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Old 9th April 2012, 08:34 PM   #1
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Default Balanced vs Unbalanced -Basics

Hi

I just had to explain some basics in an email, so I thought I would share them here as well.
I guess most of you on here are very familiar with these concepts, but for those who aren't, here they are:

Balanced Signals 101

Balanced signals are very clever and simple, and were developed to eliminate (or drastically reduce) interference coming onto the cable.
Any interference picked up by the cable of an unbalanced signal is added to the signal (as noise) and can never really be removed. -Problem!

Balanced signals have a duplicated version of the signal, but with reversed phase to the original signal.

So there are opposite (phase-reversed) versions of the signal on the two diferent wires, which are subjected to the same interference producing identical noise.
Signal: Positive phase + Negative phase
Noise: Positive phase + Positive phase
Then, the clever bit is what happens in the receiving equipment (input).
The extra (phase-reversed) signal gets phase-reversed back to the same as the original signal, and the two get added together.
Any Noise (interference) on the extra (balancing) wire/signal, gets phase-reversed, and added to identical noise on the original signal.
Signal: Positive phase + Positive phase = Double
Noise: Positive phase + Negative phase = Zero!
So any interference gets canceled out completely as long as it is identical on both wires.

Balanced signals basically have unbalanced signals in them already, they just have an extra signal as well (-to 'balance' the unbalanced signal).
As long as you keep any level differences (+4dB vs -10dB) in mind, going from Balanced to unbalanced is very easy because you can just forget about the extra bit, and only make use if the perfectly good unbalanced signal which is there already.

So going from Balanced output to Unbalanced input is literally as good as going Unbalanced all the way.

It would seem though that going from Unbalanced output to Balanced input should be more of a problem. But in fact, all that happens is you get a slight drop in signal level -which on most equipment makes little difference anyway due to good input vs output impedances.
All we need to do is connect the cold pin to ground on the balanced input (no need to do this on balanced outputs) to keep it at zero (same as ground).
Then when it is phase reversed and added to the original signal, it has no effect.


Balanced signals have much much better immunity to interference than Unbalanced signals do, and so the shield becomes less important -especially if the interference can be kept identical on the two wires. This is where twisted pair technology comes from.

Confusion can come from the many different standards of audio signals, cables and connectors.
For instance a balanced TRS (Tip, Ring, Sleeve) Jack would carry, 1 audio channel on 2 wires and a shield. -Hot, Cold, and Ground. Tip would be Hot and would use the Red wire. Ring would be Cold and would use the White or Black wire, and Sleeve would be Ground using the Shield.
But the same Jack and cable could be used (like for headphones) to carry 2 channels of unbalanced audio. -Left, Right, and Ground. Tip in this case would be left which importantly would be White or Black (Not Red like for a Balanced Signal), Ring would be Right and would use Red, and Sleeve would be Ground.

By accidentally connecting a balanced output via some off-the-shelf adaptor into a stereo input, you end up playing out-of-phase versions of only one channel out of the 2 speakers.

Consider a situation I have seen a few times where a stereo unbalanced signal gets plugged directly into a single balanced input. The Right channel gets phase-reversed, and added to the Left Channel. Anything that was the same in both channels (usually all the bass, and lead vocals in music) gets completely cancelled out, and what you are left with is the difference between the 2 channels (usually very thin-sounding background effects, reverb etc.) !

anyway..
-so now you know.
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Old 9th April 2012, 08:40 PM   #2
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Default see ridiculous diagrams

unbalanced signal.jpg

balanced signal.jpg
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Old 10th April 2012, 09:32 AM   #3
AndrewT is offline AndrewT  Scotland
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Post2 drawings are very informative, not ridiculous.
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Old 10th April 2012, 10:28 AM   #4
SY is offline SY  United States
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You might add the most important requirement- the impedance of each of the polarities to ground is equal.
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Old 10th April 2012, 04:57 PM   #5
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Quote:
Originally Posted by Raphael Shaw View Post
Hi

I just had to explain some basics in an email, so I thought I would share them here as well.
I guess most of you on here are very familiar with these concepts, but for those who aren't, here they are:

Balanced Signals 101

Balanced signals are very clever and simple, and were developed to eliminate (or drastically reduce) interference coming onto the cable.
Any interference picked up by the cable of an unbalanced signal is added to the signal (as noise) and can never really be removed. -Problem!

Balanced signals have a duplicated version of the signal, but with reversed phase to the original signal.

So there are opposite (phase-reversed) versions of the signal on the two diferent wires, which are subjected to the same interference producing identical noise.
Signal: Positive phase + Negative phase
Noise: Positive phase + Positive phase
Then, the clever bit is what happens in the receiving equipment (input).
The extra (phase-reversed) signal gets phase-reversed back to the same as the original signal, and the two get added together.
Any Noise (interference) on the extra (balancing) wire/signal, gets phase-reversed, and added to identical noise on the original signal.
Signal: Positive phase + Positive phase = Double
Noise: Positive phase + Negative phase = Zero!
So any interference gets canceled out completely as long as it is identical on both wires.

