Audacity is a free software program that can record and edit audio files. It supports all major audio formats. With it, you can convert files from format to format, such as from WAV to MP3. You can also use it to reduce background noise in audio files.
To reduce background noise in Audacity, first open your audio file in the program. As with all discovery, please make sure to always work with a copy of the discovery file and never the original.
Select a section of the audio containing only the noise that you want to reduce or remove. Try the beginning or the end of your recording or look for a good pause somewhere in your audio file. The key is to select an area with minimal activity. On the file this looks like a flat line. Select enough of the audio to get a good analysis of the noise. Figure 1 below shows what this minimal activity looks like:
Figure 1.
Now go to the Effect menu followed by Noise Removal and Repair and select the Noise Reduction… option. Then click on Get Noise Profile (See Figure 3 below). This will close the dialog box and create a sample of your noise. Audacity uses that sample to analyze and extract the noise from your file.
Figure 2.
Figure 3.
Now select the entire timeline of your audio file by double clicking anywhere on your audio file. You will see a yellow box around your audio file as shown on Figure 4:
Figure 4.
Go back to the Effect menu\Noise Removal and Repair and select the Noise Reduction… option again. There are three adjustable settings that you can use to fine-tune your noise reduction. Each of these controls affects the way in which the noise is reduced. (see Figure 5 below)
Figure 5.
Raising them too high will remove more noise but will also diminish your audio quality. Setting them too low will keep more of your desired audio quality but it can also retain more noise. Keep these things in mind and adjust the levels until the file sounds better to you.
Noise reduction (dB): This setting reduces the identified noise in decibels.
Sensitivity: This controls how much of the audio is considered noise. Setting it too low can result in higher frequency distortions in the audio. Try to set this to the lowest level that achieves a satisfactory amount of noise removal without introducing distortions.
Frequency smoothing (bands): This control helps smooth out possible distortions that occur from increasing the frequency range of the noise being reduced. A higher setting will make your audio file less clear so keep it low or even off.
Try the default settings first. These tend to work well for basic noise removal. If this doesn’t help, try playing with the Noise reduction and Sensitivity settings. You can click on the Preview button to listen to the area that you selected previously in Figure 2 above, to see if the noise has been reduced.
Another way to hear the effect of your settings is to listen to only the parts of the noise signal being removed. You can do this by selecting the Residue option in the Noise setting as shown on Figure 6. below.
Figure 6.
Once again, play with the Noise reduction and Sensitivity settings and listen to the audio by clicking on the Preview button. This is useful for finding the optimum settings that do not damage the audio. If you can hear recognizable bits of the desired sound in the residue, it is likely that you have set the noise reduction or sensitivity too high. Once you’re done, change the noise setting back to Reduce and then press OK. When you are satisfied with the result, export the audio from the File menu. Give it a new name—do not overwrite the original file.