How to Clean Noisy Hums From Video and Sound Effects

The most common audio related request that I receive from producers and video editors is to remove an annoying hum or rumble from a finished piece of video, whether a short film, corporate piece, web commercial, etc. It seems that often budgets do not account for a sound person on location during the shoot to ensure high quality audio recording and videographers generally opt to plug in a few mics and wing it during the shoot. As a result, dialog is often difficult to hear and/or competes with background hums from the environment, i.e., the dreaded air conditioner or other piece of industrial equipment. The same noises often need to be eradicated when recording and mixing sound effects or other sound design elements for video.

While there is a plethora of software pluginsĀ music & sound design such as SoundSoap, Audacity, and Soundforge that provide noise reduction algorithms to help fix the offending noise, these all require a bit of study and time that may be impossible under tight deadlines. I’ve had requests to clean up audio for projects due for uploading in the next few hours. Sometimes I’m available to help and sometimes not. For those of you who find yourself plagued by the Beast of Hum from an air conditioner, under a tight deadline, and without audio support, here are a few quick and dirty strategies available readily available in audio/video software that won’t solve damaged audio completely (nothing will), but may certainly ease your suffering:

EQ or Equalization: Trim down the offensive hum

Single Band EQ plugin: The first step in audio sweetening is to remove unwanted noise. Since a hum or rumble generally resides around 60 Hz, immediately use a Single Band Equalizer, generally named Low Cut (see jpeg below), to cut out all frequencies below 120 Hz. You can usually cut out all frequencies below 100 to 120 Hz without adversely affecting dialogue.

Parametric Equalization plugin: Notch targeted areas

Using a parametric equalizer, in Logic Pro called a Channel EQ (see jpeg below), choose a Notch Filter to notch out the frequency at 60 Hz and its octaves at 120 Hz and 240 Hz (if you’ve already used the Low Cut at 120 Hz then the notch at 60 Hz will be irrelevant). This will remove some of the offending hum without affecting the frequencies that surround it. A notch filter uses a high Q, which is essentially the width of the equalization. A higher Q means a more narrow EQ target. Therefore for notch filtering you want to set your Q at 100 if doing it manually, and your decibels at -96, which reduces the volume of the undesired frequencies to zero without affecting the frequencies below and above it.

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