Balanced vs. Unbalanced Audio

There are a lot of questions, and often confusion, surrounding balanced and unbalanced audio – What is balanced audio? Is balanced better than unbalanced? Why should I use balanced? How will balanced audio affect my system? What differences in sound quality can I expect to hear when using balanced? If balanced is so good, why isn’t everyone using it? …and the list goes on.

What follows is some insight into balanced vs. unbalanced audio in an attempt to answer these questions, ease the confusion, and explain how it is applicable today – particularly as high definition music gains popularity.

Unbalanced Audio Basics

Unbalanced audio is what you will be most familiar with; you use it whenever you connect a DVD player through the RCA jacks on your TV, hook some speakers to your computer sound card, or plug headphones into your iPod.

An unbalanced audio cable requires two wires, one wire for the signal and another for ground. Unlike balanced cables, unbalanced cables use the ground wire for the signal return. In typical unbalanced cables, the ground wire is the cable shield.

Unbalanced RCA inputs and outputs

An example of RCA sockets used for unbalanced audio inputs and outputs on a DAC Preamplifier

Common connectors used for unbalanced audio include RCA (as indicated above) and 1/8” mini (commonly found on computer sound cards).

Unbalanced audio is more susceptible to noise, so cable length should kept be as short as possible and it is important to keep unbalanced cables away from power cords and supplies.

Balanced Audio Basics

A balanced audio cable requires three wires, two wires for the audio signal and another for the shield. The audio signals on the two signal wires are equal, but of opposite polarity; one wire carries the positive (hot) audio signal, while the other wire carries the inverted negative (cold) audio signal. The third wire is usually a braided shield that wraps the two signal wires and is typically connected to ground (more on this later).

Balanced XLR inputs and outputs

Notice the XLR connectors used for balanced audio inputs are different to those used for outputs

The common connector used for balanced audio is the 3-pin XLR connector (as indicated above). 1/4” TRS phone connectors are also used although, while often used in professional audio, it’s rare to find them used for balanced audio on hi-fi components these days.

Balanced audio has higher noise rejection so is less susceptible to noise, allowing the use of long cables without degrading noise performance.

The Audio Interfaces in Operation

The Shield Conductor

In an unbalanced cable the shield is also the signal return, which can be troublesome on two fronts – interference picked-up by the shield will be inserted onto the audio signal, and any voltage difference between the grounds of the connected components will also appear on the audio signal.

The shield carries both the interference and the ground currents. Since the shield is the signal return, the voltage drop along the shield is combined with the signal the cable carries – resulting in noise and distortion being introduced directly into the audio signal.

In contrast, the separate shield conductor of a balanced cable does not carry signal, so the interference and ground currents in the shield do not introduce any noise into the audio signal – resulting in a clean signal, free of added noise and distortion.

There is one problem with the shield conductor in balanced audio, well it’s not an issue with the balanced audio interface as such, but rather how manufacturers terminate the shield in their equipment. It is what’s widely known as the “Pin 1 Problem” and has undeservedly tarnished the reputation of balanced audio.

Many manufacturers, consciously or unconsciously, connect the shield (pin 1 in XLR connectors) to signal ground. Currents induced into the shield that are allowed to flow in internal wiring, PCB traces or ground planes which are shared by the audio signal will degrade performance. The pin 1 problem can be avoided by paying careful attention to controlling signal and ground current paths or terminating the shield to the chassis.

Be aware that unbalanced audio inherently suffers from the pin 1 problem, since the shield conductor is the signal ground. The only way to address the problem in unbalanced audio is by strictly controlling signal and ground current paths.

Noise Immunity

The only line of defence against noise and interference for an unbalanced cable is the shield; even then it is only effective if the signal and ground current paths inside the equipment have been addressed. Shields do not block noise and interference entirely, they only reduce, or attenuate, it by a certain amount.

Once the noise has breached the shield there is nothing else unbalanced audio can do to attenuate the noise further. All that is left is filtering the signal at the receiver, which impacts sound quality by introducing additional phase shifts and losses. This is fine if the noise is outside the audio band, such as the high frequencies of RF – but what about 50/60Hz mains hum and its harmonics? Music wouldn’t sound so good if these frequencies were filtered out!

This is where balanced audio has it all over unbalanced and why professional audio has adopted balanced and used it from the outset. Balanced audio has a shield and two added lines of defence against noise and interference compared to unbalanced.

The shield of a balanced cable is more effective at blocking noise and interference than its unbalanced counterpart, provided the shield is correctly terminated to the equipment chassis. Still, it cannot block all of the noise and interference; this is where the “balanced” in balanced audio comes into play.

