SL473 Is A FREE Compressor Plugin By SmackLabs

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SmackLabs offers SL473, a freeware audio compressor VST plugin for Windows.

The SL473 plugin is available for download in 64-bit VST format via the developer’s Buy Me A Coffee page. There are a couple of freebies there, so feel free to buy them a coffee if you like their work.

As you might have guessed based on its interface, the SL473 is based on a VCA design from the 1970s that was prominent in vinyl disc cutting. That compressor is the Neumann 473, a German-designed unit that was a go-to for limiting by the late 1970s.

The thing that made the U473 so interesting was that it offered compressor/limiter/expander functions that you could control independently.

Neumann manufactured the U473 and the U473A. The only difference between the two is that the U473 has a Mono/Stereo switch, where the U473A has a De-ess/Lin switch.

As vintage gear goes, these units are not as expensive as some of the more iconic compressors/limiters. If you can find an original unit in good condition, you could likely pick it up comfortably under £1000.

SmackLabs has gone without the Mono/Stereo and De-ess/Lin switches in what is otherwise a pretty like-for-like GUI.

Like the original hardware, the controls are easily identifiable. Although, both the hardware and software are said to carry a slight learning curve before getting the best out of them.

On the left, you’ll see the Expander controls (yellow) – Recovery and Threshold. There’s also a Bypass switch on the left.

You’ll find the Compressor controls (black) in the middle, with Compr Gain, Recovery, Attack, and Output knobs. The Compressor has a fixed threshold, which means there is no threshold control (the legendary UA 1176 and LA-2A units are also fixed threshold).

Rather than a threshold knob, you use the Compr Gain, and when the signal becomes louder than the threshold, the compressor steps in accordingly. Beyond the Compressor controls is a useful Bass Cut switch.

As I’m not a Windows user (yet), I can’t really say how good this plugin is. What I can say is that the hardware units were amongst the most loved and trusted when it came to gluing a mix together. Whether used on a group, stem, or mix bus, they delivered what is now a vintage sound while remaining reassuringly transparent and musical.

If the SL473 gets close to the original, SmackLabs has done a fantastic job, and we should be happy it’s available for free.

And, if free compressors are your thing, check out the SK-100 from SNFK, a free dual stereo buss compressor that we covered a while back.

Download: SL473 (5.95 MB download size, DLL file, 64-bit VST plugin format for Windows)

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About Author

James is a musician and writer from Scotland. An avid synth fan, sound designer, and coffee drinker. Sometimes found wandering around Europe with an MPC in hand.

1 Comment

  1. I tried it. In tests it sounded and behaved good. Most tests were done on warm loud lo fi… it made louder, and fatter, no untimely dips or volume modulations.. snappy transients.. it brought the floor up in the best way. dont go for more than -6db in reduction

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