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What is the difference between balanced and unbalanced
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CedarTREEz4
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#1
2nd January 2009
Old 2nd January 2009
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What is the difference between balanced and unbalanced

Hey guys. Sorry for the newb question, but I'm just starting to get an understanding of what all this stuff is. So anyway, the title pretty much says it all. What is the difference between balanced and unbalanced anyway? Does plugging a mic into a balanced ruin the mic, or does plugging it into unbalanced ruin it, or does it not matter. Anyway, thanks ahead of time
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2nd January 2009
Old 2nd January 2009
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Quote:
Originally Posted by CedarTREEz4 View Post
Hey guys. Sorry for the newb question, but I'm just starting to get an understanding of what all this stuff is. So anyway, the title pretty much says it all. What is the difference between balanced and unbalanced anyway? Does plugging a mic into a balanced ruin the mic, or does plugging it into unbalanced ruin it, or does it not matter. Anyway, thanks ahead of time
google is your friend.
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2nd January 2009
Old 2nd January 2009
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Hey Cedar, I'll try to explain..........

An unbalanced audio path has two conductors. One carries the audio signal and the other is the shield/ground. There is nothing at all wrong with an unbalanced signal but at times can be susceptible to picking up interference from radio frequencies or electro magnetic fields causing noise and buzz and picking up the occasional radio station! In fact, a lot of gear is unbalanced on the inside even though it has a balanced input and output. Including some high end consoles.

A balanced signal has three conductors. It relies on a sum and difference principal.
Sum and difference is the combining (summing) of two signals that are out of phase from each other. Whatever doesn't cancel out is what you're left with (difference)

When two identical signals of identical amplitude (volume) are combined and one is 180 degrees out of phase from the other you have complete cancellation of that audio. However, if one of those signals is a different amplitude, you don't get complete cancellation. And it's this principal that makes a balanced audio path work.

The output from a balanced piece of gear will have the audio signal on pin 2 (hot). That same signal will be present on pin 3 (cold) however that signal is at a lower amplitude than the signal on pin 2. The shield/ground will be on pin 1.

When the signal reaches a balanced input, the signal on pins 2 and 3 are combined with either pin 2 or pin 3 (usually pin 3) out of phase. If that cable happens to pick up interference along the way, it will be on all pins, in phase together and at the same amplitude. When it gets to the input, pins 2 and 3 are combined out of phase and any signal exhibiting the same amplitude (the noise) will cancel out completely. Since the audio is at different amplitudes, it doesn't cancel out and you're left with the difference: clean audio!

Hope this makes sense somehow.

As for the mics, most all are designed with a balanced output and should be plugged in to the balanced input of a microphone amplifier (pre-amp)
Plugging a mic into an unbalanced input won't ruin anything but mics generate a very low level signal that needs lots of gain to bring it up in level. Amplifying a signal that much benefits from the noise canceling of a balanced connection.


-Scotty
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2nd January 2009
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Scotty's technical explanation was solid. In practice, having balanced cords means you can run cable runs for longer distances (10ft is the commonly accepted threshold) with less chance of AC current causing hum or electrical noise being picked up. Here's a secondary resource if you need it.
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2nd January 2009
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Thanks a lot guys, I think I understand now
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2nd January 2009
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This is a subject I was confused about myself, I appreciate the great explanation, the "canceling out interference" point really makes sense the way you described it.
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2nd January 2009
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Nice work scotty-o

Great explanation amigo
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2nd January 2009
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23rd September 2010
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does a HI-z input lose some signal when given signal? i have noticed my apogee ensemble loosing a slight high end frequency when applying a stereo L/R HI-z signal from my yorkvile 1/4 inch balanced connector cables when playing audio samples from my keyboard
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23rd September 2010
Old 23rd September 2010
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Quote:
Originally Posted by scotty-o View Post
The output from a balanced piece of gear will have the audio signal on pin 2 (hot). That same signal will be present on pin 3 (cold) however that signal is at a lower amplitude than the signal on pin 2. The shield/ground will be on pin 1.

When the signal reaches a balanced input, the signal on pins 2 and 3 are combined with either pin 2 or pin 3 (usually pin 3) out of phase. If that cable happens to pick up interference along the way, it will be on all pins, in phase together and at the same amplitude. When it gets to the input, pins 2 and 3 are combined out of phase and any signal exhibiting the same amplitude (the noise) will cancel out completely. Since the audio is at different amplitudes, it doesn't cancel out and you're left with the difference: clean audio!
Hi, I just wanted to clear up a bit of inaccuracy here. Pin 2 and Pin 3 have the exact same amplitude only 180° out of phase. Along a balanced line noise will be picked up in the same phase by both conductors. When combined at the balanced input, Pin 3 is put back in to phase with Pin 2 which will double the amplitude of the original signal (because they are summed) and (theoretically) cancel out all noise because now the noise on Pin 3 is 180° out of phase.

