Noise and Hum

Hiss comes from the circuit, hum from the grounding. Separate them before you treat either.

Related

Noise FloorSignal-to-Noise RatioOrgan

The problem

In quiet passages, hiss and hum arrive before the music. Hiss comes from circuits and gain; hum from power and grounding. Their causes differ, and so do the cures.

Signal chain

Noise accumulates along the chain. The microphone picks up the room and electromagnetic fields, the preamp amplifies its own noise floor with the signal, and the converter adds more. Hum usually comes from a ground loop at 50 Hz with harmonics that shift with cables and outlets.

Placement and settings

Set gain from the loudest passage so peaks land near -12 dBFS, and do not make up level later. Keep microphone cables away from mains cables and displays, and plug every device into the same outlet strip. When hum appears, unplug inputs to find the source, then fix it with balanced wiring and correct grounding instead of EQ.

What to listen for

In a silent passage, raise the monitor and hear whether hiss grows with gain. Change the power outlet and hear whether the hum moves. Its harmonics often land in the low voice range, where they can be mistaken for too much body.

Common misconceptions

• Noise means a bad microphone → gain staging and grounding are more common.
• A denoiser fixes everything → it also eats the tails of soft notes.
• Hum means broken gear → most hum is a ground loop.

Sources

• Ballou, Handbook for Sound Engineers, grounding and shielding chapters
• AES Convention paper on hum, ground loops and balanced interconnection

Used for fact-checking only; all prose is original.