Removing noise from a recording with Audacity

Do you have a problem with background noise in your audio recordings? If so, I may have the answer.

Now it is obviously better to ensure that your recording environment is as quiet as possible but that it not always possible for a number of reasons. For example, I usually record on a laptop in our family room area which means that I always have the noise of the laptop fans and, during winter, of the central heating boiler pump. I’d never realised that either of these made a detectable noise until I started recording with a condenser microphone.

I tried everything I could to minimise this, by moving the mic as far away as possible, draping stuff with blankets and bedding, but it still wasn’t enough.

Time to call in Audacity, a superb free, open-source audio editor available for most platforms (Linux, OSX and Windows). If you don’t have this installed on your system then go straight to http://audacity.sourceforge.net/download/ and download it now. You will not regret it! If you’re going to want to export to mp3 then grab the installer for the LAME encoder from http://lame.buanzo.com.ar/ while you’re at it.

One of the things Audacity can do is to analyse a section of your recording that is supposed to be silent, build what it calls a “noise profile”, and then subtract the noise profile from the whole track.

Let me talk you through the steps:

  • When recording, ensure that you have at least 2-3 seconds of silence;
  • Open the track in Audacity;
  • Select the silent section of the track;

  • From the menu choose “Effects”, and then “Noise Removal…”;
  • Click the “Noise Profile” button;

  • Now select the section of the track (usually all of it) from which you want to remove the noise;

  • From the menu choose “Effects”, and then “Noise Removal…”;
  • Preview the noise removal, adjust the settings and, when you’re happy with it, click “OK”. So far I have always been happy with the results of the default values, but you need to pay particular attention to the transition between noise and silence, especially where the audio has a gradual decay, like a sustaining guitar;

  • Audacity saves into its own AUP format. If you want any other format then you need to export it by choosing “File” and then “Export…”
  • Now you’re left with an audio track with silent silences. Bliss.

Here’s a before and after example using an acoustic guitar.

Before:
NoiseRemovalBefore.mp3 by davmac

After:
NoiseRemovalAfter.mp3 by davmac

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