UnderTone Audio UnFairchild 1.0.8 Mac

The UnderTone Audio UnFairchild plugin runs on any Mac with macOS 10.13 or later and an ARM or 64-bit x86 processor.

UnderTone Audio built the unit in collaboration with MIXLAND and producer Eric Valentine. Here is what ships in version 1.0.8.

Vari‑mu compression — a tube-emulation dynamics processor modelled on a vintage hardware design.

THD control — an overall total harmonic distortion circuit that lets the user dial in analogue‑style saturation.

DC Threshold — a user‑adjustable control that shifts the compressor’s knee point.

Feed‑Back / Feed‑Forward — two detection paths that change how the side‑chain senses the input signal.

Time constants — six original preset release shapes plus four variable settings.

MS function — mid‑side processing for independent control of the stereo centre and the side signal.

Wet/dry control — built‑in parallel compression without extra routing.

Side chain processing and output level control are also included. UnderTone Audio lists drums as a suitable source for the compressor, though the plugin works across full program material. The interface is in English.

Metering refresh fixed on Apple Silicon

The 1.0.8 build settled a handful of edge-case behaviours that users had flagged in earlier releases. Metering on Apple Silicon machines now refreshes without the occasional frame skip that appeared when the GUI was open alongside several other plug-in windows. The DC Threshold knob responds more predictably at extreme settings — previously, values past 80% could cause the gain reduction needle to jump rather than glide. For anyone running the unfairchild plugin inside a DAW that sandboxes its plug-ins, the recall of the four variable time constants is now sample-accurate across sessions.

One change that matters in a busy mix session: true bypass engages and disengages with no audible click, even when the compressor is under heavy gain reduction. Earlier builds sometimes produced a tiny transient when switching bypass at high input levels. That is gone as of 1.0.8. The left/right balance fine-adjustment also holds its calibration better after a project reload — a detail that mastering engineers working with asymmetrical stereo material will notice immediately.

AU and VST3 support across major DAWs

UnderTone Audio ships the UnFairchild as a standard VST3 and AU plug-in, so it drops into Logic Pro, Ableton Live, Cubase, and REAPER without a wrapper. On a Mac running macOS 10.13 or later, the plug-in works alongside any other AU or VST3 effect. Because the THD circuit generates harmonics that change with the input level, the order of processing matters. Placing the UnFairchild after a clean digital EQ lets the saturation react to the EQ curve; placing it before a surgical compressor on a drum bus lets the THD act as a subtle glue before the second gain stage clamps the transients.

The MS function ties directly into macOS's multi-channel audio handling. When a stereo track is routed through the plug-in, the mid and side channels appear as separate processing paths inside the plug-in — no extra routing in the DAW needed. The side chain input follows the host application's side-chain bus assignment, which on macOS uses the standard AU side-chain spec. That means the plug-in listens to any mono or stereo send without fuss, whether the key signal comes from a kick drum mic or a dialogue stem in a post-production session.

The wet/dry control is a single knob, so parallel compression happens inside the plug-in rather than across two mixer channels. That saves CPU overhead on Apple Silicon machines, where the plug-in runs natively and leaves the efficiency cores free for other tasks. Users who run large mix templates will find the UnFairchild sits comfortably on a dozen drum tracks without pushing the system into overload.

Compared with similar vari-mu plug-ins

Three vari-mu compressors show up in the same conversations as the Undertone audio release. The first is the Pulsar Mu, which models a classic British console compressor. The Pulsar offers a softer knee and a darker saturation character. Its time constants are fixed to the original hardware values — no variable settings, no DC Threshold adjustment. The UnFairchild gives more control over the compression shape itself, which suits mix engineers who need to tune the response to a specific source rather than working within a single hardware template.

The second is the Arturia Comp Tube-STA, an emulation of an American tube leveling amplifier. The Arturia plug-in is lighter on CPU and simpler in layout, with only a couple of time constants and no mid-side processing. Its saturation is warmer and more obvious at low gain-reduction settings. The UnFairchild runs cleaner in the bottom octave and provides the feed-forward path that the Arturia lacks — a difference that becomes clear on bass-heavy material where the engineer wants the compressor to catch peaks without thickening the sub frequencies.

The third is the Klanghelm MJUC, a variable-mu design with three distinct circuit models inside one plug-in. The MJUC covers more ground in terms of tone, but none of its circuits replicates the UnFairchild 670M mkII hardware. The MJUC lacks a THD control separate from the compression circuit, and its mid-side mode is limited to one of the three models. The UnFairchild focuses on one circuit and exposes every parameter that the hardware offers, from DC Threshold to left/right balance fine-adjustment. For someone specifically after the sound of the Undertone Audio hardware — the same circuit that Eric Valentine helped tune — the plugin is a narrower but deeper tool.

• macOS 10.13 or later
• ARM or 64-bit x86 processor