The two signal wires in a balanced cable make it inherently immune to noise and interference. Noise and interference is picked-up equally in both signal wires and, since the receiver is only interested in the difference between the positive and negative signals, the noise is cancelled out. This is called common mode rejection and the effectiveness of a balanced receiver to cancel the common mode noise is referred to as common mode rejection ratio (CMRR).

But that’s not the end of it, a balanced audio cable has a third mechanism for fighting interference – the two signal wires are typically twisted together to reduce interference from magnetic fields. A twisted pair makes the loop area between the signal wires as small as possible, and ensures a magnetic field that passes equally through adjacent loops induces equal levels of noise on both wires, which is cancelled out by the balanced receiver.

A Video Overview

I stumbled upon this video overview of balanced vs. unbalanced audio from Alectro Systems Inc., which does a good job of showing how balanced and unbalanced audio works and makes what I’ve discussed a little easier to visualise.

A few other excellent resources for the more technically inclined: Balanced Audio on Wikipedia, Henry Ott’s AES 2007 presentation Audio Interconnections and Grounding and a couple of tech notes from Rane Corporation – Grounding and Shielding Audio Devices and Sound System Interconnection

So What’s Wrong with Balanced Audio

Technically, nothing – balanced audio does everything you need in an audio interface and has far more potential than unbalanced audio. The only down-side to balanced audio is cost – as a consumer this means pricier cables with fewer cables to choose from, as a manufacturer it means expensive input and output circuits along with more costly connectors.

How well a balanced interface does its job basically comes down to two things – how well the signal lines are balanced and the CMRR of the receiver; both of which are expensive to implement properly and is why balanced audio typically only features on more expensive audio components.

It is quite conceivable to create a simple and inexpensive balanced output circuit from one dual op-amp package – but the cheap cost comes at the expense of performance, poor line balance due to mismatches in the source impedance severely degrades the noise rejection of the balanced interface. Therefore not all balanced audio interfaces are created equal; it requires expensive parts, such as audio transformers, precision op amps and discrete circuits to achieve the line balance and CMRR to realise the full potential of balanced audio.

As a designer I have justified the higher cost of balanced audio over unbalanced – it’s a small price to pay for the increased performance and the improvements in sound quality that balanced audio offers. I urge you to evaluate balanced audio yourself and see if you too can justify the higher cost.

How Will Balanced Audio Benefit You

It’s all good and well discussing the technical merits of balanced audio, but how is it applicable in the context of a home audio system, and what real-world improvements in sound quality can be expected.

The ability of balanced audio to reject noise and interference offers measurable improvements to signal to noise ratio and dynamic range – resulting in vivid, life-like performances presented against a quiet background, while revealing music’s subtle textures and intimate details.

Improvements to distortion are also observed as even-order harmonics generated by the balanced output circuit are typically cancelled by the balanced receiver – this gives a sound that is transparent and accurate, that resolves detail without grain or artefact.

Crosstalk is also reduced, not so much in the interconnect cables, since they are shielded, but certainly when using balanced audio inside the equipment – especially inside an amplifier where large currents result in high levels of emitted noise. Imaging becomes more precise with enhanced separation between instruments and an increased sense of air, while the soundstage sounds more three-dimensional – open and spacious with a greater sense of depth.

After extensive testing comparing our components in balanced and unbalanced modes, listening to music using balanced is always more convincing – producing performances which seem more compelling and credible with greater life and energy.

Balanced Audio in Today’s High Definition Landscape

High definition 24-bit music files have pushed the boundaries of resolution and dynamic range to new levels – no longer is 100dB dynamic range adequate to faithfully reproduce high definition music’s 144dB capabilities.

As high definition music becomes increasingly popular and more readily available, the improved dynamic range of balanced audio allows the full potential of high definition music to be harnessed.

So Is It All Worth It

When weighing up the pros and cons of balanced vs. unbalanced audio, balanced brings far more benefits to the table than it surrenders. For me, the higher cost of implementing balanced audio is a small price to pay for the improvements to sound quality that it offers.

Balanced audio offers true high definition performance to faithfully reproduce the high definition music that is available today and in the future – this is evident in the fully balanced Audiant DP32 preamplifier with on-board 32-bit/192kHz digital to analogue converter (DAC) and matching Audiant 100p power amplifier.

If you’re looking to get the most out of today’s high definition music, and can justify the higher cost of balanced interconnects, a balanced audio system is absolutely worth it.