Views: 3554

Written by:

Balanced vs. Unbalanced: Prepared for Rejection


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!

6 Responses to :
Balanced vs. Unbalanced: Prepared for Rejection

  1. I’ve returned to this site several times because it’s given me a few tricks I would have never thought of myself. Thanks.

    I have a burning question that I’ve never been able to find a definitive answer for in all my years of audio engineering, and maybe you can shed some light, or at least wonder out loud with me– perhaps an “intermediate balanced” post in the future?

    I make my own audio cables because it’s cheaper and I’m not independently wealthy. My question is what to do with the ground on an 3 pin XLR cable? When dissecting factory manufactured XLR cables there doesn’t seem to be a standard method for terminating the ground wire: on some cables the ground is a “signal ground” and only connects to pin 1, and on other cables,the ground wire is jumped to the chassis (creating a “chassis ground”). Right now I’m just making cables with a signal ground running all the way through from pin 1 to pin 1 with no jump to the chassis.

    Reading the literature from Rode doesn’t help because they suggest everyone is doing it wrong and the only way to properly balance a 3 pin XLR cable is to completely disconnect the signal ground on one end of the cable (can’t remember which gender is unterminated off the top of my head). This practice doesn’t make the least bit of sense to me. AES literature is unforthcoming too and there seems to be a lot of infighting in the industry and no true standard yet. What gives?

  2. Dan Connor says:

    @ CHiTT Productions

    Thanks for the kind words! Funny you should mention that – one of my topics to write about in the future is ‘Making Your Own Cables’. For XLR cables, I’ve always done a ‘signal ground’ such as you describe, grounding to pin 1. While I worked at as an intercom technician at Telex Communications this is how we did it there, too. Rode’s assertion makes no sense to me, either. I can’t think of how that would be useful… unless maybe it was ‘signal gounded’ on one end and ‘chassis grounded’ on the other.

    Hope this helps. Thanks for reading!

  3. TeamScottSmith says:

    I’m sure Rode’s intent is to eliminate ground loops. Having a cable run from one bit of equipment with it’s power source, across a distance to another bit of equipment using a different power source,can create hum in the line. There can be a difference in potential between the two equipment grounds, that is equalizing itself through your cable’s ground wire.

    I wouldn’t build all my cables that way, I would deal with ground loops on a case by case basis. In a studio’s permanent wiring, I probably would drop the ground at the source end and tie it at the destination end, to avoid ground loops.

  4. Dan Connor says:

    That makes some sense.

  5. Andritch A. says:

    Cool…now what about usb connections? balanced? unbalanced?

  6. Dan Connor says:

    I guess it depends on the quality and type of the USB device. USB isn’t an analog connection – it’s not even a digital audio connection, strictly speaking. It also has bus powered voltage running through it…

Comments are closed.