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Author Topic: Preamp polarity questions...  (Read 1360 times)

boogalaboogala

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Preamp polarity questions...
« on: September 09, 2005, 06:32:29 PM »

Hey all.

I have the following:

-ProTools 002R, running on an Apple PB G4
-R0DE NT1-A into a Presonus Eureka Preamp (Comp & EQ bypassed) with digital out
-MXL V69 ME with NOS Mullard tube into a Rane MS1b, into Eureka's 2nd digital out
-Both digital channels go into the 002 via high-quality S/PDIF

Now then, I am NOT looking for opinions on the gear, as valuable as yours may be.  I am wanting to know about the polarity switch on the Rane.

I just hooked up this signal chain to record acoustic guitar.  I love it.  The R0DE condenser is the main mic, placed at the neck/body joint, and it sounds bright and clear.  The MXL is the ambient mic, placed two feet back and directed toward the lower body of the guitar to pick up lower frequencies.  It sounds nice, too.

I played a song and recorded each mic to a mono track in PT.  Listening back, they each sounded great separately.  However, when I played them simultaneously, the Rane track sounded horribly strident.  So, I flipped the "Polarity" switch on the back from "Normal" to "Invert."  The difference was night-and-day better.  Panning the tracks left and right made it sound like I was playing a Jumbo on one mic and a Nashville on the other.  

My question is this:  What does this mean from here on out?  Is it normal to have to flip polarity (is phase the same thing?) on one mic when using two?  Does it have an effect on the recorded track that needs particular handling?  Does polarity even matter if the tracks are panned to opposite sides?  Is this a function of the difference in physical distance of each mic to the guitar (length of the sound waves)?

Any answers on this topic would be greatly appreciated.

Thanks!

Boog.


PS - Notice that I have disabled the Comp/EQ on the preamp.  I am trying to record as clean a signal as possible so that I retain production options later.  Keep this in mind when answering my questions.
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hargerst

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Re: Preamp polarity questions...
« Reply #1 on: September 10, 2005, 08:20:34 AM »

Whenever you point two mics at the same source, there is a possibility of phase cancellation.  Adjusting the distance of one mic will often help, and so can flipping the polarity switch.  It's usually best to fix it at the source by readjusting the mic distances, but if it works with the switch, use it.

Always listen to the track summed to mono to make sure you don't have phase problems.
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Harvey "Is that the right note?" Gerst
Indian Trail Recording Studio

boogalaboogala

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Re: Preamp polarity questions...
« Reply #2 on: September 10, 2005, 11:55:00 AM »

Brilliant!

Thank you, Harvey.

Boog.
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Luis Bacque

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Re: Preamp polarity questions...
« Reply #3 on: September 17, 2005, 01:00:38 AM »

Dear boogalaboogala,

my main preamps are

Avalon 2022 (Stereo)
Manley Dual pre (Stereo)
(coming neve 1073 dpd )

I never use the polarity button of my pres. I ALLWAYS find more results changing the distance of the mics to fix Phase Cancellation.

The instrument that I usually had problems of phase cancellation is my Steinway B. But the polarity buttons didn't solv it.

I bought a stereo pair of silver 414 and problems disapear. (when I got time to do a good micking)

The most popular setting to avoid phase cancellation is using a stereo pair of mics (matched pair from factory) X/Y position and use the same pres.

If you need to use different mics and different pres to get different colour to mix them later, I think that you ll get more results changing the distance of them. And of course like hargerst said, listen the two trks summed in mono and tell your assistant that start moving one of the mics at the recording room.

You can check it too with an analyser but in my case I prefer my ears.

I know there is people that resolve problems at the DAW, zooming and then moving one of the tracks, checking that the waveforms stay the most equal. Personnaly, I never had good results, maybe because I dont know how to do it right.


I hope this info be useful for you.

Regards.

Luis Bacque.





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Luis Bacque

Mandarina Sound Studios

Buenos Aires - Argentina
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