Balanced transmission is primarily used in professional environments to enable long-distance signal transmission, featuring standardized interfaces for consistent input and output impedance. This method typically uses three wires—positive, negative, and ground—to transmit a single audio channel. It has become the standard in professional recording equipment. Later, Japanese manufacturers introduced this interface into consumer products. The core of balanced transmission is push-pull amplification, which effectively suppresses common-mode interference. In contrast, unbalanced transmission relies on single-ended amplification, where the ground wire plays an essential role in signal transfer.
Most balanced headphones use four wires: L+, L-, R+, R-. Unlike traditional earphones that use a single ground (LR GND), each earphone in a balanced setup is driven by a BTL (Bridge-Tied Load) configuration inside the player, rather than OTL or OCL modes. I've encountered balanced headphone interfaces with four-core Canon jacks, but have never seen four-core 3.5mm or 2.5mm jacks. From an auditory perspective, when well-designed balanced analog signals are amplified, they offer improved dynamics, speed, soundstage, and signal-to-noise ratio compared to unbalanced signals, which tend to sound softer and more confined. However, poorly designed balanced systems can produce harsh, unnatural sound, often worse than regular unbalanced outputs. For most portable devices, a balanced output is essentially meaningless unless it's a professional field recorder.
Many who have used audio editing software have performed "silencing the accompaniment." Understanding this principle gives you a solid grasp of the basics. Essentially, one of the stereo channels is inverted and combined with the other, causing identical waveforms to oppose each other—one going up, the other down.
[Image: Interpretation of the difference between balanced and unbalanced CD playback]
[Image: Interpretation of the difference between balanced and unbalanced CD playback]
In true stereo recordings, instruments are usually placed left and right, while vocals are centered. When one channel is inverted and superimposed, the centered vocal waveform becomes opposite, canceling out the peaks and valleys. Ideally, this results in complete cancellation, though in real recordings, some residual remains (the red part represents the remaining centered vocal, which is already minimal).
[Image: Interpretation of the difference between balanced and unbalanced CD playback]
[Image: Interpretation of the difference between balanced and unbalanced CD playback]
For left or right instruments, since their waveforms aren't exact opposites after inversion, they are less affected, but some elements—like centered percussion with little reverb—may disappear entirely. Thus, silencing the accompaniment actually results in a mono signal, which may not sound great.
The XLR or TRS balanced signal works on this principle. One of the three cores carries the normal-phase signal, another the inverted-phase signal, and the third serves as a shared ground. Upon reaching the receiving device, the inverted signal is flipped back to its original phase and combined with the normal one, canceling out any interference picked up along the way. This allows for cleaner, longer-distance transmission compared to two-wire unbalanced systems. That’s why professional audio gear typically uses balanced interfaces.
This explanation covers a single-channel audio signal. A balanced system splits the signal into two parts, inverts one, and sends both through the same three-core cable. Any interference affecting both signals is similar, so it cancels out when recombined at the receiver. The same logic applies to stereo or surround sound, with one set of cables per channel.
Additionally, it's important to note that two-channel does not equate to stereo—stereo requires two channels—but multi-channel doesn't mean surround sound either; surround sound must involve multiple channels. If my understanding is incorrect, feel free to clarify.
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