Tag Archives: Expansion

A Homebrew Upward Expander

You can make an upward expander with two signal lines, a gate, and a summing bus.

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On Twitter, I was having a conversation with @GibsonGirl5775 about gates and expanders. Expanders are the complementary process to compressors – they act to increase dynamic range, whereas compressors reduce dynamic range. A gate is just an “extreme” expander, because it expands signals all the way down to silence.

“Down” being key.

I had begun the conversation by mentioning that the version of Logic that I had (way back when) included an UPWARD expander, and that I kinda missed that plugin. Upward expanders can have a markedly different sound than a gate, because they are very well suited for gentle expansion versus full gating. You set your threshold, attack, and release as normal, but then you also get a “ratio” control. The ratio is similar to what you find with a compressor, except it works in reverse. For every dB that a signal EXCEEDS the threshold, some specified amount of gain is ADDED to the signal.

I don’t see a lot of upward expanders out there. Hey, I don’t even see many expanders, period. Full gates are very common. (The software that I use, Reaper, has a gate that you can transform into an expander by simply adding in some “dry” signal.) The nifty thing about expanders is that you don’t completely lose a signal when it drops below the threshold. This means that you can keep certain subtleties of the processed sound – albeit at a lower volume.


The Twitter conversation got me thinking: “If the Reaper gate allows me to make an expander by adding dry signal to the gated signal, can’t there be a way to make an upward expander as well?”

The answer is “yes, pretty much.”

It turns out that, with a bit of signal routing and a bog-standard gate, pretty much anybody can “hack” an upward expander together. The result isn’t exactly the same as a true upward expander, because the gain addition is a fixed amount and not directly ratio driven. Still, the similarity is fairly close.

Essentially, what we’re doing is parallel gating, as opposed to parallel or “New York” compression.

The cool thing is that this trick can work everywhere. You can do it on an analog console, or in the digital realm. All you need is a signal, a summing bus, and a way to send that signal down two channels that are connected to that summing bus. An aux send returned into a channel can serve well as a split.

The setup works like this:

  • Your original signal is split into two paths – “dry” and “processed.”
  • You gate the processed path to taste. You also apply post-gate positive gain of some amount.
  • Both signal paths are fed into a bus.

Here’s a diagram:

To give you an example of how this sounds, here’s an unprocessed original signal of kick and snare, followed by a processed version of the same thing. (The “double-hits” you hear at times are kick-beater bounces and snare ghost-notes. The gate output is right on time, I promise.)



Figuring out where upward expansion is more handy than downward expansion is up to you. Like I said before, I kinda miss the option of an honest-to-goodness upward expander. However, I also have to admit that having an upward expander has become mostly just a curiosity. I’ve become plenty comfortable with downward expanders, and so I’m not suffering for lack of toys.

I’ll close by saying that I think there’s a more generalized upshot to all this, which is probably the most important element:

Audio processing is just a bunch of basic operations being strung together – Gain, time, level detection, summation, etc. If you don’t have the exact processing you need in an “already boxed up” fashion, you can often construct something very like what you want. You just have to figure out how the pre-built device puts the pieces together.