How to eliminate noise
Grounding, cables and DI boxes: the step-by-step diagnosis for a silent system.
About this guide
Noise is the problem that generates the most questions — and the one that gets solved worst. It's almost always attacked by blind substitution: swap a cable, try another socket, and at some point it goes away without anyone knowing why. When it comes back on another setup, you start from zero.
This guide treats it as a diagnosis instead. First you classify the noise by how it sounds, because each type has a different cause; then an isolation protocol pinpoints the exact spot in the chain where it's getting in. Nine chapters that go from the mechanism (balanced lines, ground loops) to the practical six-step protocol, which DI box or line isolator solves each case, and the six setups that come up most often. Includes a one-page checklist to print.
One warning goes first: the shortcut of lifting a unit's safety ground to kill a hum does work, but it removes the electrical protection and has caused deaths on stage. That solution appears nowhere in this guide.
What you'll find inside
- 1 Noise isn't one thing: classification by audible symptom
- 2 Balanced vs. unbalanced: why one line rejects noise and another doesn't
- 3 Ground loops: the mechanism and the three real fixes
- 4 What you never do: the safety ground is off-limits
- 5 Diagnostic protocol: isolate the problem in six steps
- 6 DI boxes and line isolators: which purchase solves each case
- 7 The setups that keep coming up: six real cases and their fix
- 8 Noise that isn't electrical: hiss, self-noise and digital faults
- 9 The soundcheck for noise: catch it before the audience arrives
- 10 Diagnostic checklist to print
Listen to the samples
Compare your case against these references: recognizing it by ear is far more reliable than working from a description.
Frequently asked questions
Why shouldn't I lift the safety ground to kill the hum?
Because, although it removes the noise instantly, it also removes protection against an insulation fault and leaves the chassis silently live at mains voltage. It has caused deaths on stage. The correct fix is to break only the signal ground with a DI box or a line isolator, while keeping each unit's safety ground intact.
How do I know whether the noise comes from my gear or from the electrical installation?
Listen to how it sounds and when it appears. A low, steady 50 Hz hum is usually a problem inside the system (a ground loop or an unbalanced run). A harsh, metallic noise that changes as you dim the room lights points to the lighting or the venue's wiring. If it stays identical with every light off, look inside the audio system.
What's the difference between a DI box and a line isolator?
Both carry a transformer that electrically separates input and output and breaks the ground loop. A DI box also matches impedance and converts to balanced: it's for connecting an instrument to the mixer. A line isolator doesn't match impedance and sits between two devices already working at line level (computer–interface, mixer–amp, video–sound).
Is the guide free?
Yes. We send it to you for free in exchange for your email. It also includes the audio samples of the six types of noise so you can identify yours by comparing it against a reference.