This post focuses on the differences between balanced and unbalanced connections.
When I first started engineering my high school band, I didn’t know what the difference between balanced and unbalanced connections was. I used guitar cables to link up all of 1/4″ gear and routinely used impedance transformers to convert between XLR to 1/4″ unbalanced. I thought the extra ring on TRS cables was just some weird novelty. Not so.
When a signal flows through a cable it becomes subject to noise the longer it runs. This noise comes from stray electrons from the environment and takes the form of white noise. Unbalanced lines are basically two conductors and are susceptible to noise. Balanced connectors take care of this problem rather ingeniously. In a balanced cable, an extra conductor is added, twisted together. The audio signal is sent down both the added conductor and the original conductor, but 180 degrees out of phase (meaning that if the two signals were added together, you’d end up with nothing).
The theory is that, over the course of the run of the cable, both conductors will be exposed to more or less the same noise. As the two signals are complete opposites of each other, the only thing they will have in common will be the noise. Thus, if the audio system discards what the signals have in common and keeps what is different, you’ll end up with the signal without the noise. Ingenious!
Consumer vs. Pro Audio Signal
Another difference between unbalanced and balanced lines has less to do with the lines themselves and more to do with the standard ways in which they’re used. Consumer gear is almost always calibrated for -10db signal levels. Pro Audio gear that uses balanced lines generally has the default option of taking and providing +4db signal. There’s a 14db difference between the two. This is used in order to increase the signal-to-noise rating of pro audio signals (meaning the signal is 14db louder than the noise than it is in an unbalanced system). This means that if were were to interface a pro audio piece of gear into a consumer piece of gear without adjusting the pro audio gear, the consumer gear may be overdriven, producing distortion. Running consumer gear into pro audio gear without adjusting the pro audio gear to -10db will simply produce a low level.
Common Types of Balanced Connectors
Balanced connections generally use these kinds of connectors:
1/4″ TRS – a quarter-inch jack with a Tip conductor area, a Ring conductor area, and a Sleeve conductor area. Physically the same as ‘stereo’ jacks – but stereo isn’t balanced, it just adds another conductor for the extra channel.
XLR – the three-pinned microphone style connector. Yes, there are stereo XLR jacks – they usually have five or six pins (only five pins are technically needed because they can have a common ground).
TTL TRS – TTL stands for ‘tiny telephone line’. It’s basically somwhere between a 1/8″ mini jack and a 1/4″ in size. It’s mainly used in patchbays (originally used for… telephone patchbays).
Common Types of Unbalanced Connectors
RCA – the standard consumer audio plug (circular with a single, thick pin in the middle).
1/8″ mini TS – a consumer ‘headphone’ style plug but with just Tip and Sleeve (meaning mono).
1/8″ mini TRS – usually means stereo, not balanced… but technically could be used for a balanced signal.
1/4″ TS – a quarter-inch connector with just Tip and Sleeve. An instrument cable, for example.
Nowadays I use balanced connections more than I use unbalanced connections (the only time I use unbalanced connections are with instruments). I’ve learned: balanced rules!