Balanced audio?

I work in so many places and with so many people where the concept of balanced audio (and the problems associated with unbalanced audio) haven’t quite hit home. But what is the difference?  Well, despite what you might have heard, it’s really quite simple.

Balanced-Audio2

We ‘balance’ the signal.  Essentially, the signal in the cable is carried down two wires, instead of one.  Each one is affected differently by any interference and can be compared later to find where the interference is and eliminate it.  That’s the easy explanation and not entirely accurate…

Ok, now if you get that, we can explain it properly.  How can you compare two signals and eliminate any interference in a simple analogue circuit?  Firstly, take the signal and create an identical but opposite signal.  So that is ‘phase inverted’.  These two signals are carried down two separate wires, the hot and the cold and they share a common ground giving a balanced signal 3 pins instead of the 2 pins used by an unbalanced signal.  So far, simple.

 

 

Now we can imagine that every interference ‘spike’ is a separate problem and deal with them individually.  Interference will cause an alteration in the sin wave as you can see in the diagram on the left and that alteration will be identical on both the hot and the cold wires.

 

Now if we just reverse the polarity of one of those signals again, both signals will look the same except for the interference spike which will be exactly opposite on both pins.  Now if those signals are joined back together to create a single signal, the interference will be completed cancelled out.

 

There are a number of other things that help such as impedance matching and shielded cables and perhaps we’ll look at those next…