Hum and Buzz in Live Sound: Identifying and Eliminating Noise

Hum and buzz contaminate audio signals with unwanted low-frequency noise, typically at 60 Hz (50 Hz in some countries) and harmonics. These problems plague live sound systems drawing power from imperfect electrical systems while connecting multiple ground references. Understanding the causes enables effective solutions.

Identifying the Noise Type

60 Hz (or 50 Hz) hum sounds like a pure tone. This frequency matches the AC power line frequency and indicates ground loop or power-related issues.

120 Hz (or 100 Hz) buzz contains more harmonics and sounds rougher than pure hum. This often indicates poor filtering in power supplies or severe ground loop issues.

High-frequency buzz or whine suggests RF interference, digital noise, or lighting dimmer issues. These require different solutions than traditional ground-related hum.

Understanding Ground Loops

Ground loops form when equipment connects through multiple ground paths. Current flowing through these parallel paths creates magnetic fields that induce hum in audio signals.

The classic scenario: a guitar amplifier plugged into one outlet and a DI box sending to a mixer plugged into another outlet. Two ground paths exist—the audio cable and the building wiring—creating a loop.

Breaking the loop eliminates the hum. This means interrupting one of the ground paths without creating safety hazards.

Ground Lift Solutions

DI box ground lift switches disconnect the cable shield from ground at the DI. This breaks the loop at a safe point without affecting safety ground connections.

Try ground lift first when DI’d instruments hum. This simple fix solves most instrument-to-PA ground loop problems.

Isolation transformers break ground connections through magnetic coupling rather than direct connection. DI boxes with transformers provide inherent isolation.

Single-Circuit Connection

Connecting all audio equipment to the same electrical circuit eliminates ground potential differences. Same circuit means same ground reference.

Use extension cables from a single outlet or power strip rather than spreading equipment across multiple venue circuits.

This approach may not always be practical—available circuit capacity and outlet locations may limit options. But when possible, single-circuit connection prevents many ground problems.

Cable-Related Issues

Damaged cable shields allow interference to enter. Check cables with intermittent or persistent hum issues; frayed shields or broken connections cause problems.

Long unbalanced cable runs pick up more interference than short runs. Keep unbalanced cables (instrument cables) as short as possible.

Balanced cables (XLR) reject interference through common-mode rejection. Use balanced connections wherever possible for noise immunity.

Running audio cables parallel to power cables induces interference. Cross power cables at 90 degrees; maintain separation for parallel runs.

Dimmer and Lighting Noise

Theatrical dimmers create electrical noise that can enter audio systems. The chopped waveform from SCR dimmers generates harmonics throughout the electrical system.

Isolating audio and lighting on separate circuits helps but may not completely solve dimmer noise in heavily contaminated venues.

Power conditioners with filtering can reduce dimmer noise on audio equipment. Units with effective noise filtering clean up power-line-carried interference.

RF Interference

Radio frequency interference from radio stations, cellular towers, or other RF sources can demodulate in audio equipment, creating audible noise.

Ferrite chokes on cables block RF conducted into equipment. Clamp-on ferrites installed near cable ends can reduce RF problems.

Shielded cables and proper grounding help reject RF pickup. Unshielded cables or poor ground connections increase susceptibility.

Troubleshooting Process

Isolate the source by muting channels one at a time. When hum disappears, the last-muted channel contains the problem source.

Check that channel’s signal chain: source equipment, cables, DI boxes, and connections. Apply ground lift if available.

If ground lift does not help, try isolating power connections. Move equipment to the same circuit as the mixer.

For persistent problems, substitute components to identify the faulty element. A different DI, cable, or even instrument may resolve the issue.

Equipment-Specific Issues

Computer audio outputs often cause ground loops. USB isolators or audio interfaces with ground isolation address computer hum.

Video equipment sharing connections with audio creates ground loops. Video ground isolators prevent ground current through video cables.

LED lighting, while not creating dimmer noise, can produce RF interference. LED drivers may create electrical noise in different frequency ranges.

Prevention Strategies

Design systems with ground management in mind. Plan power distribution and signal routing to minimize ground loop potential.

Quality equipment with proper grounding and filtering resists noise better than cheap alternatives.

Test systems before critical events. Discover and solve hum problems during setup rather than during performance.

Document solutions for recurring venues. What worked before will likely work again.