Balanced signals basically have unbalanced signals in them already, they just have an extra signal as well (-to 'balance' the unbalanced signal).
As long as you keep any level differences (+4dB vs -10dB) in mind, going from Balanced to unbalanced is very easy because you can just forget about the extra bit, and only make use if the perfectly good unbalanced signal which is there already.

So going from Balanced output to Unbalanced input is literally as good as going Unbalanced all the way.

It would seem though that going from Unbalanced output to Balanced input should be more of a problem. But in fact, all that happens is you get a slight drop in signal level -which on most equipment makes little difference anyway due to good input vs output impedances.
All we need to do is connect the cold pin to ground on the balanced input (no need to do this on balanced outputs) to keep it at zero (same as ground).
Then when it is phase reversed and added to the original signal, it has no effect.


Balanced signals have much much better immunity to interference than Unbalanced signals do, and so the shield becomes less important -especially if the interference can be kept identical on the two wires. This is where twisted pair technology comes from.

Confusion can come from the many different standards of audio signals, cables and connectors.
For instance a balanced TRS (Tip, Ring, Sleeve) Jack would carry, 1 audio channel on 2 wires and a shield. -Hot, Cold, and Ground. Tip would be Hot and would use the Red wire. Ring would be Cold and would use the White or Black wire, and Sleeve would be Ground using the Shield.
But the same Jack and cable could be used (like for headphones) to carry 2 channels of unbalanced audio. -Left, Right, and Ground. Tip in this case would be left which importantly would be White or Black (Not Red like for a Balanced Signal), Ring would be Right and would use Red, and Sleeve would be Ground.

By accidentally connecting a balanced output via some off-the-shelf adaptor into a stereo input, you end up playing out-of-phase versions of only one channel out of the 2 speakers.

Consider a situation I have seen a few times where a stereo unbalanced signal gets plugged directly into a single balanced input. The Right channel gets phase-reversed, and added to the Left Channel. Anything that was the same in both channels (usually all the bass, and lead vocals in music) gets completely cancelled out, and what you are left with is the difference between the 2 channels (usually very thin-sounding background effects, reverb etc.) !

anyway..
-so now you know.
There's some misinformation here:
The + and - signals only need to have the same impedance.
There is quite a bit of difference between signal earth and chassis earth.
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Old 10th April 2012, 05:35 PM   #6
AndrewT is offline AndrewT  Scotland
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Then show the alleged "errors" and delete from the quote all the content that is not controversial.
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Old 11th April 2012, 04:48 AM   #7
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Quote:
Originally Posted by AndrewT View Post
Then show the alleged "errors" and delete from the quote all the content that is not controversial.
The purpose of a balanced connection is to isolate the audio signal from its surroundings so nothing can alter it. This is accomplished by:
-Putting the audio signal into a Faraday cage.
-Twisting of the audio cables to cancel out magnetic interference.
-Using a separate circuit path for the audio signal and a separate circuit path for the electrical interference signals. The signal path for the audio is the + and - cable. The signal path for the electrical interference is the shield of the cable and the earth itself. The signal path for the interference signals is also the Faraday cage.
The AES48 standard of interconnects explains it all. aes48-2005-f

If signal earth and the shield of the cable are directly connected (witch is the case in 99% of all situations) then every electrical interference signal will go directly into the audio signal. Not a "High End" situation imo.
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Old 11th April 2012, 04:59 AM   #8
MiiB is offline MiiB  Denmark
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In most high end cables shield is only terminated in the TX-end..where the node is low impedance.. That's why good cables are directional,
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Old 11th April 2012, 08:55 AM   #9
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Originally Posted by MiiB View Post
In most high end cables shield is only terminated in the TX-end..where the node is low impedance.. That's why good cables are directional,
That is because there are 3 situations:
1 unbalanced where the shield is connected to signal earth.
2 balanced where the shield is connected to the chassis earth. (AES48)
3 balanced where the shield is connected to the signal earth. (Normal but wrong situation) Of cause all electrical interference goes directly into the audio path and its no better than using unbalanced connections.

You can not directly connect a balanced connection to an unbalanced connection because of ground loop hum. To prevent hum you need a D.irect I.njection box. These are expensive, people don't have enough knowledge, its a recipe for rip-offs.
So the money concious equipment manufacturers came up with a very cheap solution: Situation 3 I just described. Now you can connect unbalanced to "balanced" and no hum. This is the cause of the "pin 1" problem because when the shields (witch is the path of the electrical interference) are now connected the power supply ripple is injected into the audio signal.
More info here: Sound System Interconnection

So either use unbalanced or use AES48 everything else is a rip off.
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