I am going to give you as complete an answer as I can as I am a huge fan of Balanced ( XLR ) connections from one piece of audio equipment to another.
But although the real answer is simple ( it is just a better way to get a signal from one piece of equipment to another ) most people like you are seeking a much more complex answer. Please forgive me if a couple of my facts are not 100% correct. I am going to do this from memory without looking up any of the facts.
I think it is best to begin with why RCA connections and Single Ended Cables are not the best way to go.
Originally the signal from one source component to another was run on a simple twisted pair of wire. This is a good solution as the outgoing and the return signal path is rather symmetrical but had one huge flaw ( especially when used with high voltage tube amplifiers ), it was subject to HUM. So eventually it was found that most of the HUM could be eliminated by SHIELDING the WIRES with a ground shield. Over time the twisted pair inside the ground shield ( now again very popular and known as the SHOTGUN TECHNIQUE ) got replaced by a single inner wire as that was most manufactures thought was all that was needed to make the connection. One outgoing thin center wire and a return GROUNDED SHIELD WIRE, and this is true. However this wire set up, although it works well is asymmetrical. The inner wire is thin and has a relatively high impedance and the outer shield is broad and usually has a lower impedance. Also ALL WIRE has a certain electrical characteristic and can be always modeled by an LRC circuit. Because the connection is an asymmetrical one, and because each wire is different ( different LRC Model values ) each wire can potentially sound different. Thus you have claims ( some of which are true ) that my wire sounds better than yours. Exotic wires sound better ( possibly ). Or no wire is perfect ( likely ). And your choice of wire may influence the overall sound of your system ( probably true as well ).
The RESURGENCE of an inner twisted pair inside the outer ground shield ( with the outer ground shield only connected at the source end - SHOTGUN directional wires ) gets us a little closer to a more perfect symmetrical connection and goes a long way to reduce wire differences and starts to get us back to some of the advantages of the true symmetrical balanced set up, but is still not as good as a true BALANCED CONNECTION using XLR connectors.
I hope I have gone into enough detail to explain why RCA single ended cables came about and how they evolved into first very inferior products, and how they are now beginning to de-evolve into better ( abet still imperfect ) interconnects.
Now onto Balanced connections:
To start with many TRANSDUCERS like a phono cartridge ( and GUITAR pickups ) for example are BALANCED DEVICES. That is that under natural circumstances both sides of the transducer FLOATS and NEITHER SIDE is CONNECTED TO GROUND.
Grounding one side, by random, makes for easier interconnections but spoils the BALANCED SYMMETRICAL NATURE of the device.
You are taking a perfect BALANCED DEVICE and forcing it to operate in unbalanced single ended mode.
Talking about strictly BALANCED DEVICES they have many advantages over single ended unbalanced devices.
First they produce equal output on both the POSITIVE and NEGATIVE leads. Thus if one runs BALANCED CABLES from a BALANCED DEVICE one has less distortion as all the COMMON MODES are taken into account.
For instance COMMON MODE REJECTION RATIO is improved.
Any distortion products that are COMMON to both sides are balanced out.
What comes out the end of a BALANCED WIRE is just the difference between the signal at the ENDS of the wires.
Nothing else matters.
What the wire is made of no longer matters as long as the wire is made properly in a symmetrical manner.
I also believe Signal Loss is LESS and SIGNAL AMPLITUDE is higher ( some of this is a little less clear to me than I would like ) and thus overall Signal to Noise Ratio is also IMPROVED.
Finally since the only thing that comes out as signal is the difference between the two wires at the end of a balanced connection as long as the cable is made as symmetrical as possible what the cable is made of no longer matters.
Thus I regress, no matter what the cable is made of, even if it made of cheap non oxygen free wire, as long as both the POSITIVE wire and the NEGATIVE wire are made of the same substance and as long as the wire is designed in a completely symmetrical manner, the sound will be exactly the same as a cable made of more exotic wire, as all the common modes cancel each other out, leaving only the differences in electricity at the ends of the output of the cable as the only thing that matters. So what goes in one end ( the beginning ) is the exact same as what comes out the other end ( the output end ). Thus I would like to expose that all well designed BALANCED CABLES sound the same as long as they are made properly.
Some people have also pointed out the balanced XLR connectors are symmetrical ( another advantage over asymmetrical RCA connectors ) and in general are better made and more secure connection than most RCA connectors, and this is also largely true.
So in summary ( in general all other things being equal ):
Balanced interconnects are always the way to go if you have the option.
Balanced interconnects need not be made of exotic wire or cable as long as they are made properly and are of symmetrical design ( this can save you a lot of money ).
They give you higher fidelity, lower distortion and better signal to noise ratio, and also a more secure connection.
RCA ( single ended ) cables should only be used when there is no alternative
When you have to use RCA single ended cables they should be made using the proper shotgun design ( an inner twisted pair with an outer ground shield connected at only the source end ),
You also might find that different single ended cables sound different in your system and might have to try a few or even many different cables to find a set that complement your system perfectly ( and the only way to really do this is trial and error ) and if you change just one thing in your system ( even just the position of the speakers in your room ) you might have to adjust your choice of single ended cables accordingly.
Not so with Balanced Cables which theoretically if made properly will all sound the same.
