just be the way the mics were positioned on this particular kit I guess. Anyone have a similar experience or thoughts?
 
Another potential suspect is that although you thought you were inverting phase on the bottom mic, you were in actuality setting it for the same phase as the top signal. This could be because the top mic already had it's phase inverted somewhere in the signal chain, or it could likely be that on one of the microphone signal paths the phase is getting errneously inverted by crossed wiring in a cable plug or an instrument or patch bay jack.

G.
 
Certainly possible. In any case, not flipping the phase on that mic gives a better overall sound, so I'll just stick with that.
 
The other possibility is the lead could have been wired upside down eg: hot to pin three, cold to pin two and screen to one.
 
Yeah, I think that was what Glen was alluding to. I'll double check the cables but sort of doubtful that's the cause.

I guess a more general question is that with a top and bottom mic, will they always be presumed to be 180 deg. out of phase, or is this just an approximation? What's causing the phase cancellation in this case? Is it the time gap between sounds hitting the different mics? With a DAW editor, could you theoretically correct the phase relationships visually? And in a case such as this, where the mic is picking up both the snare and the kick, what controls?
 
From what I understand, phasing is just that the signal is upside down (think of in an editor looking at waveforms). I would think it's possible to invert the signal in a DAW or music program. I'm just learning about this myself.
 
Yeah, that's what I was alluding to, but also saying that it could happen anywhere along the signal chain.

The phase reversal between the bottom and top of the drum has to do with the actual physical air/drum skin travel direction. From the top of the drum, when you hit the skin, the skin is being bent down; away from the top-mounted microphone, yielding an attack waveform that begins traveling negative. That same drum hit as seen from the bottom sees the bottom side of the skin pushing towards the bottom-mounted microphone, causing the initial attack of the wavefrom to go positive; a mirror image waveform results.

There is not so much a phase shift happening as there is a phase inversion. Yes a phase shift of 180 degrees is identical to a phase inversion, but an inversion is the actual action happening here; there is not a phase shift due to time delay causing a 180 degree shift, instead there is an inversion caused by the fact that the two microphones are looking at mirror images of the same physical action. To be technical, there is some tiny phase shift as well, because of the extremely short amount of time it takes for the sound to move the few inches from the top of the drum to the bottom, but that tiny shift is unrelated to the actual inversion.

HTH,

G.
 
SouthSIDE Glen said:
Yes a phase shift of 180 degrees is identical to a phase inversion, but an inversion is the actual action happening here
Click to expand...
That would only be true of a perfectly symetrical wave like a sin wave.
As an example; take a wave and then take a copy of that wave and invert it. Play them at the same time and you get no sound at all. But take a copy of the original wave and move 180 degrees forward and you get a phaseing sound when played with the original wave.
 
ecktronic said:
That would only be true of a perfectly symetrical wave like a sin wave.
As an example; take a wave and then take a copy of that wave and invert it. Play them at the same time and you get no sound at all. But take a copy of the original wave and move 180 degrees forward and you get a phaseing sound when played with the original wave.
Click to expand...
Yeah, that's both true and a good point. Nice catch. :)

And to take that even further, there really is no true measurement of shift by degrees on an irregular waveform of varying wavelengths. One would have to arbitrarily select a "base wavelength" to use as the measurement.

G.
 
SouthSIDE Glen said:
Yeah, that's both true and a good point. Nice catch. :)

And to take that even further, there really is no true measurement of shift by degrees on an irregular waveform of varying wavelengths. One would have to arbitrarily select a "base wavelength" to use as the measurement.

G.
Click to expand...
Soo true Glen. I was just using the cross over points which is totally wrong.
 
Phase "invertion" or "flipping" is not the signal upside down. Phase invertion DOES NOT exist. You should understand the differance between phase and polarity.
It seems like a stupid matter of terminology but it's not ...

In reallife audio there is no such thing as phase inverting. You can SHIFT phase on a certain frequency but this is a whole other story. In a one frequency signal (eg. a sine) a phase shift of 180° has the same results as inverting polarty. Phase is merely a time based aspect expressed in °
You cannot "invert" seconds or minutes either.

Now inverting polarity (cold<->warm) is a method used to compensate for time differences caused by the different dinsances from mikes to their source or to to prevent fequency cancelling caused by mics that are oposite (eg top/bottom mikes). And SOMETIMES it might work.

This whole phase theory is way too complicated so it's best not to confuse the terms, you'll only make it worse....


Now back to your question :D

"dynamic pointed at the kick beater" ... as in the rear of the microphone pointed at the kick? Otherwise it's quite logic that your snare sounds better polarity inverted, and that it cancells the kick.

Just try to get the best sound. No matter if you invert polartiy or not. Just make sure you check the interaction with other mics (eg. kick, OH's etc...)

greets, arno
 
Wait, you lost me. Did the kick disappear, or the snare?

If the kick disappeared, hit the phase switch on the kick mic. That way you can still have the proper phase relationship between the top and bottom snare mics.
 
Thanks for that Arno, good stuff. And the dynamic (Shure SM7) was pointed at the kick beater; I'd say the head of it was roughly just beneath the shell of the snare closest to the kick--8 - 12 inches away from the beater. I've done this before with a different dynamic mic (Beyerdynamic Soundstar) and not had the cancellation issue.
 
Farview said:
Wait, you lost me. Did the kick disappear, or the snare?

If the kick disappeared, hit the phase switch on the kick mic. That way you can still have the proper phase relationship between the top and bottom snare mics.
Click to expand...

Yep, the kick disappeared--that's an excellent thought. I'll play around with it some more tonight and see what works out the best. It's a session with around 7 songs altogether. I'd flipped the phase on the bottom snare mic on a couple of the tracks but hadn't gotten around to doing it to all of them before burning a rough mix--that's where I really noticed the difference.
 
You must have accidently had the kick drum mic the same distance from the kick head as the bottom snare mic. (just on opposite sides) If for some reason the kick doesn't sound as good that way, put the polarity of the kick and bottom snare mic back and flip the top snare mics polarity.
 
Yep, I'm looking forward to getting home to play with it some this evening. Thanks for the suggestions.
 
Yeah but maybe inverting polarity on snare's top mike might cancell out with the overheads. I'm not sure, but you should try it it anyway. Are you doing this while mixing or tracking ? Either way, make sure you take note of every track wheter it's inverted or not.

This will keep you from a headache in the future...

-arno
 
I'm doing the inversions at this point during mixing in Protools LE. The inverted waves are marked as such, so it's easy to keep track of them; and I do the inversions on a duplicate wave file so I can easily switch back to the original.
 
You must log in or register to reply here.
Back
Top