unbalanced videomic pro going to give me bad audio?

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Brad Ballew

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unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 5:25 pm

So I recently purchased a rode videomic pro and a splitter that finally allowed me to get loud clear audio into my camera for nat sound. I really wanted something compact audio wise for b-roll shots. A buddy of mine tells me that I am losing half my signal going from an unbalanced mic to the BMCCs balanced input. He seems to think it will seriously hurt my audio. Am I in need of a converter or will my set up suffice for most b-roll situations? How bad is it going to hurt my audio?
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Rakesh Malik

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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 5:37 pm

My guess is that he doesn't know what balanced audio is. It sounds like he thinks it's stereo, which it isn't. It's a way of reducing how much noise a long cable run can capture, since it's very similar to an antenna, in that both antennas and cables are long conductors.

For short cable runs like the one from the mic attached to the camera to the camera itself, the advantage of balanced is pretty small compared to unbalanced, so the only real sacrifice you're making is in the preamp part of the chain.
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 5:55 pm

That's interesting you say that.

I've got a Rode Videomic Pro as well...but when I plug it into my BMCC, I get NO audio at all. The mic has a 1/8 stereo plug...that I'm attached to a 1/8 to 1.4 Stereo adapter...into channel 1 on the BMCC. Nothing.

Shouldn't this work?
Image

I have a few other mics, but they are XLR and I don't have an XLR to 1/4 TRS adapter yet, just mono...which of course, doesn't work.
Image

Did I mention I HATE audio?

sean
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Rakesh Malik

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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 6:15 pm

Most likely, it's not working because you made the same mistake as your friend. The output from the Video mic is stereo, not balanced. Balanced != stereo. I'm not sure about whether you NEED balanced inputs to get audio into the BMCC, because I've only tried it with balanced plugs. I got XLR to balanced cables from Sweetwater that connect from my MixPre-D to my BMCC (not really mine yet as I'm still waiting, but I tried this setup with a loaner from my vendor).

What you will probably need to get is a stereo to dual mono adapter and two 3/8" to 1/4" adapters. If you can find right angle adapters, it would be nicer for ergonomics, but I'm not sure where to find those. Possibly Laird?

The stereo output from the Videomic has two channels on one plug with a shared ground, while a balanced cable has one channel, a ground, and an inverted copy of the original channel. Of course, being a mono mic, the Videomic's output has two identical channels, unless you opted for one of the stereo models that Rode also offers. The mono version is most likely a lot more directed though, so it's probably a better choice for your application, once you get the right adapter.

If you have a good dealer around, take the mic + the camera in and tell them what you're trying to do. They'll most likely be able to help you get the right set of adapters.
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 7:21 pm

You need a cable like this:http://www.amazon.co.uk/3-5mm-Stereo-6-35mm-Audio-Cable/dp/B0034DSUMK/ref=sr_1_1?ie=UTF8&qid=1367435977&sr=8-1&keywords=3.5mm+to+balanced

Just using a 3.5 to 6.3 adaptor will not work.

I use that exact model of cable with a 3.5mm coupler (female to female) and my Rode VideoMic Pro and SVM work fine with the bmcc.
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 7:27 pm

I got this cable and it worked: http://www.radioshack.com/product/index ... Id=2103860

I also got a regular multimedia y cable that looked almost identical but didn't work at all. Someone who knows more about audio could explain why that is.

So am I not losing part of my signal using the aircraft y adapter and my videomic pro? It sounds fine to me, but my buddy told me that my audio could suffer under certain situations because I am not properly converting my unbalanced output to a balanced one...
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 7:53 pm

Tom wrote:You need a cable like this:http://www.amazon.co.uk/3-5mm-Stereo-6-35mm-Audio-Cable/dp/B0034DSUMK/ref=sr_1_1?ie=UTF8&qid=1367435977&sr=8-1&keywords=3.5mm+to+balanced

Just using a 3.5 to 6.3 adaptor will not work.

I use that exact model of cable with a 3.5mm coupler (female to female) and my Rode VideoMic Pro and SVM work fine with the bmcc.