By no means my best explanation ever but it will have to do...

@griploc_1981: couldn't find the Ensemble specs on Apogee's site quickly so this is just guess. Hi-Z inputs aren't balanced and this is why you might loose some signal going from a balanced output. Just use the balanced line inputs on the back.
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23rd September 2010
Old 23rd September 2010
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Quote:
Originally Posted by Fast_Fingers View Post
Scotty's technical explanation was solid.
Er... actually it was quite wide of the mark and repeats the usual misunderstandings about the balanced audio interface.

Let me try to explain the salient points...

The term 'balanced' in this context refers to the impedance of the signal wires with respect to ground. They have to be equal. That's the only thing that matters and the only thing that makes a balanced interface balanced.

Not the equal and opposite polarity signal concept -- and not all balanced interfaces use equal and opposte signals as I'll explain further in a moment.

Let's take a step back and look at how the unbalanced interface works.

To convey any signal voltage from one place to another we need two wires. In the unbalanced interface one wire carries the variable signal voltage and the second wire carries the reference voltage from which that varying signal voltage must be measured. This is normally zero volts -- audio ground.

For convenience, that audio ground reference wire is usually configured as an overall screen, because that brings the advantage of capturing radio frequency interference and grounding it where it can do no harm to the wanted audio signal.

However, if that interference manages to get through the screen, it generates a voltage relative to ground and appears on the signal wire in exactly the same form as the wanted signal. The interference and the wanted signal therefore combine to form a new composite signal and the interference can't be detected or extracted as a separate entity by the receiving amplifier stage. Once the interference gets in, you're stuck with it.

Moving forward again to the balanced interface, here we usually have three wires -- two for the signal, serving basically the exact same roles as for the unbalanced arrangement in so far as one (or both) carries the wanted signal voltage while the other (or both) acts as the voltage reference.

The third wire is entirely optional but if present is configured again as an overall screen. It takes no part in conveying the signal or any voltage reference. It is purely there to help protect against radio frequency interference, and in many cases is not used or required at all (patch bay cords being a common example where the screen is often omitted).

Now, should the unwanted interference break through the screen it will try to induce a voltage in both of the two signal wires, in the same way as it did in the unbalanced example. Here's the critical thing, though: if those two wires have exactly the same impedances to ground, the induced voltage will also be exactly the same on both wires. On the other hand, if they have different impedances to ground (ie, they have unbalanced impedances), the induced interference voltages will be different on the two signal wires -- and we are completely skuppered!

Whereas the signal receiving input stage in an unbalanced system simply detects the signal voltage (wanted signal plus interference) on the signal wire, as measured relative to the ground reference carried on the cable screen, the balanced input stage is much more cunning.

The balanced input stage is a 'differential' input, which means that it has two input ports and it is only interested in the voltage difference between those two ports. If both ports see exactly the same voltage there will be zero output. No difference, no output! However, if they carry different voltages the output will be the difference between them.

If you have +1V on one input and -1V on the other, you'll get a 2V output signal. Equally, if you have +2V on one input and 0V on the other, you'll still get a 2V output. But if you have +1V on both inputs, you'll get 0V at the output.

So... because we have a balanced interface in which the two signal wires have identical impedances to ground, any interference signal will produce the same voltage on each wire. This is called a 'common mode' signal and it will be completely ignored (rejected) by the differential input stage -- and hence any interference is removed from the wanted signal.

As I've mentioned, the wanted signal has to be conveyed in such a way that it produces a voltage difference between the two wires. One way -- the 'traditional way' is to send exactly the same signal voltage on each wire, but with opposite polarities. (Not usually at different amplitudes, as was suggested in Scotty's post -- although actually that would still work, just with a lower output signal). This 'equal and opposite' format is what you would normally see from an output balancing transformer, or from a dual active output stage.

Because each wire essentially acts as the reference voltage for the other, with this 'equal and opposite' signal format the differential input stage sees a signal which is twice the size of either signal individually -- and this gives rise to the often talked about 6dB level hike it produces when compared to connecting the balanced output to an unbalanced destination.

