Reduce a Computer’s Audio Output Line Hum

đź“… August 30, 2016
isolator“Why do I hear a faint hum from my computer’s audio output?”

Computers are electrically noisy environments, and all of those wires and fans and whatnot operating at various frequencies can have unpleasant side-effects on a computer’s audio output.

If you enjoy listening to music played from your computer and if you use the computer’s analog stereo outputs (the 3.5mm line out jack) to connect to an external amplifier or receiver, then you have no doubt encountered the low-frequency hum effect.

Not a mere hiss due to a noisy sound card, but a low hummmmmmmmm that is heard consistently whether or not audio is playing and regardless of the volume level.

This can happen with any home audio equipment, not just computers. Often, it is caused by a ground loop, and the best way to reduce or nearly eliminate this hum is to electrically isolate the audio output (from the computer) from the audio input of the receiver/amplifier.

A simple device to use is a 1:1 isolation transformer, also know as an audio ground loop noise filter. These are small, inexpensive devices that plug between the computer and the receiver to reduce — if not eliminate — the low-frequency hum that can be annoying to listen to through earphones or speakers.

Several are available, and I have used the BOSS Audio B25N ground loop isolator noise filter. These are often found in automotive sound systems to reduce motor interference, but they work just as well with computers and home audio equipment.


B-25N Ground loop isolator shown with extra RCA connections. One side is stereo audio in, and the other is stereo audio out. Despite the shiny appearance, it is made of plastic, not metal.

The B25N has two sets of RCA phono jacks for stereo in and stereo out. You will need an extra 3.5mm to RCA cable to connect the isolator to your computer.

Does it work?


This is probably one of the best computer audio improvements around if using analog audio. Any hum is eliminated to almost zero. In many cases, I cannot hear any hum at all. Any noise depends upon the quality of the sound card or motherboard audio.

Sound quality is almost as pure as it gets for analog stereo signals.

What about digital audio?

An isolator is only needed for analog audio. Since SPDIF optical and coaxial connections are digital, they are immune to line noise and ground loop hum, so this will have no effect.

Pay attention to where you place the isolator

Transformers are electrical devices that transfer electrical current from one coil to another via electromagnetic induction. Current flowing through one side of the transformer induces current in the opposite side. Because the two coils have no direct contact with each other, they are electrically isolated, and this isolation eliminates the ground loop hum effect.

However, this is also a weakness for home audio because any other source of electrical induction can influence the “clean side” of the transformer. If you use an audio isolator but place it too close to your computer (on top or behind it, for example), then other stray electrical noises from the computer will find their way into the signal again. It is the same effect as placing an AM radio next to a computer. Stray signals are emanating, causing electrical disturbances to nearby devices.

To mitigate this effect, place the isolator at least 20cm away from a computer or other noisy sources, such as fans.


If you use analog audio and are experiencing line hum, then an audio ground loop isolator will certainly improve the resulting sound quality by reducing the hum and noise.

It is low-cost, and it improves a computer’s analog audio output significantly. In fact, I would consider this device to be more important than a high-end sound card without using an isolator. Of course, when an isolator is combined with a high-end sound card, then analog stereo output is almost as good as it gets.

And yes, it is 100% compatible with Linux!

Highly recommended.





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