So why doesn't my XLR to 1/4 plug work? (second photo) It's a single channel audio source into a single channel...although not balanced. I get no sound from this setup either...
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 7:58 pm

sean mclennan wrote:So why doesn't my XLR to 1/4 plug work? (second photo) It's a single channel audio source into a single channel...although not balanced. I get no sound from this setup either...


My guess is that it's due to not being a balanced connector. The XLR signal IS balanced, that's what XLRs are for. You may just need to change the XLR to 1/4 phono plug to one that's balanced. I'm using a pair of XLR to balanced 1/4 inch short cables (1 foot) and they worked fine on the loaner BMCC, as well as into a Zoom recorder.
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 8:04 pm

but the cable Tom posted above, from Amazon, splits a stereo 3.5 into 2 mono 6.3...and they are not balanced either and he says it works...so wtf?

See? This is stupid. LOL

Well, I'm going to pick up just such a splitter cable this evening and we'll see if that works. Also, I'll try to grab an XLR to 1/4 balanced cable as well.
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Re: unbalanced videomic pro going to give me bad audio?

PostWed May 01, 2013 8:19 pm

I've read conflicting reports of people having various levels of success with XLR to unbalanced 1/4" plugs.

The reason that I'm guessing that the balanced to unbalanced plug might be an issue is that balanced cables and connectors have two signal wires, one of which is inverted, while the unbalanced connectors have just one signal wire. The remaining wire is of course ground.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 7:04 am

The BMC connectors are balanced - just think of them as XLR in a different form factor.
So you need to have 3 cables and a jack with two black rings.

As far as I know, there are several ways to cable those plugs.

1. If you cable it wrong, the stereo channels cancel each other out and you hear nothing.
2. If you cable it wrong in an other way, you can hear something, but you loose 6db
3. The right way works.

There is also a different scheme if you come from a stereo source/mic or from a field mixer.
Also - as far as I know - the Rode VideoMic comes in different flavors, not sure if that helps, but maybe this is the reason why it works for some guys.
To add some confusion, my JuicedLink Riggy came with jacks that have only one ring, but it works fine.

All that cable stuff is way beyond me, maybe some audio guru can chime in.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 9:16 am

sean mclennan wrote:but the cable Tom posted above, from Amazon, splits a stereo 3.5 into 2 mono 6.3...and they are not balanced either and he says it works...so wtf?

See? This is stupid. LOL

Well, I'm going to pick up just such a splitter cable this evening and we'll see if that works. Also, I'll try to grab an XLR to 1/4 balanced cable as well.



The cable I posted is for going from the Rode Video Mic Pro or Rode SVM - not from an XLR based mic.

I cannot confirm whether it works from anything else, only that it works very well from those two mics directly into the bmcc.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 2:17 pm

I know Tom...I have a Rode Videomic Pro. I also have an XLR mic for VO stuff. I can't get either of them to work. Last night I bought a cable like the one you posted and I get no audio :\

Seriously, for all the details and steps BM goes through to ensure you use the right SSD, the only thing mentioned about audio is "balanced input".

To be clear, I have off camera recorder that I use for most of my production work. But I would still like to add better sound on camera (in a supplemental role) and I was hoping to use the Rode for that.

Still hate audio.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 2:51 pm

sean mclennan wrote:I know Tom...I have a Rode Videomic Pro. I also have an XLR mic for VO stuff. I can't get either of them to work. Last night I bought a cable like the one you posted and I get no audio :\

Seriously, for all the details and steps BM goes through to ensure you use the right SSD, the only thing mentioned about audio is "balanced input".

To be clear, I have off camera recorder that I use for most of my production work. But I would still like to add better sound on camera (in a supplemental role) and I was hoping to use the Rode for that.

Still hate audio.


If you have the same mic and same cable as I do, assuming your in camera settings are ok - then that sounds like you have a fault.

Could you show me the exact cable you bought?
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 4:02 pm

This video might help explain things better:

http://www.juicedlink.com/xlr-balanced- ... unbalanced

The camera can support both balanced and unbalanced signals without any issues (just like any other audio hardware can). You just need to make sure that if you're giving the camera an unbalanced signal via a TRS cable (i.e. one with two black bands), that the "tip" and the "ring" of the cable you're plugging in to the camera are NOT the same signal - otherwise they cancel each other out and you get no sound. A really simple fix would be simply cut the "ring" cable inside the adapter that plugs into the camera.

