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Old March 17th, 2002, 01:48 AM   #1
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Balanced Audio vs Unbalanced Audio

Could someone please explain the benefits of balanced audio? If I was listening to balanced audio could I hear the difference over unbalanced audio? Is the difference similar to the difference between component video (HDTV of course) and RF on an old RCA super curved black and white tube TV? As I understand it (and I could be wrong) balanced audio basically ensures less signal degredation and interference. But is it truly the S-Video of audio?
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Old March 17th, 2002, 06:36 AM   #2
 
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Unbalanced audio, as you know, is a two conductor system of positive and negative microphone leads, with the negative lead sometimes forming a shielded lead around the positive. This setup, while offering some protection from spurious RF signal isn't completely adequate, since the shield lead can still pick up RF.

Enter the 3 conductor, balanced audio setup. In this case, the two microphone leads are shielded by a third lead. The third lead carries no power and is connected to system ground to dump any RF signal that is picked up.

A balanced audio line can be converted to unbalanced by connecting the two shielded leads of the balanced audio directly to a 1/8'" miniplug. There is no impedance matching when you do this, but, it works.

Hope this helps.
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Old March 17th, 2002, 10:29 AM   #3
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Sound-wise, there is little difference. On longer runs, however, balanced feeders are considerably less susceptible to hum induced by various power cables and wiring, with the lighting cables being the worst of the lot. While RF can be an issue, especially with every other person carrying a generator on his/her belt, ground hum is usually the biggest problem. Balanced feeders will tend to cancel much of this stuff out.

Going from balanced to unbalanced will have no little or no effect on the audio -- just keep it balanced until the last part of the run.
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Old March 17th, 2002, 12:59 PM   #4
 
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NEWS FLASH: Ground hum discovered by scientists to be RF.
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Old March 20th, 2002, 04:18 PM   #5
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"But is it truly the S-Video of audio?"

No. It does not separate any components of the signal.

What it does offer is, as explained by our friends Vic and Bill, superior grounding/shielding. Plus, since it is almost always low impedance, it is tolerant of a variety of devices that it gets fed to (a high impedance load can be driven by a low-impedance source but not vice versa), and is capable of supporting much longer cable lengths.

It is more than a coincidence that professional audio gear uses balanced (such as XLR) connectors, where consumer does not. Which gives us a kind of visual clue when looking at a piece of equipment that it is (usually) pro stuff if it has these kind of plugs.
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Old March 20th, 2002, 05:31 PM   #6
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Balanced allows for what is called common mode rejection. A signal that is the same in each wire is cancelled. The balanced lines run parallel (ususally as a twisted pair) and the theory is that any noise induced in one is also equally induced in the other wire. Thus the noise is cancelled.

Low impedance allows longer wire runs because at audio frequencies and for normal run lengths the capacitance of the cable is generally not significant compared to the system impedance, while it can be significant for hign impedance. High impedance mic lines are generally thought to peter-out at about 20 feet, a distance that might correspond to roughly 2000 feet for a low impedance line!

They also allow for fund things like phantom power and simplex communciation as well.
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Old March 21st, 2002, 02:20 PM   #7
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Hey, almost forgot about those "extras" so you can run those condenser mics and intercoms, something indigenous to studios.

Low impedance used to be an additional expense back in the days of tubes, due to the fact that the grid circuit of the input preamp tube was high-Z (typically 47K ohms) and required tran$former$ to match the signal coming in off the mic. And consumer gear was built to a price point, so such niceties were out of the question when it came to pinching pennies. But the advent of transistorized circuits threw that out the window.

Nowadays, it is so cheap to build lo-Z dynamic mics and preamp chips, the biggest upcharge associated with balanced lines is the higher price of XLR jacks and the cables. (versus RCA or Phone jacks and single conductor cable)
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Old May 2nd, 2002, 03:56 PM   #8
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"Going from balanced to unbalanced will have no little or no effect on the audio -- just keep it balanced until the last part of the run."

So does that mean that a Beachtek adaptor or the like is not really needed and I can just get the Radio Shack converter and won't hear much of a difference?
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Old May 2nd, 2002, 05:24 PM   #9
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Hmmm, what Radio Shack converter are we talking, madeline? And are you running a Canon XL1? If so, the Beachtek or Canon MA100 is a necessary accessory to pre-amplify the mic signal up to line level to feed the Audio 1 inputs, while turning balanced to unbalanced. If RS makes something equivalent to that (I don't know if they do or not), then you are in biz.

BTW, in the world of DJ audio, we mix unbalanced and unbalanced all the time. The pro mics are usually balanced with an XLR plug at the mic end, then the cable gets tied to an unbalanced 1/4 phone plug at the mixer end (which is what most DJ mixers have).
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Old May 2nd, 2002, 06:05 PM   #10
 
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Radio Shack makes a balanced to unbalanced converter. It includes an internal transformer for a better impedance match to unbalanced inputs, however, it has no amplification stage. Accordingly, just 'cuz you converted to unbalanced, you can't plug a mike output to a line level input....not enough signal. A pre-amp is needed. I use a Samson Mixpad4 that works great for this.
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Old May 2nd, 2002, 06:27 PM   #11
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Thanks for the recommendation/advice. I'm using a VX2000 which has a mic level input. I guess then the only remaining issue would be phantom power if the mic needed it.
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Old May 2nd, 2002, 06:58 PM   #12
 
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Several choices for phantom power. My Sennheiser ME66 has an onboard battery. Or, the Mixpad also provides phantom power.
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Old May 3rd, 2002, 07:03 AM   #13
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Question for the Machinist Mate

<< And are you running a Canon XL1? If so, the Beachtek or Canon MA100 is a necessary accessory to pre-amplify the mic signal up to line level to feed the Audio 1 inputs, while turning balanced to unbalanced >>

I'm a little confused. If the Audio 1 inputs are line level and the MA100/200 is converting mic->line, what does the Audio 1 In Menu selcection do to the signal?

When mic levels are input to MA100/200, should the Audio 1 In Mode be set to mic or line? I've been setting it to mic but your post seems to indicate it should be line.

Also, I'm pretty sure the Beachtek units *do not*amplify the signal. They can attenuate (mic/line switch) the signal but are otherwise passive devices.
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Old May 3rd, 2002, 08:20 AM   #14
 
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Even with the MA100/200 on my XLS1, the line/mic selection in the software menu has to be set to "line". Otherwise there is very little/no audio signal from the mike.
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Old May 3rd, 2002, 11:22 AM   #15
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OK maybe I am a little screwed up about this, but I do know that there is something along the lines of an op-amp or related circuitry inside the MA100 (some chips on a circuit board), and the submini plug is what I have been told is how this stuff in there gets powered. Maybe it doesn't boost the mics all the way up to line level, I have not tested this. But this is the only way I have fed my XL1 when using XLR-connected mics. When using a wireless receiver, I just unplug the on-board mic and plug it into that jack.
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