sábado, 7 de maio de 2011

How To Remove Ambient Noise From Your Audio Files Using Audacity

How To Remove Ambient Noise From Your Audio Files Using Audacity: "

how to remove background noise from audioIf you’re a little bit musical or you make your own podcasts, you’ve probably noticed that sometimes your recordings can sound a little annoying due to the background noise captured in the recording process. This white noise is not always easy to remove, but can be minimalised by the use of free tools and a little know-how.

Audacity is a free program available for Mac, Windows and Linux, so most people should be able to download this and use it to clean up their recordings. Today we’ll take you through a few simple steps you can use on all recordings to remove background noise from audio.

Install Audacity

When you’ve downloaded Audacity, you’ll notice that it’s able to be used to import or record music and vocal tracks and can be used to mix tracks together for other purposes. This makes it very useful to musicians and podcasters alike, whether you are an amateur or a professional. It’s very easy to isolate sections of each individual track and use the editing features to remove the ambient noise in the background.

Import Or Record Audio

Either import the audio file you wish to clean up, or use Audacity as the recording tool. In Mac you need to go to Project > Import Audio, whereas in Windows you’d use File > Import > Audio.

how to remove background noise from audio

Isolate A Quiet Moment

After importing, you’ll see the tracks of the audio file as separate lines in Audacity. This shows the waveform of the track. Flat sections are quiet while big vertical lines indicate the noisy sections.

noise removal help audacity

Zoom in until you can find a moment where there was no deliberate sound in the track (the flattest bit you can find), such as when you paused for a moment. Go to View > Zoom In. Then highlight the flat section by clicking and dragging with your mouse across that part of the track. Audacity suggests this selection shouldn’t be longer than a half a second.

noise removal help audacity

This will isolate a moment where all you recorded was the ambient background noise. By letting Audacity know precisely how much background noise there was, it can calculate how to remove it from the rest of the track.

Step 1 – Get Noise Profile

Once you’ve selected the quiet part of the track, go to select Effect > Noise Removal.

noise removal help audacity

This opens up a dialogue to remove the noise. You’re performing Step 1 here, so click on “Get Noise Profile” and the dialogue will disappear. You can do this again at any time and it will overwrite the previous selection. What happens next is a little confusing, as it has already acknowledged your quiet section of your audio track and simply shut the window on you.

how to remove background noise from audio

Step 2 – Apply Noise Reduction

Now Audacity needs to know which parts of the audio track you want to apply the noise reduction to. Most likely, you’ll want to apply the reduction to the whole project, so click CTRL-A or CMD-A to select all. If you want to select just a portion of the track or just one track, place your cursor at the start of your desired selection and go to Edit > Select > Cursor to End. Then, to remove ambient noise from the selection, go to Effect > Noise Removal again.

We’ve done step 1, so skip to step 2 now. Move the slider to indicate how aggressively you want Audacity to strip the background noise from your track. Many people tend towards the lower end, since stripping out too much sound can make voices sound quite tinny and weird. You can preview the sound or go straight to “Remove Noise“. If you don’t like it later, you can undo it. Make sure you listen to it before you go on to make more changes.

When you view your tracks, you should be able to see that the peaks are not quite as high, and the flat sections are far flatter now.

If you’re dealing with a special case, such as removing noise from cassette audio, take a look at the full Audacity wiki page on noise removal. There’s some great tips.

See also these great articles on Audacity:

Image Credit: ShutterStock

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