The advantage offered by TRS connectors used for balanced inputs is that a standard unbalanced signal lead using a TS jack can simply be plugged into such an input. The ring (right channel) contact then makes contact with the plug body, correctly grounding the inverting input.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 4:28 pm

Chris Hocking wrote:This video might help explain things better:

http://www.juicedlink.com/xlr-balanced- ... unbalanced

The camera can support both balanced and unbalanced signals without any issues (just like any other audio hardware can). You just need to make sure that if you're giving the camera an unbalanced signal via a TRS cable (i.e. one with two black bands), that the "tip" and the "ring" of the cable you're plugging in to the camera are NOT the same signal - otherwise they cancel each other out and you get no sound. A really simple fix would be simply cut the "ring" cable inside the adapter that plugs into the camera.

The advantage offered by TRS connectors used for balanced inputs is that a standard unbalanced signal lead using a TS jack can simply be plugged into such an input. The ring (right channel) contact then makes contact with the plug body, correctly grounding the inverting input.


Ok do you see the line going through the waves in the link? My buddy told me that going from an unbalanced output to a balanced input would eliminate the part of the wave below the line. That seemed odd to me. Is he misunderstanding how these signals work? Is the primary advantage of using balanced signals eliminating interference over longer distances? Does balanced vs unbalanced really matter when I am using a rode mic with a 6 in cable going directly in the camera?

Thanks for the link by the way.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 4:38 pm

Brad Ballew wrote: Is the primary advantage of using balanced signals eliminating interference over longer distances?


Correct. Many microphones operate at low voltage levels and some with high output impedance (hi-Z), which makes long microphone cables especially susceptible to electromagnetic interference. Microphone interconnections are therefore a perfect application for a balanced interconnection, which cancels out most of this induced outside noise.

Brad Ballew wrote:Does balanced vs unbalanced really matter when I am using a rode mic with a 6 in cable going directly in the camera?


No. The Rode Video Mic just has a unbalanced dual-mono 3.5mm mini-jack output. The microphone wiring itself is unbalanced, so there is no possible way to get a balanced signal from the mic to the camera without additional hardware.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 4:51 pm

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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 5:07 pm

So the input doesn't HAVE to be balanced then?
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 5:21 pm

sean mclennan wrote:So the input doesn't HAVE to be balanced then?


Using a regular ole y cable that just splits the signal won't work. However, the cable I got which is actually used for aviation does: http://www.radioshack.com/product/index ... Id=2103860

Someone who knows more about audio than I can explain why..


Brad Ballew wrote:
Does balanced vs unbalanced really matter when I am using a rode mic with a 6 in cable going directly in the camera?


Chris Hocking wrote:
No. The Rode Video Mic just has a unbalanced dual-mono 3.5mm mini-jack output. The microphone wiring itself is unbalanced, so there is no possible way to get a balanced signal from the mic to the camera without additional hardware.


Let me rephrase my question because I didn't convey what I was getting at very well. I have a cable, the one mentioned above, that brings the signal into the camera in a way that I can finally get a loud and clear sound in my camera. To me it sounds great. However, I am being told that if I don't take that signal through a converter that would convert it from unbalanced to balanced that I am going to run into problems because apparently I am losing part of my signal by bringing an unbalanced signal into a camera that really wants a balanced signal. So I guess my question is this: is there really a need to add a converter that would convert my signal from balanced to unbalanced if I am only going to have my mic on top of my camera with just a few inches of cable connecting the two? Obviously if I was connecting to a mic on a boom pole 20 feet away then balanced would be the way to go..
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 9:19 pm

Brad Ballew wrote:I have a cable, the one mentioned above, that brings the signal into the camera in a way that I can finally get a loud and clear sound in my camera. To me it sounds great. However, I am being told that if I don't take that signal through a converter that would convert it from unbalanced to balanced that I am going to run into problems because apparently I am losing part of my signal by bringing an unbalanced signal into a camera that really wants a balanced signal.


