Tutorial:
The Compression Connection

Brian Peterson
June 2008

To view the tutorial video for The Compression Connection, click here

When you listen to any professional broadcast, you hear audio that sounds clear and natural and has, mostly, the same loudness. This type of audio has narration that cuts through music, sound effects and noise. It just sounds impressive. But while tweaking the audio levels on your latest video project, you just don't seem to be able to get that same great sound. What's the secret?

All professional audio producers use compressors to even out the peaks and valleys of their wavefiles to make their audio sing. And getting you up to speed on just how to do this is the subject of this article.

You can get different results depending on the order in which you apply filters and effects. While personal taste and program material can change this suggested order, we prefer to first reduce the noise, then apply compression/expansion/limiting, do any equalization that's needed and then normalize to -1dB. This order will ensure that your audio maintains the highest signal-to-noise ratio possible and will even provide a little headroom for later sweetening.

To get the best audio, you always want your input signal to be as close to 0dB as possible. But, unlike in the old days of tape, digital recordings will begin to distort when the signal goes beyond 0dB. Since it is nearly impossible to salvage a distorted signal, many of us run our audio levels too low. This forces us to boost the overall signal, along with the noise, during editing. To avoid this, you have three ways to optimize the levels of your audio.

If you are recording a voiceover, use proper mic technique and avoid many of the normal spikes in your signal by not popping your "p's & t's." Simply turn your head away slightly from the mic each time you pronounce these and other plosive and fricative sounds. It takes practice, but it really works. You can further smooth out those audio peaks and valleys by using a hardware audio compressor/limiter when you first record. For the greatest flexibility in post, you can minimize the compressor effect and just use the limiting function to ensure you don't distort your original recording. These units most often come in rack-mount configurations, so they are most convenient to use in a studio setting. The last and perhaps most common solution to optimizing your signal is using the built-in capabilities of your audio editing software or using specialized third-party plug-ins.

If you're not careful, compression can make the quieter parts of your audio, like noise, louder. So it's a good idea to do some noise reduction first. Depending on your audio software, noise reduction may come in several flavors. Hiss-reduction is little more than a bandpass filter that allows or inhibits certain frequencies in the final mix. Others, like click and pop eliminators, automatically find the sharp transients characteristic of these types of noises and reduce or eliminate their presence. But the type that gives you the greatest control will be generically named "noise reduction."

We'll use the noise reduction effect in Adobe Audition for a quick example, but most other programs will follow a similar process. First highlight a section of your file that contains the specific noise you want to remove. Open the noise reduction filter and click Capture Profile. Hit the Preview button and begin to move the Noise Reduction Level slider as you listen to the playback. Once you find the balance between noise reduction and adverse impact on your main signal, choose Select Entire File and click OK. Now you're ready to add compression.

Caption: Noise and Compression (click to enlarge)

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