You’ve got your recording finished and realized there’s a hum or hiss on one half of the recording. This quick tutorial will walk you how to import your audio into Audacity, split the stereo track and remove the noise.
Start by downloading Audacity from http://audacity.sourceforge.net for your operating system (Mac, Linux or Windows).
Open up Your Stereo Recording in Audacity
In this case we have an mp3 that was recorded from Skype via Piezo from Rogue Amoeba. It records your mic on one channel, and the Skype caller on the other channel.
Single Stereo Track
When we start, we have a single stereo track. You can see in the silence sections on the second track that the center line is thick – that should be a thin line, instead it’s actually noise. We want to remove that noise but only affect the second track.
Split Stereo Track
Tap on the disclosure triangle next to the track name and select Split Stereo Track. This does not exist as an option in the menus up above, only under this disclosure triangle.
Two Mono Tracks
Now that we have two mono tracks, select the track with the noise.
Select a Region of Pure Noise
Hopefully you have a good sample area, but Audacity can do amazing things even if only with a few seconds of data. You can see in the bottom track a grey area that I’ve selected as our noise profile.
Select Effect and Noise Removal…
Click Get Noise Profile
When you click this, the window will go away and it won’t look like Audacity did anything at all, but in fact you’ve just told it, “this is what noise looks like”.
Select the Entire Track
Select entire track, or all of the area where the noise is you want to remove. You should see a yelow border around the track if you’ve selected it properly.
Open Noise Removal Again
Now that you’ve taught Audacity what noise looks like, you can do Step 2 which is telling it to actually remove the noise. The tricky maneuver here is to simply push OK. If you want to go wild and play with the controls, have fun, or just click OK like I do.
Window You'll See During Noise Removal
Nice Clean Audio
Now you can see that in the same gap (and elsewhere) the line is thin, indicating visually that the noise is gone. If you find the audio is distorted as a result of the noise removal, you might want to go back and mess around with those controls.