That's still false. The extra conductor on a balanced cable is carrying an inverted version of the same signal as the signal conductor. It's to reject noise in order to enable long cable runs. What you need is, and apparently have, is the correct adapter, not a converter. The only thing you're losing is the ability to run a 40-foot cable run, which you don't need so you're not missing out on anything.

If you want better sound quality for your film work, you'll have to get a field recorder. That said, the on-board sound recorder on the BMCC is sufficient for dialog.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 9:33 pm

sean mclennan wrote:So the input doesn't HAVE to be balanced then?


No - it does not. If your cable run is only very short, and you have a microphone mounted to the camera, the benefits of using a balanced cable would be minimal if not non-existent.

Brad Ballew wrote:So I guess my question is this: is there really a need to add a converter that would convert my signal from balanced to unbalanced if I am only going to have my mic on top of my camera with just a few inches of cable connecting the two?


In terms of balanced vs unbalanced - no, you do not need any additional hardware. In your case the microphone itself is unbalanced, so you will achieve no better quality "converting" it to balanced before sending the signal to the camera.

Again, the only benefit of balanced is noise removal as explained in the video I linked to. Technically, all that's happening is you're sending the same audio signal down two cables (instead of one), with one of those signals "inverted", and then simple maths is used to deduct any noise picked up along the cable run. There's no magic involved - you're basically just using maths to remove any noise floor introduced into the cable.

Putting the balanced vs unbalanced issue aside for a moment - I'd still STRONGLY recommend using an external pre-amp/mixer (such as a juicedLink BMC366 Low-Noise Preamp or Sound Devices MixPre-D). This will ensure your connection from the camera to the mixer is balanced, and give you much better pre-amps (as the internal pre-amps in the camera are pretty cheap and nasty).

However, going back to the balanced vs unbalanced discussion, here are some common situations (hint: when I say "JACK" I'm referring to a 1/4inch (6.35mm) phone plug - such as is found on the side of your Blackmagic Camera. When I say device, I mean microphone or other input):

- If you have an UNBALANCED MONO device then you need to use a MONO JACK (i.e. a one black band - tip and sleeve) to go into the camera.
- If you have an UNBALANCED STEREO device then you need to split the signal into TWO MONO JACKS (i.e. a one black band - tip and sleeve) and go into the two inputs in the camera.
- If you have a BALANCED MONO device (i.e. a microphone with an XLR), then you need to use a STEREO JACK (i.e. two black bands - tip, ring, sleeve) to go into the camera.
- If you have a BALANCED STEREO device then you need to split the signal into TWO STEREO JACKS (i.e. two black bands - tip, ring, sleeve) to go into the camera.
- If you have an UNBALANCED device that's only a very short distance away from the camera, then just connect it directly to the camera.
- If you have an UNBALANCED LINE LEVEL device (such as a Rode Video Mic) that's FAR AWAY from the camera (i.e. you have a Rode Video Mic on a boom pole), then the cheapest solution is to use a DI unit, DI box, direct box, or simply DI (variously claimed to stand for direct input, direct injection or direct interface) to connect your high-impedance, line level, unbalanced output signal to a low-impedance microphone level balanced input, usually via XLR connector.

Hope this helps!
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 9:34 pm

Tamerlin wrote:
Brad Ballew wrote:I have a cable, the one mentioned above, that brings the signal into the camera in a way that I can finally get a loud and clear sound in my camera. To me it sounds great. However, I am being told that if I don't take that signal through a converter that would convert it from unbalanced to balanced that I am going to run into problems because apparently I am losing part of my signal by bringing an unbalanced signal into a camera that really wants a balanced signal.


That's still false. The extra conductor on a balanced cable is carrying an inverted version of the same signal as the signal conductor. It's to reject noise in order to enable long cable runs. What you need is, and apparently have, is the correct adapter, not a converter. The only thing you're losing is the ability to run a 40-foot cable run, which you don't need so you're not missing out on anything.

If you want better sound quality for your film work, you'll have to get a field recorder. That said, the on-board sound recorder on the BMCC is sufficient for dialog.


