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Old July 11th, 2012, 07:09 AM   #1
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Someone please explain audio to me

Hi. I have a Sony PMW-EX1R. It has two unbalanced XLR inputs, and records two audio tracks. These two audio tracks, when examined with Premiere, QuickTime or any other relevant product, are both monaural.

Yet, an XLR input carries left and right channels separately. That's what the L and R stand for. The microphone that I usually connect to the XLR inputs is a stereo mic. And the EX1R has a camera-mounted stereo mic, which can be selected as the audio input for either or both of the audio channels. But the recorded audio is mono.

What am I missing here? What do I do to get a genuine stereo signal on one or both of these audio channels?

Richard
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Old July 11th, 2012, 07:46 AM   #2
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Re: Someone please explain audio to me

Quote:
Yet, an XLR input carries left and right channels separately. That's what the L and R stand for.
This is not correct for a typical 3-pin XLR. The L stands for latch and the R modifier means something
I don't understand historically. A 3 pin cable only carries one audio channel with balanced/push-pull
signaling. There may be a few audio technica single point stereo mikes that put unbalanced stereo
audio on the two pins rather than balanced audio but this is not standard usage. The EX1s are setup
for the normal professional usage which means one channel to one 3pin xlr.
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Old July 11th, 2012, 08:36 AM   #3
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Re: Someone please explain audio to me

Okay, thanks.

So monaural is all I can expect, I suppose. So does this mean that if I want to record a true stereo signal I need to use a separate audio set up?

Now why does the EX1R have a stereo onboard mic?

Richard
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Old July 11th, 2012, 08:41 AM   #4
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Re: Someone please explain audio to me

Concur with Dustin - 3 pin XLR is mono, balanced. Some people have used XLR cabling to route unbalanced stereo, but that's 100% not normal. I've never seen a camera or audio mixer input wired for stereo. I have some stereo balanced mics - and these use 5 pin XLRs up to the power supply/splitter and have two 3 pin outlets. The 'R' merely indicated rubber insulation on the sockets.
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Old July 11th, 2012, 08:55 AM   #5
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Re: Someone please explain audio to me

If your stereo mic has an 1/8" output then you have to get a splitter that splits the 1/8" TRS into 2 XLRs. Then in post pan your channels L & R instead of center.
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Old July 11th, 2012, 09:38 AM   #6
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Re: Someone please explain audio to me

The reason XLR has 2 audio signals is because the other is inverse. By design, the inverse signal is flipped when processed and that doubles amplitude and cancels out noise within the cable.
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Old July 12th, 2012, 03:57 AM   #7
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Re: Someone please explain audio to me

Thanks for all replies. I guess if I want a stereo signal, I have to do it in post. I'm not sure why the EX1R comes with a stereo mic, then, because it seems impossible to use it under any circumstances.

I'm aware of a stereo mic that produces a 5-pin XLR output. It can be split into two 3-pin XLRs. I guess if you want a true stereo signal, you have to use both of your audio channels to record the output of that. Or you can record your audio entirely separately.

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Old July 12th, 2012, 10:46 PM   #8
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Re: Someone please explain audio to me

Richard, I'm not sure what your problem is with the built-in stereo mic. Granted, using the camera mic is usually not a smart thing to do, but you can record stereo just fine with the EX1R. Just be sure you import your footage as stereo and not dual mono and you should be fine.
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Old July 12th, 2012, 11:36 PM   #9
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Re: Someone please explain audio to me

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Originally Posted by Richard Cavell View Post
Hi. I have a Sony PMW-EX1R. It has two unbalanced XLR inputs, and records two audio tracks.
No, it has two BALANCED audio inputs. Yes, it records to two audio tracks.

Quote:
These two audio tracks, when examined with Premiere, QuickTime or any other relevant product, are both monaural.
ALL audio tracks are "monaural". If you take them two at a time you can call one "Left" and the other "Right" which makes "Stereo".

Quote:
Yet, an XLR input carries left and right channels separately. That's what the L and R stand for.
No. All conventional XLR connections carry one channel only. "XLR" is the model number from back 50 years ago when Cannon added this style to its range of "X" style connectors. The "L" designated that they have a Latch, and the "R" designated that they had a "rubber" surround around the pins.
Ref: http://en.wikipedia.org/wiki/XLR_connector

Quote:
The microphone that I usually connect to the XLR inputs is a stereo mic.
Using a 3-pin XLR connector for stereo is a very unconventional method. Very few microphones (notably the Audio-Technica AT-822) used this arrangement.

Quote:
And the EX1R has a camera-mounted stereo mic, which can be selected as the audio input for either or both of the audio channels. But the recorded audio is mono.
You seem to be confused about "stereo" and "mono". "Stereo" is simply two mono tracks, one named "Left" and the other named "Right". Sometimes editing systems show them linked together as "stereo", but unless we are recording music or something, we typically split the channels apart so that we can deal with each separately.

Quote:
What am I missing here? What do I do to get a genuine stereo signal on one or both of these audio channels?
First, you are missing a correct understanding of "stereo" and "monaural". Second, you are missing a cable that takes your unbalanced stereo signal output from your microphone and splits into two conventional 3-pin XLR connectors, one for the "Left" channel and one for the "Right" channel. It appears that Audio-Technica doesn't make stereo microphones with that unconventional connector any more. (They use the modern standard of a 5-pin XLR connector). But you could make an appropriate adapter cable if you are handy with a soldering iron, or you could have one made for you by Redco (or other similar vendors).

