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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