An amazing sound from an all-original analog design
When SPL released the IRON mastering compressor, it became an instant icon. Their goal was to create a compressor that provided a pleasant, melodic-sounding, transparent compression, inspired by the vintage compressors of the radio era. But, they wanted it to be versatile enough to adapt perfectly to the needs of modern mastering studios. The resulting 25 lb, 4RU tube compressor was an immediate hit in top mastering studios around the world.

Inspired by tube classics, packed full of 21st century innovations
The IRON set a new benchmark by taking the sonic virtues of legendary vintage tube compressors and adding on modern innovations, including a parallel dual tube circuit, rectifier mode switching, flexible attack and release settings, and a High Dynamic 120V operating voltage.

Like two tube compressors in one
Unlike traditional Vari-Mu designs, which use a single tube for compression, IRON employs a unique dual circuit topology. A specially designed Mu-Metal iron transformer splits the signal between two distinctly different tubes—a 12AX7/ECC83 and a 12AU7/ECC82—each with a slightly different compression curve and feel. These two separate tube compression circuits are run in parallel, and then recombined to taste for a uniquely flexible approach to tube compression.

Far more control than any vintage Vari-Mu compressor
The IRON includes sidechain filters, and Attack and Release parameters that have six different settings ranging from Slow to Fast. These times vary according to the Rectifier circuit selected. Each of the six different Rectifier settings make use of different diode combinations—Germanium, Silicon, LED, and mixed for even more tonal variation. This added control means that mastering is not the only domain where the IRON sets new standards. It can also be used to process subgroups or individual signals, like vocals, bass, guitar, strings and more.

True analog modeling with the power of TMT
The SPL Iron is a TMT plugin, based on the patented Tolerance Modeling Technology by Brainworx. TMT gives you the most realistic analog sound in the box by offering multiple plugin channels with realistic analog tolerances in the components of the circuit modeling. Additional digital-only features include a monomaker, stereo width control, MS processing and more, making the plugin even more powerful than the original.


  • Variable Bias Tube Compressor
  • Parallel Dual Tube Circuit combines two tube types
  • Custom Mu-Metal Iron Transformers
  • Feed-forward resistive Vactrol-Opto-Isolator
  • Six different Rectifier settings available
  • Sidechain that allows you to choose between Off, four sidechain-filter presets or an external sidechain signal
  • In Link mode, the Threshold, Tube Bias, Attack, Release, and Rectifier parameters, as well as the Sidechain EQs, are controlled with the right side (channel 2) of the unit
  • Master out features an additional, Passive Equalizer with two fixed sounds
  • TMT — Brainworx patent-registered “Tolerance Modeling Technology” (US Patent No. 10,725,727)
  • Brainworx plugin only features such as TMT (US Patent No. 10,725,727), M/S Processing, Mono-Maker and Stereo Width, Parallel Mix and Headroom

Audio Examples

Industry Reviews

  • Gentry Studer

    Gentry Studer

    I downloaded the plug in, I've had to shoot it out against the real thing on every project, just to see how it stacks up. You guys did an amazing job with the plug in. Everything from the color it… Read More

  • Michael Romanowski

    Michael Romanowski

    Grammy Award-winning engineer (Alicia Keys, G-Love, Lady Gaga)

    I use the hardware SPL Iron for my mastering everyday. What I love about it is the tonal and dynamic flexibility is has for every style of music. And it’s always smooth and musical. Brainworx… Read More

  • Brendan Duffey

    Brendan Duffey

    When I need a tool that gives me a plethora of gain, tone and shape controls the Iron Mastering Compressor is the first thing I turn to. The Iron Plugin has all the controls features of the… Read More

Customer Reviews

  • Analog 3D sound

    by MiamiDude
    Great for that analog sound, with depth and 3D sound! Great comp!
  • Fernando

    Nice !

