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  Audio Waveform Polarity

Don't let anyone tell you that polarity doesn't change the sound. It does. If you "visualize" the sound coming out of your speakers -- imagine whether the attack seems to pull first or push. I know. We're getting into wild stuff here. Electronically, gear doesn't care if the polarity is reversed. It acts the same.  But your ears react differently to the sound when it's contrary to nature. I know, some musicians are contrary to nature and they are way cool anyway!

Where it can really count: Imagine that your kic drum is out of polarity and it's pulling on the initial attack. Now imagine that your bass is polarity correct and the initial punch of the bass is pushing. Your kic is pulling and your bass is pushing. How's that for not really helping create coherent punch!!!!  Want to create more complex waveforms that are harder to "decipher" or figure out why the sound isn't as muscular as the big name recordings? Oh, and out of polarity cymbals sound more harsh than if they're correct. Same with guitars and vocals. 

Surprise: Be sure that your bounced mix and/ or Separations are polarity correct too. This means if you look at your kic drum and the polarity is correct (waveform goes up before it goes down) -- load your mixdowns and Separations into a new session and check to be sure that the kic is going the same way. We have seen some files where the bounces are polarity reversed from the mixdown in the session. We have also seen sampled drums that didn't have the correct polarity.

Kic drum that is polarity-correct
This kic is correct - the leading edge goes up first before going down.

Snare drum that is out-of-polarity
This snare is incorrect (unless you like the sound, but be careful that this isn't occurring at the same time as another track that is correct. They will counter-act each other and lessen the punch.

Cymbal that is polarity-correct
This cymbal hit is correct.

Bass that is out-of-polarity
This bass track is out-of-polarity.

What to do: Insert a plugin to correct the track's polarity. It may be called "Invert Phase" - and relative to another track, yes you could call it phase. But relative to itself (absolute) the concern is polarity.

Head off the problem in the tracking studio:
check the phase/polarity of every wire, mic pre, patch point, input into your recording system, etc.

• Take a pair of drum sticks and click them together in front of a particular mic. Note what cable, what input, etc. Record the click into your system. Look at the waveform. If the click starts up before it goes down, you're good! If not, something in that signal path is flipping the ... phase/polarity.

• Slap the bass! Plug in the bass into every bass/keyboard DI (one at a time) and smack the strings... within reason. Record the smack into your system. If the leading edge of the waveform looks like the one in purple above.... not good. If the leading edge goes up first... you're good!

• Same thing for any guitar "pods" or keyboards. Any sharp percussive sound will do the trick. A vocal or gradual strum of a guitar... not as easy to see what's going on.

Tip: Purchase a polarity checker hardware box like this one - Erik Zobler has one so we should all have one!

Q: If a drum has the mic mounted on top would the signal not go down first due to the drop in pressure from the head moving away from the mic? - Mike

Yes! Glad you asked.

Looking in "slow motion" we could say that the stick does force the top head down first. Responding to the air pressure from the top head, the bottom head simultaneously goes toward the floor in a positive excursion. So the decision, when using 2 mics, about reversing polarity on one of those snare mics would be determined by the preferred sound, especially in combination with the overheads, toms, etc. (Read Secret #3 about overhead phase solutions relative to the snare.)

Your question applies to toms too. I never liked miking the bottom of a tom, but listeners in the audience hear the positive excursion more than the top surface the drummer hears. From the listener's perspective out in the audience (or the room mic's perspective), the question would be which part is heard dominantly. We're probably nit-picking, but what the heck. Oh then there's miking the front of the kic vs. miking the kic head on the beater side....

Here's how it all plays out in my mastering room. When I separate any drums and set the polarity for all positive, it sounds punchier. From the aspect of a close mic on the top of the snare, that's not natural. But neither is compression. No snare drum in nature is compressed, unless done over an electronic system.

Setting the polarity to positive sounds better in my opinion in most cases. The listener's speakers push before they pull when the drum is struck. If that's more polarity-consistent electronically-acoustically with bass etc., despite being less natural, then there's a case to consider the polarity aspect of the drums.

For SURE, a kic drum sounds better pushing, not pulling. Given that most kic's are miked from the front, we're comfortable with that sound. If it's also more polarity-aligned with the bass, there's probably good reason for our preference in this area.

What I'm offering may be a way to look at the snare and toms in a similar way to the way we look at the kic - but simply using an electronic tool to accomplish that result - the polarity plug in (or the console/mic pre phase reverse button). 

Created 02/11/11 - Updated 12-16-11
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Read JV's interview with mastering
legend, Stephen Marcussen in the
May 2003 issue of
EQ Magazine!

Also published in the October
AES issue of
Pro Sound News.

MORE INFO: Here's the unedited interview!

Mastered For iTunes - Apple Certified

Interview with Stephen Marcussen