Alternatively, there is no reason at all why one wire shouldn't be held at zero volts (audio ground) while the other carries the entire signal voltage on its own, as I illustrated earlier.

The difference in voltage between the two wires in this case, as detected by the differential input stage, is still the wanted signal. And provided the 'cold' side exhibits the correct impedance to ground necessary to balance that of the driven 'hot' side, the interference rejecting capabilities of the system remain unaffected and identical to the conventional 'equal and opposite' arrangement.

This configuration is often refererd to as 'impedance balanced' to differentiate it from the 'equal and opposite format', and it is becoming increasingly popular with manufacturers for several reasons. Firstly, it can be configured so that the signal level remains the same whether the balanced output is connected to a balanced input or an unbalanced one.

Secondly, it exhibits 3dB less inherent noise than the dual active arrangement (because there is only one gain stage involved instead of two).

And thirdly it is cheaper to implement than the dual active arrangement (because it requires only half the components).

So to sum up, the advantage of the balanced interface is that the wanted signal can always be separated from the unwanted interference signal -- but the whole thing relies NOT on the fact that the two signal wires carry equal and opposite signal voltages (because they don't have to be formatted that way, as I have shown) BUT because the impedances to ground for each signal wire are identical or balanced.

The theory is based on the Wheatstone Bridge if you want to investigate further.

Finally, it's probably worth mentioning that the signal wires in a balanced cable are twisted so that electromagnetic induction from nearby magnetic fields (such as from mains cables or transformers) cancels out over a short length of cable. Starquad cables manage better EMI rejection because the twist is tighter and there are four cores wired in opposite pairs to imporve the cancellation effect. The cable screen has little effect on EM interference, while the signal wire twisting has little effect on RF interference. Both are needed and serve different roles.

To answer the original question, "Does plugging a mic into a balanced ruin the mic, or does plugging it into unbalanced ruin it, or does it not matter" The answer is, it doesn't matter. However, phantom powered mics can only be used with a balanced connection because that's the only way phantom power can work, and without phantom power the mic won't work at all. Plugging the mic into an unbalanced input won't harm the mic, but it won't work either.

Plugging a non-powered mic into an unbalanced input will simply unbalance the output of the mic. No harm done and the mic will work... maybe it won't sound as good as it could, but it will still work.

Hope that helps -- sorry for the verbose reply, but it is inherently a slightly more complicated story than most people know or understand.

Just remember that 'balanced' means balanced impedance, not 'equal and opposite' signals. The latter might not exist but the system still works to reject interference. If the impedances aren't balanced it simply won't reject interference.
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24th September 2010
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Thank you for clarification!

So, I often see a word "quasi-balanced" for the design you mentioned as a recent trend, as opposed to the traditional/common "fully-balanced" design. But they are both "balanced" in terms of impedance to the ground, and "quasi" is such a misleading use of term, I think. It sounds inferior to me, but actually superior.

Also in this context, I prefer to use polarity (as you did), instead of phase which implies phase shift in the time domain, because polarity-reversed "cold" wire signal is not generated by the phase shift.
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24th September 2010
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What's the difference?
Mathematically it is 1.
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24th September 2010
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Thank you Mr Robjohns!!!

I think a light might well have switched on somewhere.
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24th September 2010
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Quote:
Originally Posted by Rick Sutton View Post
What's the difference?
Mathematically it is 1.
i like that one i was gunna go with "the difference is the 'UN'"
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25th October 2010
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So, better using balanced cables?
is TRS a balanced cable?
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25th October 2010
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Quote:
Originally Posted by CAMGRec View Post

google is your friend.
Yep.

...But sadly, the best I ever found is no longer there.

Good thing I saved this when I did:

Balanced Line Technology.zip

(Its a zip file of an html fileset.)
.
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25th October 2010
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As PDF file for archive.
Attached Files
File Type: pdf Balanced Line Technology.pdf (392.9 KB, 1325 views)
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25th October 2010
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25th October 2010
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Quote:
Originally Posted by hugerr View Post

Let me try to explain the salient points...
Thanks for this excellent post. There are a few subjects about which I liked to think I knew it all and this was one of them, but you proved otherwise here. It may have been a simple matter of perspective on the subject, but it was nonetheless enlightening.