Exactly. What Tamerlin said.
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Re: unbalanced videomic pro going to give me bad audio?

PostThu May 02, 2013 9:44 pm

Chris Hocking wrote:Exactly. What Tamerlin said.


You were probably still typing when I posted. :)
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Re: unbalanced videomic pro going to give me bad audio?

PostFri May 03, 2013 3:52 am

Thanks guys!! I have other audio equipment for when I do sit down interviews but I really needed something at least halfway decent for b-roll nat.

Thanks for clarifying the unbalanced vs balanced issue.
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Re: unbalanced videomic pro going to give me bad audio?

PostFri May 03, 2013 9:41 am

What Tamerlin said is exactly right. The whole 'balanced' signal technique, which uses three wires, is ingenious, and it provides a very low noise technique to send a weak signal from a microphone over many feet of cable in an electrically noisy environment (e.g. with power cables crossing it, maybe radiating digital cables, etc.) and really pull it off. It is THE WAY TO GO in cabling between a shotgun mic, for example, and your recorder / preamp/ camera, where you typically have a 25 ft cable for that, or maybe a 15 ft cable plus an internal coiled cable in a boom pole. So balanced audio is great stuff for us video shooters. However, a 2-ft shielded cable from a Riggy Micro to the BMCC input may not need to be balanced.

What BMD did, in this case, is correct (half way, anyway): they provide balanced inputs to support proper balanced cable to a typical shotgun mic. They use 1/4" instead of XLR to save space, but it is just as robust, and merely needs the right plug. 1/4" is industrial stuff used by musicians everywhere. What BMD did NOT do is provide phantom power, which is used on all of the pro-grade shotguns out there. That is a faux pas. So we have to provide something in between to fix that.

If a cable is made properly, you should be able to connect an unbalanced signal (e.g. from a Riggy Micro) to the BMD balanced inputs. Since two of the legs, as Tamerlin said, on a balanced cable carry inverted signals, relative to the ground, if you had the SAME signal on both, the input circuit would try to sum them the wrong way, and you would definitely get cancellation, which is bad news. Cutting one fixes it. If you put this on a scope, it would be obvious. Your cable must feed left channel to BMCC left input and right channel to right input. If it tries to feed a mono signal in 3-wire fashion (where you have one ground and left and right channels, but both are the same) to a single plug of the BMCC, you have made the mistake.
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Re: unbalanced videomic pro going to give me bad audio?

PostFri May 03, 2013 2:08 pm

sean mclennan wrote:I know Tom...I have a Rode Videomic Pro. I also have an XLR mic for VO stuff. I can't get either of them to work. Last night I bought a cable like the one you posted and I get no audio :\

Seriously, for all the details and steps BM goes through to ensure you use the right SSD, the only thing mentioned about audio is "balanced input".

To be clear, I have off camera recorder that I use for most of my production work. But I would still like to add better sound on camera (in a supplemental role) and I was hoping to use the Rode for that.

Still hate audio.



Maybe because your XLR mic needs phantom power?
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Re: unbalanced videomic pro going to give me bad audio?

PostFri May 03, 2013 2:58 pm

DNomer wrote:What BMD did, in this case, is correct (half way, anyway): they provide balanced inputs to support proper balanced cable to a typical shotgun mic. They use 1/4" instead of XLR to save space, but it is just as robust, and merely needs the right plug. 1/4" is industrial stuff used by musicians everywhere. What BMD did NOT do is provide phantom power, which is used on all of the pro-grade shotguns out there. That is a faux pas. So we have to provide something in between to fix that.



I think BMD based that decision on both the preference to maximize the life of the internal battery and the assumption that if you're recording to the camera, you're going to be using a preamp anyway, as will be the case in pretty much every professional setup. Using the preamp for phantom power makes sense, and it allows BMD to cheap out on the preamps on their camera, instead concentrating on what we care about cameras for, which is to be cameras.

If you're recording with dual system sound and using the camera sound for scratch, you'll still be using your preamp for phantom power.

:)
Rakesh Malik
Cinematographer, photographer, adventurer, martial artist
http://WinterLight.studio
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