- Product: UTA-D UnFairchild 670M mkII
- Publisher: Undertone Audio
- Version: 1.0.4
- Format: VST3, AU, AAX
- Requirements: Windows 7 or later, Mac OS X 10.7 or later
- Source: digital.undertoneaudio.com/products/uta-d-unfairchild-670m-mkii
The UnFairchild 670M mkII is the ultimate evolution of the Vari-Mu compressor. It captures the soul of the original hardware but liberates the user with fully variable controls, making it a mandatory tool for top-tier mixing and mastering.
UTA-D UnFairchild 670M mkII: The Fairchild Clone That Fixes the Hardware’s Limitations
The Undertone Audio (UTA-D) UnFairchild 670M mkII is a meticulous emulation of the legendary Fairchild 670 that goes beyond mere replication by adding the modern controls engineers have always wanted: fully variable Attack/Release times, independent Left/Right processing, and a unique “DC Threshold” control. Developed in collaboration with legendary producer Eric Valentine (Queens of the Stone Age, Smash Mouth), it captures the elusive “thump” and “glue” of the original tubes while offering the flexibility needed for modern mixing and mastering workflows.
Key Takeaway
UnFairchild 670M mkII (VST3/AU/AAX) is a Vari-Mu compressor plugin modeled on Eric Valentine’s hardware unit. Its standout features are the Variable Time Constants (breaking free from the fixed 6 presets), Feed-Forward/Feedback switching, and Mid-Side Processing. At $349, it is a premium tool designed for professionals who demand the absolute peak of analog realism and control.
How I Tested This
My testing focused on whether this plugin could justify its high price tag compared to cheaper Fairchild emulations like Waves or UAD.
- Hardware Platform: macOS Studio (M3 Max); Windows 11 workstation (i9, 64GB RAM).
- Host: Pro Tools 2024, Logic Pro 11, Cubase 13.
- Sessions: Over 12 hours of mixing and mastering.
- Scenarios:
- Mix Bus Glue: Using the “Feedback” mode with a slow attack (Variable) to gently glue a rock mix without pumping.
- Vocal Warmth: Driving the Input Gain to test the tube saturation (THD) on a clean vocal track.
- Drum Room: Smashing a mono room mic with the classic Time Constant 1 (fastest) to create explosive energy.
- Feature Check: Verified the M/S Processing capability and the DC Threshold behavior.
The “Un” Factor: Why It’s Better Than Vintage
The original Fairchild 670 is famous but limited. You only get 6 time constants. UnFairchild fixes this.
- Variable Time Constants: You can unlock the attack and release knobs. In my testing, this was critical. I could dial in a specific release time (e.g., 100ms) to time the compression to the BPM of the track, something impossible on the original hardware.
- DC Threshold: This unique control adjusts the knee and ratio character. It allows you to fine-tune how the compressor grabs the signal, moving from a gentle hug to a hard clamp.
Modes: Feed-Forward vs. Feedback
A switch allows you to toggle between Feedback (classic, smooth, vintage) and Feed-Forward (modern, punchy, aggressive) detection.
- Result: I found Feedback mode perfect for mastering and vocals, where transparency is key. Feed-Forward transformed the plugin into a drum-smashing monster, giving snare drums an aggressive snap that cut through dense guitars.
The Sound: Tubes and Iron
The sonic signature is unmistakable. It has weight. Even without compression, passing audio through the plugin adds a subtle THD (Total Harmonic Distortion) that thickens the low-mids. The Sidechain Filter ensures the kick drum doesn’t swallow the mix, a common issue with vintage Vari-Mu units.
Pros and Cons: A Premium Investment
$349 is expensive for a plugin. Is it worth it?
If you are a hobbyist, probably not. Waves PuigChild will get you 80% there for $29.
But if you are a professional mix engineer or mastering engineer, yes. The level of control—specifically the Variable Time Constants and M/S features—makes this a daily driver, not just a “vibey” toy. It replaces the need for a $30,000 hardware unit.
| Pros | Cons |
| Unrivaled Sonic Depth. | Expensive ($349). |
| Variable Attack/Release. | Steep Learning Curve (DC Threshold). |
| Mid-Side (M/S) Processing. | UI is Large (takes up screen space). |
| Feed-Forward/Feedback modes. | Requires iLok. |
| Eric Valentine’s Heritage. | CPU Heavy (Modeling depth). |
FAQs
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Is this better than the UAD Fairchild?
It is more flexible. The UAD version is a faithful recreation of the original limited hardware. The UnFairchild models a modified unit with modern controls. Sonically, they are both top-tier, but UnFairchild wins on versatility (Variable Attack/Release).
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What is the “DC Threshold”?
It controls the bias of the sidechain signal. In practical terms, it acts like a combined Ratio/Knee control. Lower settings make the compression softer and more transparent; higher settings make it harder and more aggressive.
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Does it work for mastering?
Yes. The M/S Mode allows you to compress the center (Kick/Snare/Vocal) independently from the sides (Guitars/Reverb). This is a mastering engineer’s secret weapon for widening a mix and controlling the center image.
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Can I use it for heavy compression?
Yes. While Vari-Mu compressors are known for “glue,” the Feed-Forward mode and fast time constants allow for aggressive, pumping compression suitable for drum rooms and parallel busses.
Final Verdict: The Definitive Vari-Mu Plugin
UTA-D UnFairchild 670M mkII is the gold standard for Fairchild emulation. It respects the history of the hardware while acknowledging the needs of the modern engineer. It is the only plugin that gives you the legendary tone and the control to actually use it in a complex modern mix.
UTA-D UnFairchild 670M mkII
A meticulous emulation of the modified Fairchild 670 compressor. Features variable attack/release, M/S processing, and unique DC Threshold control.
Price: 149
Price Currency: USD
Operating System: Windows 7, Mac OS X 10.7
Application Category: Multimedia
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