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What does it matter which XLR pin is hot on balanced gear?
Old 15th June 2005
  #1
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What does it matter which XLR pin is hot on balanced gear?

Everything I have is pin 2 hot, except my Otari MTR-12, which is pin 3,
but what does it matter?

because


Pin 2+ -------- Pin 2- ---------------- Pin 2+

Pin 3- ---------Pin 3+ ---------------- Pin 3 -




The same signal that goes into pin 2 comes out on pin two.
And the same for pin three.

What does it matter because pin 2 and 3 are duplicate signals of each other anyway?

I can see there being a problem if channel 1 of the Otari was pin 3 hot and channel two was pin 2 hot, but . . . . . . . . ?
Old 15th June 2005
  #2
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crypticglobe's Avatar
Quote:
Originally Posted by Jonk
Everything I have is pin 2 hot, except my Otari MTR-12, which is pin 3,
but what does it matter?

because


Pin 2+ -------- Pin 2- ---------------- Pin 2+

Pin 3- ---------Pin 3+ ---------------- Pin 3 -




The same signal that goes into pin 2 comes out on pin two.
And the same for pin three.

What does it matter because pin 2 and 3 are duplicate signals of each other anyway?

I can see there being a problem if channel 1 of the Otari was pin 3 hot and channel two was pin 2 hot, but . . . . . . . . ?


It doesn't matter at all. Phase is never an important part of recording...
Old 15th June 2005
  #3
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Okay,

So, by your tone, I'm guessing you're saying it really is going to matter?

I'm probably just going to open up those XLR's on the Otari and do a little flipparoo so I can feel better about it but I'd like to know why I'm doing that.
Old 15th June 2005
  #4
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sdevino's Avatar
 

As long as you know what is what and maintain consistancy it does not matter.

A problem would be if you sent signals from 2 different Mic pres to the Otari where one was pin2 hot and the other pin 3.

As long as you maintian the same reference for all your signals it should not matter.

Steve
Old 16th June 2005
  #5
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paterno's Avatar
 

Quote:
Originally Posted by sdevino
As long as you know what is what and maintain consistancy it does not matter.

A problem would be if you sent signals from 2 different Mic pres to the Otari where one was pin2 hot and the other pin 3.

As long as you maintian the same reference for all your signals it should not matter.

Steve
Technically, if your source wave is positive, you are printing an inverted signal to tape. It might not matter if you are not going anywhere with the tapes, but if you end up putting them up in an all pin 3 hi studio, [which actually do still exist] your polairty will be inverted. Plus, it might be an interesting experiment to see if you hear any difference if you polarity reverse the in and out of a particular channel so that the positive going wave hits the tape in the positive direction, and plays back positive relative to your pin 2 gear.

Some people can hear the difference in the polarity coming out of a set of speakers.

try it...

john
Old 16th June 2005
  #6
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max cooper's Avatar
 

IIRC, absolute polarity is considered most important when a waveform is assymetrical.
Old 16th June 2005
  #7
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brianroth's Avatar
 

For some time, Jay McKnight, head Guru ar MRL. has been trying to make up a database of the "internal polarities" of various makes and models of tape recorders. IOW, besides "which I/O XLR pin is hot, which is not", Jay believes there are inconsistencies once the signal trundles around through the internals of any given tape deck.

I believe there is an AES standard for this, but that doesn;t mean any given recorder follows that standard.

As for me, when in doubt, wire the XLR "properly", according to the standard the manufacturer chose. Tis been maybe 10+ years since I installed a new MTR-90 in a studio, but I wired the I/O with "red wire to pin 3" since that was Otari's chosen protocol.

Bri
Old 16th June 2005
  #8


Unless it's a religious thing, don't worry about absolute phase. Just make sure that the relative phase is consistent.



-tINY

Old 16th June 2005
  #9
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Fletcher's Avatar
It's not a "religious" thing, it's a science thing.

No amplifier, not even a "class A" amplifier work symmetrically [the top of the waveform is always different than the bottom], and the majority of the waveforms we record are asymmetrical [look at a vocal on an oscilloscope sometime]... so, ****'s going to sound different if you send it through a unit "upside down".

Now on an artistic level you might find you prefer the sound of sending something through an amplifier upside down... personally, I don't have the bandwidth for that level of minutia so I just try to keep things in my recording path the same polarity from start to finish... then if I want to flip the polarity for some kind of creative reason I at least know where I started.

BTW, the "polarity reverse" switch on most mic pre's comes after the input to the pre... in other words, you're reversing the polarity after it's gone through at least one amplifier upside down. The best way to change the polarity on the output of a microphone is with a polarity reverse cable.

Peace
Old 16th June 2005
  #10
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max cooper's Avatar
 

Right; some things are more symmetrical than others before they ever get to the mic, sine waves, for example, seem to be more symmetrical than things like voices and horns which seem to be the least.

I have one plug-in limiter that I use to chew up snare drums that has separate 'limit' controls for the 'push' and the 'pull' of the wave. Pretty handy once in a while.
Old 16th June 2005
  #11


Fletch -

You're right iff you are using a single-ended amp. If you use a push-pull amplifier topology the inversion will be perfect.

If you want to argue the linearity of the font-end diff pair, we can take it to GEEKdom, but I still say you're mistaken. At any rate, the polarity of speakers at the end of the line are going to matter a whole lot more (compressibility of the gas inside the cabinet gets involved).

