What is an audio expander?

An audio expander is a thing that changes sound. It makes quiet sounds more quiet. And it lets loud sounds stay loud. This makes a bigger difference between the quiet and loud parts.

Audio expanders are used when making music or other recordings. They give the sound more “oomph”. The loud parts really jump out. And the quiet parts fade into the background.

How does an expander work?

An expander waits for the sound to get below a certain level. This level is called the “threshold”. When the sound goes below the threshold, the expander turns down the volume. It makes those quiet parts even more quiet.

The amount the expander turns down the volume is called the “ratio”. A higher ratio means it will make the quiet parts a lot more quiet compared to the loud parts. A lower ratio means a smaller change between the loud and quiet.

The expander lets the loud sounds pass through without changing them much. So the louder parts keep their original volume. Only the quiet parts get squashed down.

When to use an expander

Music producers and audio engineers use expanders a lot. Expanders can be very helpful in many situations.

Increasing dynamic range

One main reason to use an expander is to increase dynamic range. Dynamic range is the difference in volume between the loudest and softest parts of a recording. More dynamic range makes the music more exciting and emotional to listen to. The song feels like it has more energy.

With an expander, you can make the quiet parts of a song really fade into the background. Then when a loud part hits, it’s much more impactful. The song jumps out with more power and punch.

Reducing noise

Expanders are also good for reducing background noise in a recording. Maybe there’s a low hum or hiss you can hear in the quiet parts. An expander can help get rid of that.

You set the expander threshold just above the level of the noise. Then when the audio signal drops down to the noise, the expander makes it quieter. This can really clean up a recording. The noise fades away and you’re left with just the good stuff.

Tightening up instruments

Another use for expanders is tightening up the sound of certain instruments. This works well for instruments with a very percussive, choppy sound. Guitars and drums are good examples.

The expander turns down the volume whenever the instrument isn’t playing a note. This gets rid of the little sounds between notes, like the buzz of guitar strings or the ring of a drum. The end result is a tighter, punchier sound. All the notes sound more distinct and separate.

Setting up an expander

To use an expander, you’ve got to set it up right. The two most important settings are threshold and ratio. Getting these dialed in makes a big difference.

Setting the threshold

The threshold setting on an expander is very important. It determines when the expander kicks in and starts turning down the volume.

You want to set the threshold just above the level of the unwanted quiet sounds. If it’s too low, the expander will cut off the ends of notes or words, making things sound unnatural. If it’s too high, the expander won’t do much at all.

It’s good to watch the expander’s gain reduction meter while adjusting the threshold. This shows how much the expander is turning down the volume. You can use this to make sure it’s expanding the right amount.

Choosing the right ratio

The ratio is the other key setting. It controls how much the expander turns down the volume when the signal drops below the threshold.

A lower ratio like 1.5:1 will make a subtle change. The quiet parts will be a little bit quieter, but not dramatically so.

Higher ratios like 4:1 create a bigger difference between loud and quiet. The quiet parts will be much quieter than the loud parts. This can sound very dramatic and powerful.

For most situations, a medium ratio around 2:1 or 3:1 works well. It’s enough to make the dynamics pop out, but not so extreme that it sounds weird. With drums or percussion, higher ratios can make things punchier.

Attack and release

There are a couple other expander settings called attack and release. These control how quickly the expander turns down the volume when the signal drops below the threshold, and how fast it turns it back up again when the signal goes above.

Usually you want a fairly fast attack time, so the expander kicks in right away. This avoids any delay before it starts working. A medium-fast release time works for most things. You don’t want it so slow that quiet sounds linger unnaturally.

Tips for using expanders

Here are a few tips and tricks to get the most out of an expander:

• Use your ears, not your eyes. It’s tempting to go by what looks good on the meters. But trust what you actually hear. Adjust the settings until the audio sounds right to you.
• Avoid going overboard with the ratio. Really high ratios can sound unnatural and choppy. Use a lighter touch unless you’re really going for an extreme effect.
• Expanders work best on individual tracks, not the whole mix. Putting an expander on every track can make things sound thin and lifeless. Use them sparingly where they’re most needed.
• To reduce rumble and pops on a vocal track, set a fast attack time to clamp down on those sounds right away. You don’t want them jumbled up with the starts of words or phrases.
• Automating the threshold or ratio over time can create cool effects. You can make the verse of a song really laid back dynamically, then slam into a super punchy chorus.
• Sometimes boosting the signal going into the expander can help get more out of it. This pushes more of the audio above the threshold so it doesn’t get squashed as much. Just watch out for clipping.

Expanders vs. compressors and gates

Expanders are often confused with two other tools: compressors and noise gates. While they’re all dynamics processors that alter the volume of audio over time, they each work in different ways.

Compressors do the opposite of expanders. They turn down the volume of the loudest parts to make the dynamic range smaller. The goal is often to make the overall signal louder and more consistent.

Noise gates are like extreme expanders. When the signal drops below the gate’s threshold, it turns the volume down completely rather than just partway. This creates total silence rather than just making things a bit quieter.

Compressors and gates are more common tools than expanders overall. But expanders have their place for increasing dynamic range, reducing noise, and shaping the envelope of instruments.