How to Use the Compressor in Audacity
Compression is a useful tool to reduce the dynamic range in your audio files so the overall volume level is even throughout the episode. Without compression, your listeners might hear a blaring loud intro followed by an interview so quiet they have to adjust their volume to hear it.
In this tutorial, you'll learn how to apply the compression effect to your Audacity files, so the audio sounds even, round, and easy on your listener's ears!
Download Audacity (Mac, Windows, Linux)
When should you use audio compression?
Nearly every episode you work on can benefit from adding compression because all audio recordings have portions that are too quiet and others that are far too loud. Sometimes podcasters record a voice over that is much louder compared to their interview track, or outro, for instance.
Adding compression in this scenario will make the volume of the voice over stay within the dynamic range of other clips within the episode. Now that you have an idea of when you'd use the effect, let's take a look at how to apply it.
Applying the Audacity Compressor effect
To apply compression to your clips, your first have to select the audio where you want to apply the effect.
You can press the Select button on the left off the track to select a portion of the waveform or use the keyboard shortcut Cmd + A to select all the audio tracks.
From there, go up to the Effect tab > Compressor. Here, Audacity gives you several levers you can pull to hone in your compression. We'll break down what each of these features do so you get a basic understanding of how they work.
The line graph
When you open the Compression window, you'll see a blue line graph depicting the dynamic range compression effect. The graph line only changes as you adjust the Threshold and Ratio — it won't reflect the changes you make with any of the other levers.
The horizontal axis at the bottom shows the input dB level, and the left vertical axis shows the output dB level.
The first selection is called Threshold, which is the point when you want Audacity to apply compression. How loud do you want your audio to get before the compression starts?
Remember, compression happens to the loudest parts of our audio. Selecting -12 dB means any parts of your audio that are louder than -12 will get compressed (we suggest leaving the Threshold at -12 dB.)
The second thing you can adjust is the Noise Floor, which allows Audacity to tell the difference between when you're speaking and when there are gaps in your words or silent parts of your audio. Essentially, this setting prevents Audacity from taking the wrong portions of audio and boosting it by accident.
Let's say you have ambient noise or silence in between your clips. Increase the Noisefloor level to prevent Audacity from making that ambient noise even louder.
Ratio determines how much you want Audacity to compress your audio. Adjusting the Ratio too much will make the audio sound over-compressed and monotone. But if you don't modify the Ratio enough, it won't sound like you did anything at all.
Just remember, the higher the Ratio, the more it's compressed; the lower the Ratio, the less it's compressed.
Attack Time & Release Time
The Attack and Release time refer to how quickly you want Audacity to respond to changes in volume. Let's say you're speaking in a normal voice and then laugh or say something extra loud. How quickly do you want Audacity to identify that peak in your volume and compress it?
If you want it to react very quickly, you lower the Attack Time; if you want it to take a little longer before applying compression, use a longer Attack Time.
The Release time is similar to Attack Time, but it's on the back end. Let's say your audio has gone below your Threshold. Maybe you spoke very loudly for two or three seconds, and then you go back to a normal tone that's beneath the Threshold. In this example, we have the Threshold set at -12 dB; the Release time tells Audacity how long until you want it to stop compressing that audio.
It's best to leave each lever at the default setting, listen to what it sounds like, and make tweaks from there. If you mess with the default settings too much, you can quickly get into a situation where you've messed up your audio and aren't sure how to get it back.
Summary: Attack Time tells Audacity to start applying compression, and Release Time tells it to stop.
Other Compressor settings
Make-up gain for 0 dB after compressing
There are two checkboxes you want to know about. The first one is Make-up gain for - dB after compressing. When you apply compression to an audio track, the volume will be lower, and sometimes too low. Selecting this box means Audacity is going to amplify your audio and bring the softer parts back up so it's at a listenable, editable level of 0 dB.
Compress based on peaks
The other option you have is Compress based on peaks. Here, Audacity looks at the peaks in your audio and uses that value to compress, verses your Threshold floor setting. We suggest leaving this box unchecked.
You can also pair the Audacity Compressor effect with the Limiter effect, which serves as a hard brick wall, saying anything louder than this particular decimal level is cut off at the knees.
We don't suggest bothering with this unless you're having issues with clipping (audio distortion). Just know the effect is available to you if you need to continue to fine-tune your compression settings beyond what we've covered.
How to avoid over-compressing
You can over-do any audio editing effect, even compression. The good news is your listeners probably don't know a lot about audio editing or care about what effects you use. All they know is what sounds good to their own two ears.
Compression should make your audio sound more even, professional, and warm. But if your final product sounds distorted, too loud, harsh, you might have over-done the effect. If portions of the audio are too quiet, you might not have added enough of the effect.
It can help to save your original audio file so you can compare it to the final product. Like editing a photo or video, hearing the raw original can help you discern the final product's quality.
Alternative Compressor: If you want to try your hand at a different kind of Compressor, Chris's Dynamic Compressor is a free compressor plug-in that helps to even out abrupt changes using a "lookahead" feature that anticipates future volume changes. You can download the Compressor here and watch this tutorial to learn how to use the tool.
Preview your settings
If you want to preview what this would sound like, you can click the Preview button to listen to six seconds of playback (or longer based on your settings). If you're happy with the amount of compression, click Ok!
Now, Audacity will analyze your file and apply your compression settings. It will apply gain reduction to loud parts and amplification to others to even out the overall volume level and give you a well-rounded file!
More Audacity tutorials
Compression is an important effect for podcasters to know how to use, and adding the effect is an easy way to make your episodes sound more professional. If you want to learn more about how to use Audacity to edit your own podcast, these guides can help you get more comfortable with the tool!