Download UnderTone Audio UnFairchild for macOS

If you know the weight a vari-mu circuit brings to a drum bus, the UnFairchild plugin lands with a familiar heft. It's a direct port of the UnFairchild 670M mkII hardware, built with MIXLAND and Eric Valentine to keep the signal path as close to the console original as code allows.

Compatibility is straightforward. It runs on macOS 10.13 and later, native on Apple Silicon and Intel, so no Rosetta juggling in a modern DAW. The feature set reads like a mastering engineer's shortlist. True bypass keeps gain staging honest. A wet/dry knob opens up parallel compression without extra routing. Feed-Back and Feed-Forward modes change the detector path, so you can shift between a smoother grab and a snappier response. The DC Threshold control and fine left/right balance let you shape the stereo field and low-end behaviour with precision, while the MS function decouples the mid and side signals. An output level control rounds out the back end, keeping loudness consistent after heavy gain reduction. It's a tidy, focused tool that doesn't try to be everything—just a specific, musical compressor with a clear lineage.

The first few times you strap it across a mix bus, the wet/dry knob can trip you up. It's easy to dial in a lush, squeezed parallel blend, then realise the dry signal is phasing slightly against the processed path. The fix is simple: engage true bypass and flip the wet/dry balance while listening in mono. On most systems the plugin reports latency correctly, but if your DAW's delay compensation stumbles, nudging the track by a few samples clears it up. Another snag shows up with the DC Threshold when you push it low on a bass-heavy track. The compressor can feel like it's ignoring the kick drum. Raise the threshold a touch and the detector wakes up, grabbing the low end without pumping the whole mix.

The MS mode is powerful but unforgiving. If you squash the side signal hard while leaving the mid open, cymbal tails can smear across the stereo field. A light hand on the side gain reduction—rarely more than two or three dB—keeps width intact without losing control. And when the THD control sits too high on a bright vocal, the top end can turn brittle. Backing it off to around 11 o'clock usually brings back the warmth without the edge.

A quick session with a drum bus

Picture a four-bar rock loop: kick, snare, hats, a touch of room ambience. The raw tracks hit the bus with peaks around minus six. You insert the UnFairchild and start with the Feed-Back mode, the original time constant on setting three. Attack and release are baked into that preset, so you focus on the input gain. Pushing it until the needle kisses four dB of reduction, the snare tightens up without losing its crack. The kick gains a rounded, pillowy thump—classic vari-mu behaviour.

You switch to Feed-Forward to hear the difference. The compression grabs sooner, more assertive. The hats pull back slightly, and the room mic feels a little drier. It's not better or worse, just a different glue. You settle on Feed-Back for this track. Next, you crack the wet/dry knob to about 60 percent wet, blending the compressed signal with the raw transients. The kick punches through again while the body of the kit stays thick. A small nudge on the left/right balance centres the image, then you add a whisper of THD—barely past nine o'clock—and the whole bus feels like it's running through a console summing stage. You print it and move on. Three minutes, start to finish.

No iLok and no always-online activation

Does it need an iLok or online activation? The package includes its own activation method, so you won't be tied to a dongle or a constant internet connection. Install it and it's ready.

Will it run natively on an M1 or M2 Mac? Yes. The plugin is compiled for ARM and 64-bit Intel, so Apple Silicon machines run it without Rosetta. Performance is snappy even on older M1 hardware.

How does it compare to other vari-mu plugins? The UnFairchild is modelled on a specific hardware revision—the 670M mkII—with input from Eric Valentine. It leans into the dirtier, more coloured side of vari-mu compression, especially with the THD control engaged, rather than chasing a clean, transparent squeeze.

Is the unfairchild plugin a standalone app? No, it's a plugin only. You'll need a host that supports VST, AU or AAX formats on macOS 10.13 or later.

Can it do the Fairchild 670 thing on a vocal? Absolutely. The original time constants and the feedback topology give you that same pillowy, levelling compression that sits a vocal in a mix without obvious gain pumping. Crank the input, keep the reduction around five to seven dB, and blend to taste.

Good to know: the DC Threshold is user-adjustable, giving you a direct handle on how the compressor reacts to low-frequency energy.

• macOS 10.13 or later
• Apple Silicon or Intel processor
• VST, AU, or AAX compatible host