Balanced: 180 ͦinverse of signal. How? Or rather where?

[Graham Bernard]

OK, back to skool for me.

I understand the maths of the 180 ͦ inverse of signal will wipe out the noise that may have accrued do to the length of cable - I get that. What I do not get is just where does this inverse of signal happen? Please put me out of my misery.

TIA

Grazie

[Tony McGuire]

Graham,

Its all to do with the way balanced cable is made and the signal it carries. you have 2 wires that are twisted over the lenght of the cable. one carries a positive signal and the other carries a negative. The negative is a 180 inverse of the positive signal This is how one will cancel the noise it out.

this video may help

Balanced Audio vs. Unbalanced Audio Signals - Understanding how they work. - YouTube

[Graham Bernard]

Yes Tony, that's exactly the Video I've watched too and exactly why I'm here asking this question. I get the noise cancelling part, I really do, what I was wanting to know is just how, in all that's Faraday, that one of the signals gets inverted? How?

Grazie

[Tony McGuire]

It can be done as simple as using a passive DI box

http://www.expertsmind.com/CMSImages...ed%20loads.png


or

using op amp ics this would be like an actvie DI box

http://www.learningelectronics.net/c...it-diagram.jpg

hope this helps

[Graham Bernard]

Yes Tony, DI boxes, I have a Berhinger DI. I also understand about the transformers. But how does a Balanced cable make the Signal inverted? How?

G

[Tony McGuire]

Its not the cable that inverts the signal. It is the signal that is put into the balanced cable thats has the inverted signal. If you take DMX which also is a balanced signal of data. Even a network cable is a balanced cable which has 4 pairs for 4 separate data lines each one of them will have an inverted signal as well.

It will be the device that inverts one of the signals to help cut out the noise and interference

[Graham Bernard]

Originally Posted by Tony McGuire

It will be the device that inverts one of the signals to help cut out the noise and interference

Ah-ha! Got it, thanks. Obvious when I think about it. I was "mixing", no pun intended, the need to have BALANCED cabling from a guitar, to cancel noise and which doesn't generate a Balanced SIGNAL, with that, now I realise from you, of a device that WOULD send a balanced (inverted phase). My mistake.

So, balanced cabling is for already balanced outputs. Are you saying that the DI box will convert an unbalanced signal - say from a guitar - to a balanced (out of phase signal) ready for a balanced cable? I'm just using the guitar as a sample!

Tony, thanks for your patience,

Graham

[Tony McGuire]

No problem at all Graham.

I may have asked the same questions as yourself when I got in to sound and lighting a few years ago and thats a good few years. I am just getting in to videoing and I like it but there will come at some point to ask the odd questions that will have been asked 1001 times. We all have to start somewhere.

[Graham Bernard]

Ah, video! Bring it on!

[Steven Digges]

I think the input socket is worth mentioning here. Yes, the devices send and receive the balanced signal via balanced cable, but only if proper signal flow is maintained. Good questions Graham.

I think part of the confusion is because we are always talking about cables and pins, tips and sleeves as though they are the magic. They are simply the conductor for a signal. Remember that every time we talk about pins or tips/sleeves on a cable it means that those plugs MUST be connected to a compatible (similarly configured) input/output on both devices. In other words, using a 1/4 TRS Phono Cable (balanced) on any unbalanced in/out will not make the signal balanced. To complicate things further we can see rings and tips but we can not see the configuration of connectors inside a 1/4" input hole....and they are not all the same, far from it. That is why many devices have those little diagrams on the back of them that tell you what the contact configuration is. A TRS male jack will not always get the result you want in an unbalanced socket even if you are not expecting it to be balanced. There are other labels on some devices to help you understand connections. For example some 1/4 inputs on Mackie mixers are labeled BAL/UNBAL. That is telling you it is OK to use a Tip/ Ring cable for TR signal flow or it will send a balanced signal with a Tip/Ring/Sleeve cable. Input configurations are also available in the manual for almost every device made.

I am far from being a really knowledgeable audio guy. But I do have years of hands on experience and a solid foundation for much of it. What I know for sure is that the basics can take you far. Signal flow is everything. Always know where/how your sending it and what your doing to it on the way. That is the life blood of everything audio.

Kind Regards,

Steve

[Graham Bernard]

Steve, yes. Thanks for the in depth feedback.

OK Tomorrow I'm going to take pics of a range of rascals I've got plugged to my Behringer cable tester, and y'all can marvel at my range!

Anyhoo.... what I'm really about is to once and for all discover just which of my cables are Balanced and Unbalanced. I bet you can't wait? 😉

[Graham Bernard]

Tarah!

See the Cable Tester showing off its diagonal LED read out.

30 metre. Balanced XLR<>XLR:

http://www.dvinfo.net/forum/attachme...1&d=1504199465

2 metre Balanced XLR<>1/4 Jack

http://www.dvinfo.net/forum/attachme...1&d=1504199465

Phono<>Phono Unbalanced - I'm guessing?http://www.dvinfo.net/forum/attachme...1&d=1504199465

[Steven Digges]

Graham,

Yes, your XLR cable and your XLR/14" are balanced cables. Even though I cant see it the 1/4" plugs are TRS if your tester is working properly. There is no such thing as a balanced RCA cable.

Steve

[Richard Crowley]

In common, modern usage, if a connector has only two metallic contacts, then it is unbalanced by definition. You can easily see upon casual observation that an RCA connector, or a 1/4-inch TS connector can only be unbalanced. The outside shell of the RCA, or the sleeve of a 1/4 inch plug is ground/shield/signal return path, and the inside RCA pin (or the tip of the 1/4 inch plug) is the unbalanced signal path.

You need THREE contacts to make a balanced, shielded connection. i.e. a 1/4 inch TRS or an XLR. Pin 1 of the XLR, or the sleeve of a 1/4 inch plug are the ground/shield, while pins 2 and 3 of the XLR, or the Tip and Ring of the TRS are the balanced pair of wires for the signal.

While it takes a 3-pin plug/cable to properly transfer a balanced audio signal, the cable (and connectors) play NO PART in creating or receiving a balanced signal. It is the role of the source gear to CREATE the balanced signal. And it is the role of the destination gear to properly RECEIVE the balanced signal.

NOTE that just because a connector has 3 terminals does NOT imply that it is a balanced connection. The most common example of this situation is the headphone plug (whether 1/4 inch or 3.5mm) It has three connections for the earphones, but it is unbalanced, with the ground/shield/return path shared by the Left channel and the Right channel which are both UN-balanced.

[Graham Bernard]

Thank you very much gentlemen. You've locked in what I was crawling towards, it's good having one's peer group confirming and illuminating the dark corners. Thank you.