Michael A. Marks, MD
But although the real answer is simple ( it is just a better way to get a signal from one piece of equipment to another ) most people like you are seeking a much more complex answer. Please forgive me if a couple of my facts are not 100% correct. I am going to do this from memory without looking up any of the facts.
I think it is best to begin with why RCA connections and Single Ended Cables are not the best way to go.
Originally the signal from one source component to another was run on a simple twisted pair of wire. This is a good solution as the outgoing and the return signal path is rather symmetrical but had one huge flaw ( especially when used with high voltage tube amplifiers ), it was subject to HUM. So eventually it was found that most of the HUM could be eliminated by SHIELDING the WIRES with a ground shield. Over time the twisted pair inside the ground shield ( now again very popular and known as the SHOTGUN TECHNIQUE ) got replaced by a single inner wire as that was most manufactures thought was all that was needed to make the connection. One outgoing thin center wire and a return GROUNDED SHIELD WIRE, and this is true. However this wire set up, although it works well is asymmetrical. The inner wire is thin and has a relatively high impedance and the outer shield is broad and usually has a lower impedance. Also ALL WIRE has a certain electrical characteristic and can be always modeled by an LRC circuit. Because the connection is an asymmetrical one, and because each wire is different ( different LRC Model values ) each wire can potentially sound different. Thus you have claims ( some of which are true ) that my wire sounds better than yours. Exotic wires sound better ( possibly ). Or no wire is perfect ( likely ). And your choice of wire may influence the overall sound of your system ( probably true as well ).
The RESURGENCE of an inner twisted pair inside the outer ground shield ( with the outer ground shield only connected at the source end - SHOTGUN directional wires ) gets us a little closer to a more perfect symmetrical connection and goes a long way to reduce wire differences and starts to get us back to some of the advantages of the true symmetrical balanced set up, but is still not as good as a true BALANCED CONNECTION using XLR connectors.
I hope I have gone into enough detail to explain why RCA single ended cables came about and how they evolved into first very inferior products, and how they are now beginning to de-evolve into better ( abet still imperfect ) interconnects.
Now onto Balanced connections:
To start with many TRANSDUCERS like a phono cartridge ( and GUITAR pickups ) for example are BALANCED DEVICES. That is that under natural circumstances both sides of the transducer FLOATS and NEITHER SIDE is CONNECTED TO GROUND.
Grounding one side, by random, makes for easier interconnections but spoils the BALANCED SYMMETRICAL NATURE of the device.
You are taking a perfect BALANCED DEVICE and forcing it to operate in unbalanced single ended mode.
Talking about strictly BALANCED DEVICES they have many advantages over single ended unbalanced devices.
First they produce equal output on both the POSITIVE and NEGATIVE leads. Thus if one runs BALANCED CABLES from a BALANCED DEVICE one has less distortion as all the COMMON MODES are taken into account.
For instance COMMON MODE REJECTION RATIO is improved.
Any distortion products that are COMMON to both sides are balanced out.
What comes out the end of a BALANCED WIRE is just the difference between the signal at the ENDS of the wires.
Nothing else matters.
What the wire is made of no longer matters as long as the wire is made properly in a symmetrical manner.
I also believe Signal Loss is LESS and SIGNAL AMPLITUDE is higher ( some of this is a little less clear to me than I would like ) and thus overall Signal to Noise Ratio is also IMPROVED.
Finally since the only thing that comes out as signal is the difference between the two wires at the end of a balanced connection as long as the cable is made as symmetrical as possible what the cable is made of no longer matters.
Thus I regress, no matter what the cable is made of, even if it made of cheap non oxygen free wire, as long as both the POSITIVE wire and the NEGATIVE wire are made of the same substance and as long as the wire is designed in a completely symmetrical manner, the sound will be exactly the same as a cable made of more exotic wire, as all the common modes cancel each other out, leaving only the differences in electricity at the ends of the output of the cable as the only thing that matters. So what goes in one end ( the beginning ) is the exact same as what comes out the other end ( the output end ). Thus I would like to expose that all well designed BALANCED CABLES sound the same as long as they are made properly.
Some people have also pointed out the balanced XLR connectors are symmetrical ( another advantage over asymmetrical RCA connectors ) and in general are better made and more secure connection than most RCA connectors, and this is also largely true.
So in summary ( in general all other things being equal ):
Balanced interconnects are always the way to go if you have the option.
Balanced interconnects need not be made of exotic wire or cable as long as they are made properly and are of symmetrical design ( this can save you a lot of money ).
They give you higher fidelity, lower distortion and better signal to noise ratio, and also a more secure connection.
RCA ( single ended ) cables should only be used when there is no alternative
When you have to use RCA single ended cables they should be made using the proper shotgun design ( an inner twisted pair with an outer ground shield connected at only the source end ),
You also might find that different single ended cables sound different in your system and might have to try a few or even many different cables to find a set that complement your system perfectly ( and the only way to really do this is trial and error ) and if you change just one thing in your system ( even just the position of the speakers in your room ) you might have to adjust your choice of single ended cables accordingly.
Not so with Balanced Cables which theoretically if made properly will all sound the same.
Michael A. Marks, MD
