How to Remove Hum From Audio

Electrical hum - that steady low drone or buzz sitting under a recording - is one of the cleanest problems to remove, because it lives at a fixed, predictable frequency: 50 Hz in most of the world, 60 Hz in North America, plus a stack of harmonics above it. A dehum process or a set of notch filters can carve out those exact frequencies and leave the voice almost untouched. The buzz vanishes and the recording stays natural. The only catch is targeting the right frequency and its harmonics, not guessing with a broad EQ cut.

Why hum is easy to remove

Hum comes from mains electricity leaking into your signal, so it inherits the frequency of the power supply. That is either 50 or 60 Hz, and crucially it also appears at whole-number multiples - 120, 180, 240 Hz and up for a 60 Hz system, or 100, 150, 200 Hz for a 50 Hz one. Those multiples are called harmonics, and they are what give hum its buzzy edge rather than a pure tone.

Because all of that energy sits at known, narrow frequencies, you can remove it with surgical notches that barely touch the wideband voice around them. This is the opposite of broadband hiss, which is spread across the whole spectrum - see how to remove background noise from audio for that case. Match the tool to the noise: notches for hum, profile-based denoise for hiss.

Removing hum: dehum or notch

The easiest route is a dedicated dehum process. You tell it the base frequency - 50 or 60 Hz - and it automatically places notches at that fundamental and all its harmonics, then pulls them down together. Modern dehum tools can even track slight drift and adapt the depth per harmonic, so you remove the buzz without gutting the low end of the voice.

If you are doing it by hand, place a narrow, deep EQ notch at the fundamental, then more notches at each harmonic above it. Keep them narrow - a wide cut removes voice along with hum. Sauce's Audio Repair handles the fundamental and harmonics for you in a single pass, which is far faster and more accurate than chasing each harmonic manually.

How to find the right frequency

If you are not sure whether it is 50 or 60 Hz, your location is the first clue: North America, most of it 60 Hz; most of Europe, Asia, Africa and Australia, 50 Hz. To confirm, solo the hum in a quiet gap and try each - the correct fundamental makes the buzz drop away completely, the wrong one only dents it. A spectrum analyzer makes it obvious too: hum shows as a row of evenly spaced spikes, and the spacing tells you the fundamental.

Ground loops and where hum comes from

The most common source is a ground loop - when two pieces of gear are connected to power through different ground paths, a small current flows between them and shows up as hum. Other culprits are unbalanced cables running near power supplies or lighting, cheap or damaged cables, dimmer switches, and phone chargers or laptops on the same circuit. The buzz is being induced into your signal before it is ever recorded, which is why removing it after the fact is a repair, not a cure.

It helps to know the difference between hum and buzz, because they hint at the cause. A smooth, low drone dominated by the fundamental usually points to a ground loop. A harsher, buzzier tone rich in high harmonics more often means a cheap unbalanced cable acting as an antenna, or a nearby light dimmer. Either way the removal is the same - notch the fundamental and harmonics - but the diagnosis tells you what to change so it does not come back on the next take.

What can and cannot be fixed

• Clean, steady hum at a stable frequency - removes almost perfectly. The ideal case.
• Hum with many strong harmonics - still very fixable; just make sure the tool addresses the harmonics, not only the fundamental.
• Hum that drifts or wavers in pitch - harder, because static notches miss a moving target. An adaptive dehum that tracks the drift does better.
• Hum plus broadband noise - remove the hum with notches first, then denoise the remaining hiss separately. Two problems, two tools.

A quick step-by-step

• Identify the fundamental - 50 or 60 Hz - from your location, then confirm by ear in a quiet gap.
• Apply a dehum process set to that frequency so it notches the fundamental and its harmonics together.
• If doing it manually, place narrow notches at the fundamental and each harmonic, keeping them tight.
• Check that the low end of the voice still sounds full - if it thinned out, your notches are too wide.
• Denoise any remaining broadband hiss separately after the hum is gone.

Hum is usually one item on a longer list, so slot it into the wider order in how to fix a bad vocal recording - dehum comes early, right after declipping.

Prevention beats repair

Stopping hum at the source is easy once you know the causes. Use balanced cables and keep audio leads away from power cables and adapters. Plug all your audio gear into the same power strip so they share one ground. Keep phone chargers, laptops and dimmers off the audio circuit. If a ground loop persists, a proper ground-loop isolator on the offending connection removes it electrically, so you never have to notch it out afterward.