Subject: RE: [USR-TC] The Balanced vs. Unbalanced discussion/definition...

From: Brian Becker <[email-masked]>
Date: Thu, 04 Jul 2002 15:27:45 +0000

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: [email-masked]
[mailto:[email-masked]] On Behalf Of Jeff Mcadams
Sent: Wednesday, July 03, 2002 6:31 PM
To: [email-masked]
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: [email-masked]
Head Network Administrator              Voice: (502) 966-3848
IgLou Internet Services                        (800) 436-4456

_______________________________________________
USR-TC mailing list
[email-masked]
http://mailman.xmission.com/cgi-bin/mailman/listinfo/usr-tc

---

From: Charles Sprickman <[email-masked]>
Date: Thu, 04 Jul 2002 16:18:27 +0000

AHHHH!!  So which one is it??

There has to be an EE on this list somewhere.

Charles

--
Charles Sprickman
[email-masked]

---

From: Dave Martin <[email-masked]>
Date: Thu, 04 Jul 2002 16:45:11 +0000

>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.

-- 
------------------------------------------------------------------------
Dave Martin                 Netcetera, Inc.            [email-masked]
                       "May the Foo be with you"
------------------------------------------------------------------------

---

From: Antonio Querubin <[email-masked]>
Date: Thu, 04 Jul 2002 19:27:34 +0000

> paths for the ground and the shield to reduce the level of noise to its

In the more abstract case "balanced" refers to forcing or guaranteeing the
return current follows the same path as the forward current, but just in
reverse.

- one could use a coax line and still be electrically balanced (as long as
the devices at each end do not share a common electrical return)

- one could have a paired line with a shield and still be unbalanced (if
one leg of the line is tied to a common electrical point)

It's not so much the type of physical cable in use that determines whether
a line is balanced but how that cable is used electrically and whether
there is a common electrical point (usually ground) between devices that
might possibly allow some return electrical current through a different
cable or path than the forward current.  Whenever that happens, the
likelihood of noise being picked up through electrical induction is
significantly increased.  I'll leave the physics explanation out... :)

---

From: Jeff Mcadams <[email-masked]>
Date: Fri, 05 Jul 2002 02:49:44 +0000

Also sprach Brian Becker
>paths for the ground and the shield to reduce the level of noise to its

I'm still skeptical that ground and shield are required for a signal to
be considered balanced, although I don't doubt that they are used pretty
much without fail in analog audio work.  I believe, however, that I
misstated what my uncle said earlier (having gone back and re-read his
messages to me).  I think his point was that there are seperate ground
and shield lines, but he said that the shield is at ground potential...I
made the (erroneous) mental jump of thinking that ground and shield were
the same line.

>combining ground and shield.

Man...all these years, the name "Brian Becker" was tickling the back of
my mind somewhere...but the lack of context prevented me from ever
making the connection.
-- 
Jeff McAdams                            Email: [email-masked]
Head Network Administrator              Voice: (502) 966-3848
IgLou Internet Services                        (800) 436-4456

---

From: Steve Monkhouse <[email-masked]>
Date: Fri, 05 Jul 2002 03:05:09 +0000

Im looking at having a play with some older edgeservers.. (the older
486 based models).. 

Ive got the edgeserver NAC, but no nic for it... can anyone tell me
about them, or point me 
in the direction of some edgeserver reference areas ??

What do they normally come with ? are they normally pre-loaded with
anything ?
are there any usr flash upgrades or anything i need to know about ?

regards

Steve

---

From: Lewis Bergman <[email-masked]>
Date: Fri, 05 Jul 2002 12:50:16 +0000

> paths for the ground and the shield to reduce the level of noise to its
I know when I used to deal in a ton of analog phone circuits they were 
commonly referred to as balanced. Of course these were common UTP phone 
cables without ground. We merely "balanced" them by adjusting the outbound 
voltage levels with the inbound voltage levels. This helped eliminate some 
signal to noise problems as well as assuring that the audio out was "as loud" 
as the audio in.

Maybe the confusion comes from crossing disciplines. Each industry has its own 
terms, some of which conflict with other fields.
-- 
Lewis Bergman
Texas Communications
4309 Maple St.
Abilene, TX 79602-8044
915-695-6962 ext 115