Besides, there is no conclusive study showing that you can HEAR absolute phase.

But, I'll respect your temple....



-tINY

Old 16th June 2005
  #12
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I agree with tINY.

The input amplifier of a mic amp is 2 symetrical gain circuits, or a single class A where the output represents the difference between the inputs. If its a decent class A amplifier they should be linear on either side of the quiescent point.

I trust one's ability to detect absolute phase as much as I trust a wodden knob on a preamp to improve the sound stage. But assuming there are those that can..

As long as the polarity is consistant across the facility the recorded tracks will all have the proper relative polarity and the performance will have been preserved.

If the original poster records from pin 2 hot gear to a pin 3 hot recorder. Then if it is played back on pin 2 hot gear the original absolute phase will be maintained. If it is played back at the 1 remaining pin 3 hot studio then that studio is probably used to flipping the polarity for everthing that comes from outside anyway so it won't matter.
Old 16th June 2005
  #13
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Fletcher's Avatar
Quote:
Originally Posted by sdevino
I agree with tINY.

The input amplifier of a mic amp is 2 symetrical gain circuits, or a single class A where the output represents the difference between the inputs. If its a decent class A amplifier they should be linear on either side of the quiescent point.

The key word in that statement is "should". The fact of the matter is, they ain't.

There has never been a Neve module that amplifies the top of the wave identically to the bottom of the wave... the way you set the bias on a B283 card is to run a sine wave through the thing and try to get the top and bottom of the wave form as close to symmetrical as possible... I dare say that every other amplifier I've met, class A, class B, class A/B has the same anomaly.

I'm not talking about "absolute phase/positive polarity" [which I know people that can indeed hear it, and on some days I've been able to pick up on it, but the majority of the time the only way I know if I've attained "absolute phase/positive polarity" is with a piece of test gear].

My comments were purely about how a signal hits an amplifier... take it with whatever bag of salt you want... but I've heard it, I've measured it, so at least in my world, it's a "truth"... you can do whatever the phuck you want with your world.
Old 16th June 2005
  #14
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sdevino's Avatar
 

Quote:
Originally Posted by Fletcher
The key word in that statement is "should". The fact of the matter is, they ain't.

SNIP

My comments were purely about how a signal hits an amplifier... take it with whatever bag of salt you want... but I've heard it, I've measured it, so at least in my world, it's a "truth"... you can do whatever the phuck you want with your world.
And Every amp is going to have different upper and lower performance so its a pot shot and will never be reproduced unless played through exactly the same signal chain at the same temperature with the same humidity etc etc,

IMO this not one of the top 100 things to worry about in your recording other than be consistant.

Steve
Old 16th June 2005
  #15
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Fletcher's Avatar
I still think it usually sounds better to use a polarity reverse cable than the polarity reverse button on the desk 85 times out of 100... it's not that much of a time suck to install the cable rather than push a button [especially as we have an XLR to XLR patchbay in the control room that goes from the mic lines to the mic pre's].

I reckon YMMV but I don't know why it would.

Peace.
Old 17th June 2005
  #16
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by paterno
Technically, if your source wave is positive, you are printing an inverted signal to tape. It might not matter if you are not going anywhere with the tapes, but if you end up putting them up in an all pin 3 hi studio, [which actually do still exist] your polairty will be inverted. Plus, it might be an interesting experiment to see if you hear any difference if you polarity reverse the in and out of a particular channel so that the positive going wave hits the tape in the positive direction, and plays back positive relative to your pin 2 gear.

Some people can hear the difference in the polarity coming out of a set of speakers.

try it...

john
If you made pin 2 hot on both channels on one MTR-12 and played that back on a different MTR-12 with pin 3 hot it would be in phase, no problem. For a signal to cancel out because of being out of phase it has to be with respect the same source, for the most part..And as already stated as long as someone is aware of the pin out.
Old 17th June 2005
  #17
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brianroth's Avatar
 

Quote:
Originally Posted by nosebleedaudio
If you made pin 2 hot on both channels on one MTR-12 and played that back on a different MTR-12 with pin 3 hot it would be in phase, no problem. For a signal to cancel out because of being out of phase it has to be with respect the same source, for the most part..And as already stated as long as someone is aware of the pin out.
In the example you cite, the absolute phase of both channels would be reversed. Thus, instead of the kick drum "pushing" the monitor speaker outwards, the cone would be "sucking in".

Bri
Old 17th June 2005
  #18
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Fletcher's Avatar
Quote:
Originally Posted by brianroth
In the example you cite, the absolute phase of both channels would be reversed. Thus, instead of the kick drum "pushing" the monitor speaker outwards, the cone would be "sucking in".
In the cited example incorrect polarity was maintained into and out of the machine... the signal would go through the amplifiers and to tape upside down, but would go to the speakers right side up.
Old 17th June 2005
  #19
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brianroth's Avatar
 

I was referring to recording a signal into a machine that was delivered as "pin 3 hot", yet wired as "pin 2 Hot", then replaying the same piece of tape on another machine that was wired with correct absolute polarity.

Or am I missing something....

Bri
Old 17th June 2005
  #20
It won't matter unless you are converting a balanced signal to unbalanced. Or vice versa. Watch out for some otari recorders which use XLR outs but are wired unbalanced pin 3 hot. You will have phase reversal for sure there.

Jim Williams
Audio Upgrades
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