    by DJ A-O.N.E.
    Modern sounding vari-mu style compressor. Dances on the master bus and adds its own color and flavor. I was a little skeptical at first but, the once I started to dig into the sound of this beauty,… Read More
  • better than his inspiration

    by Synthitize
    Some give it inspiration from the Fairchild 670;
    But it is better because in addition to colorizing the sound like the 670, from a pure compression point of view, it is much better and it… Read More
  • Endless possibilities when it comes to smooth and transparent compression.

    by Joost
    I just love this on vocals and the mixbus. It has a steep learning curve since it really isn't the most intuitive having all those difference A/R times by switching around the recitifers (could… Read More


Supported Plugin Formats
AAX DSP, AAX Native, AU, AAX AudioSuite, VST2, VST3

Supported Operating Systems
macOS 14 down to macOS 11
Windows 11 down to Windows 10

Intel, or Apple Silicon

x64-compatible CPU

System Requirements
Display resolution: 1440 × 900px or 1280 × 960px or higher
Memory: 2 GB RAM


With the Installation Manager you can select, download & install all the Plugin Alliance products. Select any and all formats you need for your system! Mac & PC.



SPL IRON - Changelog

Version 1.6.1 (Oct 9, 2023)
- General: fixed CPU spikes on Mac OS

Version 1.6.0 (Aug 15, 2023)
- General: added native Apple Silicon compatibility for AAX
- General: added macOS Ventura support
- General: improved plugin loading time in the DAW
- General: fixed issue causing Logic to crash when closing the plugin UI
- General: improved font drawing behavior

Version 1.5 (Mar 15, 2022)
- General: added native Apple Silicon compatibility for VST3, VST2 and AU
- General: added macOS Monterey support
- General: added Windows 11 and Windows 10 21H1 support
- General: discontinued Windows 7 support
- General: discontinued macOS 10.9 and 10.11 support
- General: fixed metering behavior in block sizes of 2048 samples and higher

Version 1.4 (Mar 22, 2021)
- General: Compatibility with Logic on Apple Silicon devices via the Rosetta-2 layer
- General: Fixed possible artefacts when freezing or bouncing tracks in Pro Tools
- General: Fixed automation highlighting disappearing in Studio One
- General: Improved license dialog visibility in dark mode

Version 1.3 (May 27, 2020)
- General: Qualified for use with the Windows 10 May 2020 Update
- General: VST3: Fixed potential hangs in a DAW upon loading
- General: Fixed logical issues in undo / redo behavior
- General: Fixed UI resizing issues in Ableton Live on Windows
- General: Fixed audio processing initialization issues on amp and delay products
- Added scalable UI feature

Version 1.2 (Nov 06, 2019)
- General: Qualified for use with macOS 10.15 Catalina
- General: Qualified for use with Windows 10 November 2019 Update
- General: Fixed plugin validation in Logic under macOS Catalina
- General: Fixed preset name restore in Logic when reopening a session
- General: Fixed opening authorization dialog triggering automation
- General: Improved instantiation times for plugins
- General: Improved license functionality and branding for subscription
- General: Removed 32-bit support on macOS and Windows
- Fixed automation highlighting for the lower area in the mono version

Version 1.1 (Jul 10, 2019)
- General: macOS 10.14.5 Update compatibility
- General: Windows 10 1903 Update compatibility
- General: Fixed activation issue in Windows hosts set to non-English language (e.g. Cakewalk)
- General: AU: Fixed issue with increased CPU and memory on reopening UI
- General: VST3: Fixed issue with adapting to host knob mode, and now prioritizing linear
- General: VST3: Fixed issue with VST3 preset permissions
- General: VST3: Improved synchronization between parameter states and some UI functions, e.g. toolbar reset
- Fixed artifact when switching between LR and MS modes
- Fixed GR meter not being shown in Pro Tools
- Fixed UI coloring not being saved with session

Version 1.0 (Jan 9, 2019)
- Initial Release