how is noise cancelled in a balanced signal?

  • Thread starter Thread starter travelin travis
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Most of the time it is an op-amp, unless it is transformer balanced. That is pretty self explanatory. There really isn't that much to it, if you had a hard time wrapping your head around the noise cancelling benefits of balanced cable, your in trouble. This is much harder to explain.

Reading the posts, I think the thing that was confusing you was that you didn't see the two reverses of the signal. Or you weren't realising that it only eliminates transmission noise. (the noise that gets picked up by the cable) Not just noise in general.
 
Farview said:
Most of the time it is an op-amp, unless it is transformer balanced. That is pretty self explanatory. There really isn't that much to it, if you had a hard time wrapping your head around the noise cancelling benefits of balanced cable, your in trouble. This is much harder to explain.

Reading the posts, I think the thing that was confusing you was that you didn't see the two reverses of the signal. Or you weren't realising that it only eliminates transmission noise. (the noise that gets picked up by the cable) Not just noise in general.
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yea, i did'nt see where the signal was being brought in phase and the noise was staying out of phase. i get it now. you're probably right, i probably don't really want to go into an explanation of how the circuitry works.

i think bennychio11's explanation cleared it up pretty good for me. i'm like that though, i just have to know the basics of how things work in order to use them. thanks everyone for your time.
 
This is an excellent thread, and also backs up the assertion that "there are no stupid questions."

Well done, Travis.
 
thank you madaudio. i just hate having something like this hanging in the air. i must have answers! thanks again everyone.
 
ok, damnit.........i do want to know how the balancing circuitry works. :D

it's gonna bother me not to know. so if anyone knows, please explain. are certain frequencies seperated from the signal in the balancing circuitry?
 
The main thing with a balanced cable is that the shielding/ground is carried on a seperate, third conductor leaving the two "signal" conductors isolated. An unbalanced cable is two-conductor only with one of those conductors carrying the ground as well.

G.
 
SouthSIDE Glen said:
The main thing with a balanced cable is that the shielding/ground is carried on a seperate, third conductor leaving the two "signal" conductors isolated. An unbalanced cable is two-conductor only with one of those conductors carrying the ground as well.

G.
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this i did know but i thought that a balanced cable is called a 2 conductor cable and unbalanced cable is called a single conductor cable.

do you have any idea how a balancing circuit distinguishes between noise and good signal?
 
TravisinFlorida said:
do you have any idea how a balancing circuit distinguishes between noise and good signal?
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It doesn't really "distinguish", there is no "intelligence" being applied in the circuitry. It's much simpler than that.

What happens is the the signal on the hot and cold leads are inversions of each other (they are 180 degrees out of phase, so to speak.) The noise on both leads is of identical phase, however since the noise is basically the same.

The "balancing circuitry" simply flips the phase on one of the leads before summing the signals together. This puts the two signals - which were in inverted phase to begin with - back in phase with each other (doubling the amplitude while it's at it when the two now-in-phase signals are summed.)

But since the noise was in phase on the cable, when one of the leads is inverted, the noise on that lead is then inverted as well, So when the leads are summed, the "regular" noise on the one lead is cancelled by the inverted noise on the other.

In short, the key is that the signal on the two leads is in inverted phase on the cable but the noise isn't, So when the circuitry flips the phase off one of the leads, the signlas are now in phase but the noise isn't. So the noise gets cancelled but the signal doesn't.

G.
 
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SouthSIDE Glen said:
It doesn't really "distinguish", there is no "intelligence" being applied in the circuitry. It's much simpler than that.

What happens is the the signal on the hot and cold leads are inversions of each other (they are 180 degrees out of phase, so to speak.) The noise on both leads is of identical phase, however since the noise is basically the same.

The "balancing circuitry" simply flips the phase on one of the leads before summing the signals together. This puts the two signals - which were in inverted phase to begin with - back in phase with each other (doubling the amplitude while it's at it when the two now-in-phase signals are summed.)

But since the noise was in phase on the cable, when one of the leads is inverted, the noise on that lead is then inverted as well, So when the leads are summed, the "regular" noise on the one lead is cancelled by the inverted noise on the other.

In short, the key is that the signal on the two leads is in inverted phase on the cable but the noise isn't, So when the circuitry flips the phase off one of the leads, the signlas are now in phase but the noise isn't. So the noise gets cancelled but the signal doesn't.

G.
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So, using Bennychico11's ingenious drawing technique :D :

.....noise is the same phase on each lead when entering the balancing circuit:

+)+)+)+)+)+)+)+)+)+)+)+)
-)-)-)-)-)-)-)-)-)-)-)-)-)-)

.....the balancing circuit simply flips the phase of one of the leads:

+)+)+)+)+)+)+)+)+)+)+)+)
+(+(+(+(+(+(+(+(+(+(+(+(

.....the noise on each lead is now 180 degrees out of phase, which cancel each other out......

Is this right? Now I'm wondering how the noise is the same phase on each lead even though the leads are out of phase, before entering the balancing circuit.......and how does the circuit flip the phase of a signal.

thanks Southside Glen
 
TravisinFlorida said:
So, using Bennychico11's ingenious drawing technique :D :

.....noise is the same phase on each lead when entering the balancing circuit:

+)+)+)+)+)+)+)+)+)+)+)+)
-)-)-)-)-)-)-)-)-)-)-)-)-)-)

.....the balancing circuit simply flips the phase of one of the leads:

+)+)+)+)+)+)+)+)+)+)+)+)
+(+(+(+(+(+(+(+(+(+(+(+(

.....the noise on each lead is now 180 degrees out of phase, which cancel each other out......

Is this right? Now I'm wondering how the noise is the same phase on each lead even though the leads are out of phase, before entering the balancing circuit.......

thanks Southside Glen
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Yep, that's exactly right.

