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If you've spent any time around audio gear, you've undoubtedly heard terms like "balanced" and "unbalanced" connections, often associated with cables like XLR or ¼-inch TS/TRS plugs. But what do these terms actually mean? Why do we have both types, and how exactly do they work? Let's dive in and find out.
Rule of Thumb: Use balanced connections for long cable runs and interconnecting line-level equipment (mixers, interfaces, powered speakers) to ensure clean audio.
One common source of frustration in audio is unwanted noise – that persistent hum, buzz, or static noise. Often, the cables connecting your gear can be the culprit. They can act like antennas, picking up stray electromagnetic interference (EMI) and radio frequency interference (RFI) from the surrounding environment. The longer the cable run, the more susceptible it is to picking up this interference. It's worth noting that this type of noise pickup along the cable length is distinct from hum specifically caused by ground loops, another common audio problem related to the grounding between different pieces of equipment – you can learn all about diagnosing and fixing ground loops in our dedicated article here.
When the audio connection carrying your signal is unbalanced, any noise induced onto the cable gets mixed right in with your audio. The receiving equipment can't distinguish the unwanted noise from the actual signal it's supposed to amplify. Thankfully, there's a powerful technique designed specifically to combat this noise: balanced audio connections.
To understand balanced audio, we first need to grasp the concept of audio phase and cancellation. Imagine you have a simple audio signal, like a sine wave. If you duplicate this signal onto a second track in your DAW, both signals are perfectly "in phase" – their peaks and valleys line up exactly. Playing them together just makes the sound louder.
Now, what happens if you take that second track and invert its polarity (often called "flipping the phase") by 180 degrees? Its peaks now align perfectly with the original signal's valleys, and vice versa. When you play these two signals together, they completely cancel each other out, resulting in silence! This principle of cancellation using polarity inversion is the secret weapon used by balanced audio connections to eliminate noise.
An unbalanced connection uses a cable with only two conductors: one carries the audio signal, and the other serves as the ground reference (which is often also connected to the cable's shield). A standard guitar cable with TS (Tip-Sleeve) ¼-inch plugs is a perfect example. The Tip carries the signal, and the Sleeve is the ground. Any noise picked up by the cable gets added directly to the signal.
A balanced connection, on the other hand, uses a cable with three conductors, typically found in cables with XLR or TRS (Tip-Ring-Sleeve) ¼-inch plugs:
Here’s how the three conductors work together:
The original audio signals arrive completely out of phase (Hot is +, Cold is -). When the differential amp subtracts Cold from Hot, the audio signals reinforce each other: (+Signal) - (-Signal) = +2.
The noise signals, however, arrived in phase (identically) on both wires. When the differential amp subtracts the Cold noise from the Hot noise, they cancel each other out: (+Noise) - (+Noise) = 0.
The result? The unwanted common-mode noise is rejected, while the original audio signal is effectively doubled in level.
If the math isn't intuitive, think of it this way: Balanced input instantly flips the polarity of the signal arriving on the Cold wire (both the inverted audio part and the noise part). This action brings the originally inverted Cold audio signal back in phase with the Hot audio signal. However, since the noise was identical on both wires to begin with, this flip puts the Cold noise perfectly out of phase with the Hot noise. When the receiver combines the Hot signal with this polarity-flipped Cold signal, the two in-phase audio signals add up, while the two out-of-phase noise signals cancel each other out.
Think about connecting your mixing console at the Front of House (FOH) position to the main power amplifiers or powered speakers on stage. This often involves long cable runs. Running unbalanced cables over long distances would almost guarantee significant noise pickup. That's why this connection is almost always made using balanced cables (XLR or TRS). The balanced connection's ability to reject noise picked up over these long runs is essential for professional, clean sound.
An electric guitar typically outputs an unbalanced, high-impedance signal through a standard ¼-inch TS jack. For the relatively short cable runs usually found between a guitar and a pedalboard or amplifier (say, up to about 5-6 meters / 15-20 feet), this is generally fine. The amount of noise picked up isn't usually problematic.
However, if you do need to run a guitar signal over a much longer distance (e.g., from the stage to a mixer far away), noise becomes a concern, as does signal degradation due to the high impedance. This is where a DI (Direct Injection) box becomes indispensable. A DI box converts the guitar's unbalanced, high-impedance signal into a balanced, low-impedance signal (usually via XLR output), making it suitable for long cable runs and connection to mixer microphone inputs, effectively preventing noise pickup.