If you want specific help (vs. generic discussions of XLR connectors) then you will need to reveal exactly what microphone you are working with.
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Old July 13th, 2012, 02:01 AM   #10
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Re: Someone please explain audio to me

Dave,

Sorry for being dense here. Let's say I take my EX1R and on the back panel select "INTMIC" for both audio switches. I don't connect anything to either XLR input. Now I record some footage, and import it. As I've said before, I use XDCAM Transfer because of the unique needs of the clients. Now I examine the resulting .mov file with Premiere Pro, or OS X Finder Info, and it clearly has 2 monaural tracks. If I examine the waveforms, they're identical. So how does this constitute a stereo signal? Why does the EX1R have a stereo mic and how do I record a stereo signal from it?

Richard
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Old July 13th, 2012, 07:18 AM   #11
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Re: Someone please explain audio to me

During the conversion to MOV's process, it by nature creates dual mono tracks instead of a single stereo track.

It is a simple task in Final Cut and Premiere to lay both mono tracks down on Tracks 1 and 2 and panning them Left and Right to achieve stereo. It should be a stereo signal if your pan pots are set correctly in the editing software.

I know in Premiere you can directly read folders with BPAV folders as XDCAM EX clips through it's internal Media Browser, so go to the folders you would normally use XDCAM Browser to work with and try opening up clips in the Media Browser to see if you can read it as a single stereo channel.

The only way I could see the signals being the same is if "EXT CH Select" in the "Audio Input" menu is a setting other than "CH1/CH2."
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Old July 13th, 2012, 08:20 AM   #12
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Re: Someone please explain audio to me

>The only way I could see the signals being the same is if "EXT CH Select" in the "Audio Input" menu is a >setting other than "CH1/CH2."

Aha! Thank you, Jack. That's the missing piece of my jigsaw puzzle.

If I otherwise want a stereo external mic, I use a splitter to record both channels on both of my EX1R's channels. And if I want anything more complex than that, I record audio separately. Case closed.

Richard
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Old July 13th, 2012, 09:12 AM   #13
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Re: Someone please explain audio to me

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Originally Posted by Richard Cavell View Post
Now I examine the resulting .mov file with Premiere Pro, or OS X Finder Info, and it clearly has 2 monaural tracks.
ALL audio tracks are "monaural". Sometimes we take them two at a time and call it "stereo". How the tracks appear in the file or in a video NLE application depends on other factors, but it doesn't change the fundamental content. XDCAM format actually provides four channels of recording, but most equipment only provides easy access to the first two channels.

Quote:
If I examine the waveforms, they're identical.
What does "examine" mean? Especially for co-incident pair stereo (like the microphones built into the camera), the waveforms look the same in the timeline. But if you LISTEN to them, you will hear the difference.

Quote:
So how does this constitute a stereo signal?
It depends on how you are defining "stereo". Technologically speaking, "stereo" means two independent channels of audio. Clearly the camera records two completely independent channels of audio. If you choose to call them "Left" and "Right" then it clearly records "Stereo".

OTOH, whether those two channels define a good representation of the original depends A LOT on the microphone(s) and where they are placed. You have not revealed WHAT you are recording, but the microphones built into a camera (ANY camera) are almost NEVER a good way to record something. And an external single-point stereo mic (as the one you mention, also not identified) may not be sufficient, either. When you get into microphone selection and placement, that is a whole new area of art and science.

Note that there is a separate forum here (and in most video websites) devoted exclusively to sound/audio. Microphone selection, positioning, and mixing is an endless topic of discussion. If you would like expert advice on how to record some specific kind of thing, the experienced audio people in that forum would be happy to offer their expert advice.

Quote:
Why does the EX1R have a stereo mic
All consumer and pro-sumer cameras have built-in stereo microphones. The mics built into camcorders typically cost only a few $ (typically <$10) and they wouldn't be able to sell their cameras without the microphones. Unfortunately, that causes people to think that a built-in microphone (or a microphone mounted on top if the camera) is an appropriate way to record something. When the fact is that a camera-located microphone is almost never a proper way to record something and is NEVER the best way.

Quote:
and how do I record a stereo signal from it?
If you have the controls set properly, you are already recording stereo from the built-in microphone.. If you don't like the sound of that, then you are validating the theory that a camera-located microphone isn't appropriate for your (undisclosed) application.
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Old July 13th, 2012, 11:03 AM   #14
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Re: Someone please explain audio to me

Richard,

You may already know this but just in case, your Rode NTG-1 will not give you a stereo recording if you split the signal going into the two channels of the EX1r. It will simply give you two channels of the same audio. If your levels are set the same, all you will have are two channels of the same recording. When played back out of two speakers it will still be a mono recoding. In order for you to get stereo from external mics you will need to either use two mono mics or a stereo mic with appropriate cables to connect each mic (or mic channel for the stereo mic) into the camera.

Like I said, you may already know that, I just didn't want you to go and get a splitter and think you'd get a stereo recording from your NTG-1.
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Old July 13th, 2012, 04:41 PM   #15
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Re: Someone please explain audio to me

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Originally Posted by Garrett Low View Post
You may already know this but just in case, your Rode NTG-1 will not give you a stereo recording
Wow, I kept thinking that the OP was talking about some OTHER (unidentified) stereo microphone. It never crossed my mind that he could believe that his NTG-1 is "stereo" by any stretch of the imagination. As you say, the only way to get "stereo" from an NTG-1 is to have two of them.
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