Layer 6.jpg

The All-Elusive ‘Expander’

What exactly is an expander on a channel strip or within a gate?

Most of us in the field of audio and its many facets, whether it be as a professional or amateur, have experience using a noise-gate. Where there is a noise-gate, there is usually an “Expander.” What even is an Expander? Obviously, it is a process that “expands” . . . but I plan to dig in deeper in order to shed some light on expanders and moreover, the practical application of using them in our workflow.

There are a few important distinctions to make when conceptually separating an expander from other dynamic processes, such as a compressor or gate. All of these have very similar controls such as a ratio, threshold, attack & release, but expanders usually also contain a “Range” control.

The most simple explanation of an expander is that it increases the dynamic range of the audio that's running through it. This sounds amazing, doesn't it?! Behaving oppositely from a compressor, there may come a time when it is just the tool needed . . . or so it may seem.

There are two types of expanders, upward & downward. Downward refers to making a quiet sound even quieter, while an upward-type of expansion refers to making a loud sound even louder. How this happens and to what extent depends on the expander's threshold and range. When the audio level is above that of the threshold, upward expansion occurs; when the audio signal is below the threshold, downward expansion will occur.

To be more precise, here are the parameters of an expander:

Attack: Sets how fast expansion responds when a signal level crosses the threshold

Release: Sets how fast the expansion recovers after a signal level crosses the threshold

Threshold: Sets the level where expansion occurs

Ratio: Sets the amount of expansion that is applied

Range: Limits the maximum amount of applied gain change

Honestly, I have not used expanders very often, but as a result of my research it appears the following are the best descriptions and uses for an expander, both upward and downward. Shout out to Fabfilter to their amazing plug-ins! Below features their multiband compressor for examples.

Layer 6.jpg

Upward Expansion

With upward expansion, it appears it could be a useful tool to help bring out attack and excitement on particular sound sources that are already usually very dynamic. This includes drums and piano or even vocals. I have read about expanders being used in mixing to aid in making a vocal more prominent by adding a sort of transient shaping.

Layer 7.jpg

Downward Expansion

Downward expansion appears to be the most common type of expansion and is most similar to that of a noise-gate. By attenuating the signal when it falls below the set threshold, more dynamic range will theoretically be achieved. Mastering engineers may sometimes utilize this tool in the instance of receiving a ‘ready-for-master’ mix that is over-compressed. Downward expanders also seem to have some viability in the realm of reducing noise and bleed in a mix; it can be used as a less-aggressive gate. Others have described using expanders to help control reverb tails, delays and echos.

Involving the use of expanders in ones’ mixing workflow sounds great . . . however, armed with the knowledge of what expanders are and how they may be used, I find myself wondering what the practical applications of using them are and how helpful they may be in real-world scenarios. For help on this mission, I have turned to friend, colleague and Grammy-Award Winning Engineer: Clark Hagan. If there is anyone with experience on the practical application of various audio processes, it is him.

My questions posed to Mr. Hagan were simple and straightforward; what is an expander to you and how often have you used it in your career. It turns out that Clark, “. . . rarely used expanders . . .”

When asked about the practicality of expanders, Clark provided more insight on when he personally has used them, “I think sometimes expanders are a tool for when you want to correct something that wasn’t recorded correctly . . . but there are also great tricks expanders can be used for..”

As with any type of audio processing, one must simply take the time to experiment with them to find how it may be useful in his or her workflow. Personally, after much research and many conversations concerning expanders, I most definitely plan on at least attempting to add it as just one more tool in my ever-expanding ‘audio tool bag’ and will follow up with all of you on my successes and failures in the next edition of KMGLife® Inc.’s Blog!