The reason that the signal is out of phase is because the signal is purposely inverted on the cold lead. The noise that we're talking about here is noise that is introduced into the cable from the outside "during the transmission in the cable" (e.g. RFI, induction noise, etc.) Because this noise is for all intents and purposes hitting both the hot and cold leads equally, both leads are getting the same noise - and therefore the noise is in identical phase on the two leads.

G.
 
TravisinFlorida said:
Now I'm wondering how the noise is the same phase on each lead even though the leads are out of phase, before entering the balancing circuit.......and how does the circuit flip the phase of a signal.
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because the noise enters it proportionally. the noise doesn't enter the cable from the microphone end like our original signal does...it enters the actual CABLE itself somewhere inbetween microphone and mixer. and because the leads are so close together in the cable, it has to hit each lead together in the same point of it's frequencies cycle.

and the circuit flips the phase of the signal just like Farview helped confirm....with the use of an opamp.

--edit---
Glen beat me to it ;)
 
this has cleared up alot of my questions. now, i need to go read and find out how an op amp and transformer work.

thanks fella's.
 
TravisinFlorida said:
this has cleared up alot of my questions. now, i need to go read and find out how an op amp and transformer work.

thanks fella's.
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You better be careful, Travis, you pull on this thread too hard and you'll wind up unraveling electrical theory all the way down to quantum dynamics, and then you'll really be confused! :D

G.
 
SouthSIDE Glen said:
You better be careful, Travis, you pull on this thread too hard and you'll wind up unraveling electrical theory all the way down to quantum dynamics, and then you'll really be confused! :D

G.
Click to expand...

lol, i agree.
stick with the recording process, and let the electrical engineers worry about how the insides of gear work....we have a more fun job anyway ;)

How electronics work can 'cause you headaches with all the information. Opamps themselves have so many different ways they can be configured for different uses. But go for it if you want...tread slowly and read and re-read. At least you're curious for knowledge, that's a good thing :)

http://en.wikipedia.org/wiki/Opamp

Good luck
 
TravisinFlorida said:
I am not walters! :D

just a dumb ass!
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Oh sorry Travis - I see Walters everywhere now...You're not a DA you're just interested in DA (differential amps). :D
 
Ok, I now understand how a transformer works. I read a bit on op amp theory and..........i'll have to get back to that some other time. I think I'll be alright with knowing what I have learned today........for awhile anyay.

Btw, thanks for the warning. Recording has become my diversion from playing guitar and I can see how electronics could carry me even farther away.
 
The easiest explanation I can think of is some basic algebra and three assumptions:

1. Most noise is picked up along the cable run, not in the hardware on either end. Balanced lines don't do anything to eliminate noise that is introduced outside the line itself.

2. You can invert a signal without adding (much) noise.

3. Any noise introduced in the cable is going to be either a positive or negative value in both wires. The actual value is immaterial, so long as it is the same for both wires.

Anyway, the signal is sent down one wire normally. Signal and noise are both positive. So we have:

wire_a = signal + noise

The signal is sent down one wire inverted (-). The noise introduced by the cable run is the same as on the other line. In other words, it is not inverted (+). So we have:

wire_b = -signal + noise

At the other end, the signal from the second wire is re-inverted and summed. The effect is that the inverted signal is subtracted from the non-inverted signal.

So starting with:

wire_a = signal + noise
wire_b = -signal + noise = noise - signal

We get:

wire_a - wire_b = signal + noise - (-signal) - noise

Since subtracting a negative value is the same as adding, this can be simplified to:

wire_a - wire_b = signal + noise + signal - noise
wire_a - wire_b = 2 * signal

Thus, any noise picked up by the cable itself is subtracted from itself, while the signal itself ends up being added to itself (well, its inverse is subtracted from itself, which is the same thing).
 
A plus and A neg equals A nothing.

yeah thats how i see the math too. xcept my explanation would include the 3rd line.

(Positive)........... LineA is + Noise and + Signal
(Negative)............LineB is + Noise and - Signal
(Inverted Line B)....Line C is -Noise and +Signal

(A+B)+C= +Signal only

So adding A+B= +noise, as the Signals cancelled each other out.

Then add C, and now the + and - noise cancel each other out, leaving only
the + Signal.


I think this is also why you see Microphones hanging upside down in the studios and more often than not the monitors are laying on their sides......
i think it makes sense to me...
 
COOLCAT said:
yeah thats how i see the math too. xcept my explanation would include the 3rd line.

(Positive)........... LineA is + Noise and + Signal
(Negative)............LineB is + Noise and - Signal
(Inverted Line B)....Line C is -Noise and +Signal

(A+B)+C= +Signal only

So adding A+B= +noise, as the Signals cancelled each other out.

Then add C, and now the + and - noise cancel each other out, leaving only
the + Signal.
Click to expand...

where are you getting this third line? there are only two conductors carrying our signal.

as far as your math though.... summing A+B (when A=B) noise would actually equal 2*(Noise)...you'd have double the amount of noise. So adding it to your "inverted" line with the -noise on it would only get rid of part of it.
make sense?
The GOOD signal never cancels out...we wouldn't want that. Only the noise cancels.


I think this is also why you see Microphones hanging upside down in the studios and more often than not the monitors are laying on their sides......
i think it makes sense to me...
Click to expand...

well, microphones hanging upside down in studios has nothing to do with noise, generally. It's more of a space reason to get the microphone and microphone stand out of the way....or for Tube mics. Our noise enters the microphone cable, not the microphone. So it doesn't matter where the microphone is.
as far as monitors on their sides...it's can be for the same reason. To get them out of the way, but also some monitors' manuals tell you to put them horizontal...other recommend vertical. I think this mainly has to do more with stereo imaging.
 
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