(What's kind of facepalm-worthy here is that a significant portion of my final EE thesis involved best practices for wiring and grounding in audio systems!)
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25th October 2010
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Quote:
Originally Posted by sat159p1 View Post
So, better using balanced cables?
is TRS a balanced cable?
It depends on the situation! some call for balanced and some call for unbalanced

Yes, usually TRS and XLR are balanced. They use three conductor connectors, unlike unbalanced connectors/cables

Balanced VS Unbalanced Cables

Cj
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23rd September 2011
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So if a Balanced line is much cleaner (i.e. rejects RF) and can run long distances, then why is all equipment Not Balanced in the first place?
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23rd September 2011
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cost and other design considerations
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Quote:
Originally Posted by engineejoel View Post

So if a Balanced line is much cleaner (i.e. rejects RF) and can run long distances, then why is all equipment Not Balanced in the first place?
.
Short answer:
Because designing and building balanced circuits are a bit more expensive.
And also, it often doesn't really matter so much (as far as noise and interference specs go) with your typical short lines in the real world.
...Oh, and did I mention that unbalanced designs are less expensive?

.
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23rd September 2011
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Originally Posted by CAMGRec View Post
google is your friend.
Why not shut the forum down and let people find what they want to know by way of search engines? It would save bandwidth.
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23rd September 2011
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Another consideration (and it might have been mentioned in one of the voluminous posts) is that with unbalanced cables, they behave somewhat like a capacitor with respect to frequencies, and long runs of unbalanced cables can diminish high frequency response of mics and instruments. If AC hum from nearby power cords is ever an issue, use gaffing tape and place the two cords at 90 degrees to each other.
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23rd September 2011
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There is a term "common mode rejection" that if googled will explaine it as well.

Balanced equipment is (as mentioned) more expensive and requires either an input transformer or a differential amp at the front end. Unless this is very high quality it is just another stage of electronics to muck up your sound (of course induced EMR (hum) is worse :-). Some folks like the sound of a saturated transformer (myself included - if it's a good one) but that's another topic entirely :-).

If you're not having noise problems, balancing isn't necessary (but usualy doesn't hurt). Balanced lines will reject EMI electromagnetic interferance such as hum from power transformers or power lines (usually 60hz hum) but will not reject ESI electrostatic interferiance such as buzz from light dimmers, spark plug noise or arching neon lighting. This is a function of shield density (and a LOT harder to get rid of).
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23rd September 2011
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As already mentioned, lots of errors in the thread, some of them corrected by others.

One thing about impedance balanced interfaces though, you won't see 3dB less noise from this as compared to when both legs are active (carrying the signal) but actually 3dB more noise.

If we start with the unbalanced or impedance balanced signal and add a phase inverted equal signal via a separate active stage it means that the signal voltage will double (+6db) but the noise will only be +3dB. This means a better SNR with 3dB for the active balanced interface.

Another thing that separates the impedance balanced connection from the fully balanced is that the signal actually appears between pin 2 and ground which also means any cable capacitance affecting the signal will be the capacitance between one conductor and screen.

In the fully balanced interface the signal appears between the two conductors (or four in quad cables) and the capacitance between conductor and screen will stay out of the equation. The capacitance affecting the signal will be the one between the conductors.



/Peter
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23rd September 2011
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Quote:
Originally Posted by CAMGRec View Post
google is your friend.
Well, it's a couple of years later and I googled this question and this post was the top result. A bit more forward-thinking required with future smart-arse comments..?
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23rd September 2011
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Quote:
Originally Posted by Dogoth View Post
Balanced equipment is (as mentioned) more expensive and requires either an input transformer or a differential amp at the front end. Unless this is very high quality it is just another stage of electronics to muck up your sound (of course induced EMR (hum) is worse :-). Some folks like the sound of a saturated transformer (myself included - if it's a good one) but that's another topic entirely :-).
It's not expensive as all it take is one resistor at pin 3 at the sender and that the input of the opamp in the receiver is connected for a balanced signal. Almost all audio electronics has an opamp (discrete or IC) with an inverting input at the input stage.

Quote:
If you're not having noise problems, balancing isn't necessary (but usualy doesn't hurt). Balanced lines will reject EMI electromagnetic interferance such as hum from power transformers or power lines (usually 60hz hum) but will not reject ESI electrostatic interferiance such as buzz from light dimmers, spark plug noise or arching neon lighting. This is a function of shield density (and a LOT harder to get rid of).
To the best of my knowledge:

Balanced lines reject both EMI and ESI as long as the radiating element is at an equal distance from both conductors in the balanced cable and if the differential receiving amp is symmetrical.

An ordinary metal shield is effective as a shield to ESI and high FR EMI while Mu-metal is necessary to protect against LF and static magnetic fields.

High quality microphone and line level transformers (Jensen, Lundahl) use Mu-metal.


/Peter
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