Audacity Tutorial – Compression Using the Chris’s Dynamic Compressor Plugin

Posted August 21, 2015 by Shaun

Audacity is a powerful, free audio editor that’s been indispensable to podcasters since the inception of the medium. For someone new to audio production, however, it can be confusing and intimidating. This series of tutorials is aimed at the podcaster or amateur broadcaster who doesn’t want their great content obscured by bad audio quality.

Please note that these tutorials don’t avoid jargon. It’s everywhere in Audacity itself, so avoiding it seems counterproductive. Instead, I try to define as many terms as possible from the perspective of someone with little- to no background in audio production.

Tutorials in this series

» Compression using the Chris’s Dynamic Compressor plugin
» Noise Reduction (formerly Noise Removal)
» My Plug-Ins Aren’t Showing Up!
» Common Usage Scenarios for Noise Gate (currently in progress)
» Useful Equalization Presets (currently in progress)
» Increasing Levels, Avoiding Clipping with Peak Limiter (currently in progress)
» Suggested workflow: Poor-quality original recordings (currently in progress)
» Suggested workflow: Mid- to high-quality original recordings (currently in progress)


Introduction

To follow along with this tutorial, you’ll need to download a third-party plugin called Chris’s Dynamic Compressor. The plugin and an excellent installation walkthrough can be found here, thanks to Daniel J. Lewis’s excellent and highly recommended TheAudacityToPodcast.com.


What is compression?

The overgeneralized way of explaining compression is that it raises the volume of quiet things and lowers the volume of loud things. The advantage of applying compression is that everything will tend towards a consistent volume, which is listener-friendly; no one wants to strain to hear certain things and then have their eardrums blown out during subsequent loud sequences.

Speaking directly to the name of the plugin discussed in this tutorial, the term “dynamics” refers to the relationship between the quietest and loudest part of a given piece of audio. If that ratio is high, then there is a large difference between the quietest and loudest parts. For the comfort of your listeners, you want to lower, or “compress” the dynamics.


How can I tell if I need compression?

compression-01

There are two issues here. One is that A is too quiet. A more optimal level would be something like B, which looks to peak at around -5 dB.

The second issue is that the dynamic range is very high. In other words, there is a large difference between the softest part- A– and the loudest part, B.


Applying Compression Using Chris’s Dynamic Compressor

Chris’s Dynamic Compressor is listed in the Effects menu as “Compress dynamics 1.2.6…” Select it and you’ll be presented with this dialog.

nerd1

For simple voice recordings like narration or podcasting, it makes sense to use a compression ratio and maximum amplitude of 1.000. Compression ratio at 1.000 will keep levels pretty consistent across the board, and maximum amplitude means at 1.000 means that the clip will be loud. Many podcasts make the mistake of releasing at a much lower volume than a typical broadcast.

I typically use a compression hardness of 0.650 because this retains a small amount of dynamic range. Adjust this number to your liking. Anything between 0.250 and 0.750 is probably appropriate. Too low of a number and soft speaking may not become loud enough, while too high a number can mean that sounds like taking a breath are distractingly loud.

The floor is the point at which the compressor will treat sound as unwanted. -32.00 dB is a good starting point. A higher number, like -24.00 dB, may cause the compressor to accidentally get rid of soft speaking, or desirable organic sounds like breath-taking. A lower number, like -48.00 dB, may result in an excess amount of leftover noise.

Noise gate falloff is how aggressively the compressor will reduce sounds that fall beneath the floor. In this example, our floor is set at -32.00 dB, so anything quieter than -32.00 dB will have falloff applied.

Falloff, in this case, is just a fancy word for reduction of volume, and it’s measured here in factors. For example, let’s say we’ve got audio that’s -33.00 dB (in other words, 1 dB below our floor). The compressor will see this and consult the noise gate falloff setting to determine what to do. If we’ve entered 2 as our noise gate falloff, the compressor will reduce this audio by a factor of 2, for a result of -66.00 dB.

compression-02

Here’s an example of what the waveform from the beginning should look like, after a good round of compression. Note that all peaks are around -5 dB, which is a great volume, and that the vast majority of peaks occur at between -20 and -5 dB, which is a nice, tight range.


That’s it for basic compression. If there’s anything else in the post production or editing processes that you’d like me to cover, please feel free to leave a comment.

If, like a lot of podcasters, you’re too busy generating content than to mess with Audacity settings, get in touch. For a nominal fee, I’m happy to complete a round of post production and provide a detailed write-up of what I did, so you can do it yourself from then on.


Next: Audacity Tutorial – Noise Reduction (formerly Noise Removal) →