I knew I should have re-read my post before hitting send...but I was late for leaving for the Cardinals v. Dodgers game (Cards won 3-2). Anyway, had I spent a more "editor" time, I would have said: Just as a comment...IN THE AUDIO WORLD balanced is... I'm actually an EE/CompE by degree and I have NO MEMORY of EVER studying this. Guess that explains that 2.74 GPA! :) Brian Brian Becker President, Poplar Bluff Internet, Inc. http://semo.net P.O. Box 190 | Poplar Bluff, MO 63902 | 573.686.9114 -----Original Message----- From: usr-tc-admin@mailman.xmission.com [mailto:usr-tc-admin@mailman.xmission.com] On Behalf Of Dave Martin Sent: Thursday, July 04, 2002 11:45 AM To: usr-tc@mailman.xmission.com Subject: RE: [USR-TC] The Balanced vs. Unbalanced discussion/definition...

AHHHH!! So which one is it??

There has to be an EE on this list somewhere.

Guilty as charged. Balanced signalling transmits a signal over a pair of conductors (usually referred to as "+" and "-") with opposite polarity in order to eliminate "common mode" distortion from external electromagnetic sources. EMF is induced equally in each of the two conductors and is cancelled out (to the extent of the common-mode rejection offered) at the receiving end of cable. No shield is technically required (unshielded twisted-pair [UTP] ethernet cabling is one example), but is often used, especially on analog (e.g. audio) cabling.

Charles

-- Charles Sprickman spork@inch.com

On Thu, 4 Jul 2002, Brian Becker wrote:

...

Just as a comment...balanced is required to have a ground and a shield to be defined as balanced. Of course much of the audio gear can survive if the ground and shield are the same signal, but it is not part of the spec and all major recording studios will utilize separate and distinct paths for the ground and the shield to reduce the level of noise to its minimum.

I am "Artist Formerly known as Brian Becker" with Benson Music Group, Nashville, (Christian Rock) and spent many hours working with top studios in Nashville & Houston...they would laugh at the thought of combining ground and shield.

Brian Becker President, Poplar Bluff Internet, Inc. http://semo.net

Home of TotallyFabricated.com Software & Web Design http://TotalScrutinizer.com - Tech Support Just Got Easier!

POBox 190 - Poplar Bluff, MO 63902 - 573.686.9114

-----Original Message----- From: usr-tc-admin@mailman.xmission.com [mailto:usr-tc-admin@mailman.xmission.com] On Behalf Of Jeff Mcadams Sent: Wednesday, July 03, 2002 6:31 PM To: usr-tc@lists.xmission.com Subject: [USR-TC] The Balanced vs. Unbalanced discussion/definition...

OK...this is probably rather off-topic, but there were a couple of different people participating, and it might be of interest to some, so feel free to delete if you're not interested.

Talked (via email) to my uncle who works for Sweetwater Sound (http://www.sweetwater.com) and owns his own sound studio on the side, about the use of the term "balanced" in audio gear.

He said that the term wasn't precisely defined (gee, sounds like the data world!), but that in his opinion it didn't require a ground line to be considered a balanced signal. He basically said that virtual every cable type that you'll run across in audio work *does* have a ground line (sometimes, its also the shield), so its kinda a moot point, but that its not strictly required. Indeed, he pointed out that it can be a *bad* thing to have ubiquitously connected ground lines in audio work.

He pointed out that the local ground of one piece of equipment may not be the same as the local ground of another piece of equipment, so since they are both grounded through their AC line, connecting the ground line between the two pieces of equipment can result in a voltage and waveform across the ground line, which can result in a hum in the signal.

He mentioned that the way they avoid this problem in his studio (plug: DSL Studios, http://www.dslstudios.com...hosted by IgLou ;) was to have every connection between different pieces of equipment run through patch bays. Each piece of equipment has its own ground (through the AC line), and the patch bay itself (a passive piece of equipment) is also ground, but that the ground line in the cable is *not* connected to the ground of the patch bay. This ensures that there is no continuous ground connection between two different pieces of equipment and avoiding a ground loop.

FWIW, he pointed out the use of the balancing concept at http://www.equitech.com...specifically "balanced power", ie, rather than having a hot line at 120VAC and a ground, you have two hot lines at 60VAC, but in opposite phase. When the power supplies in the equipment run by this looks at the two lines, it still sees 120VAC, but the opposite polarity of the lines means that the "reactive currents" coming back out of the power supply end up cancelling each other out, resulting in a significant noise reduction. I found it interesting that there's a third field where balancing is used.

Anyway...this is probably way more than most of you wanted to know, but I found the mental excursion interesting, hopefully others have found the discussion enlightening as well.

Let me know if anyone has questions, if I can't answer them, I'll get better answers from my uncle...he's *quite* knowledgeable about audio production. :) -- Jeff McAdams Email: jeffm@iglou.com Head Network Administrator Voice: (502) 966-3848 IgLou Internet Services (800) 436-4456

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-- ------------------------------------------------------------------------ Dave Martin Netcetera, Inc. dpm@netcetera.com "May the Foo be with you" ------------------------------------------------------------------------ _______________________________________________ USR-TC mailing list USR-TC@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/usr-tc