What Is Included?

oXygen is arranged like a mastering rack. Each module can be bypassed, collapsed or moved inside the processing chain, allowing producers to work manually or begin with settings suggested by the analysis tools.

• 15-band graphic EQ: Fixed mastering bands extending from 30 Hz to 20 kHz.
• Four-band dynamic EQ: Dynamic cuts for low-end buildup, excessive body, aggressive presence and sharp high frequencies.
• Four-band multiband compressor: Independent control over low, low-mid, high-mid and high-frequency areas.
• Stereo Imager: Multiband Mid/Side width adjustment with low-frequency protection.
• Gain Stage: Dedicated level control before the final loudness processor.
• Maximizer: True-peak-aware limiting with Transparent, Loud and Safe operating modes.
• Master Assistant: Automatic analysis and suggested mastering settings.
• Reference Match: Tonal and dynamic comparison with an external reference track.
• Analyzer: Simultaneous display of the original and processed frequency spectra.

The current signal order is Graphic EQ, Dynamic EQ, Multiband Compressor, Stereo Imager, Gain and Maximizer.

Master Assistant

Master Assistant listens to up to sixty seconds of audio from the master bus. It examines tonal balance, crest factor, dynamics, stereo spread, loudness and reconstructed peak behaviour before preparing a suggested rack configuration.

The latest version includes twenty-six musical profiles covering broader genres and more specific directions such as modern Pop, acoustic Pop, Lo-Fi Hip-Hop, Boom Bap, Trap and Drill, club-oriented electronic music, Ambient, Indie Rock, Hard Rock, cinematic music and several forms of Metal.

The assistant also selects an artistic direction and an appropriate maximizer mode. A denser electronic production may receive different loudness and stereo recommendations from an acoustic solo track or chamber arrangement.

The proposed settings are not applied silently. Users can review and confirm the suggestion before the plugin writes the values into the processing modules.

As with any automatic mastering system, the result should be treated as a starting point. The assistant cannot know the artistic intention behind every mix, especially when the correct decision is to preserve an unusual tonal balance rather than correct it.

Reference Match

Reference Match allows a WAV or FLAC track to be loaded directly into the plugin. oXygen analyses up to sixty seconds of the reference before listening to the incoming mix for the same maximum duration.

The system then proposes changes intended to move the master toward the reference profile. EQ matching receives the strongest priority, followed by dynamic control, resonance reduction, stereo width and loudness.

This workflow is useful when mastering several songs for an EP, creating consistency across an album or comparing a mix with a professionally released track from a similar genre.

The reference should still be selected carefully. A heavily limited festival track is not automatically an appropriate target for an intimate acoustic production. Matching the wrong reference precisely is simply a very efficient way to travel in the wrong direction.

Graphic and Dynamic EQ

The fifteen-band graphic EQ is intended for broad tonal correction and enhancement. Its fixed bands cover the complete audible spectrum, making it suitable for balancing excessive bass, recessed mids, harsh upper frequencies or a master that needs slightly more air.

The four-band dynamic EQ handles problems that appear only during certain musical passages. It can reduce low-mid buildup when several instruments play together, control upper-mid aggression during a loud chorus or smooth an overly bright high-frequency section without applying a permanent static cut.

Dynamic processing is particularly useful during mastering because a constant EQ reduction can affect sections that were already balanced correctly.

Use small moves and compare the original and processed curves in the analyzer. The visual display is useful for confirming changes, but it should not replace listening on monitors, headphones and smaller playback systems.

Multiband Compression and Stereo Imaging

The multiband compressor divides the signal into low, low-mid, high-mid and high-frequency regions using phase-matched Linkwitz-Riley crossovers.

Each section uses stereo-linked peak and RMS detection, soft knees and program-dependent release behaviour. This allows oXygen to control an unstable bass region without forcing the high frequencies through the same amount of compression.

The compressor works best with restrained gain reduction. Mastering compression should improve consistency and glue without removing the musical contrast between verses, choruses, breakdowns and drops.

The Stereo Imager uses multiband Mid/Side processing. Upper-frequency bands can be widened while the low end remains more conservative for improved mono compatibility.

Correlation protection and energy compensation help prevent extreme width settings from weakening the central image. Even so, important elements such as kick, sub-bass, lead vocals and snare should remain stable when the master is checked in mono.

Maximizer and Final Loudness

The Maximizer is the final loudness stage. It uses four-times reconstructed peak detection, lookahead limiting, adaptive release and host latency reporting.

Three modes are available:

• Transparent: The most neutral starting point for preserving punch and transient detail.
• Loud: A denser mode for modern electronic, Pop, Hip-Hop and other loudness-focused productions.
• Safe: A more conservative option for mixes that are already loud, bright or transient-heavy.

The maximizer should not be expected to repair uncontrolled peaks created earlier in the mix. If the limiter needs extreme gain reduction, return to the kick, snare, bass or other dominant elements and correct them before the mastering stage.

Use an external LUFS and true-peak meter after oXygen when preparing the final delivery file. Loudness targets depend on the musical style and intended destination, and streaming normalization should not be treated as a compulsory mastering target.

How to Use oXygen

Insert oXygen on the stereo master bus after the mix has been completed. Leave enough headroom and make sure the incoming signal is not already clipping.

Play the loudest or most information-rich section when using Master Assistant. A quiet introduction may not contain enough bass, percussion or vocal information to represent the complete production accurately.

After the analysis, confirm the proposed settings and compare the processed result with the original at a similar perceived loudness.

Use the analyzer to identify broad tonal changes, then adjust the EQ, dynamic EQ and compressor manually. Treat the automatic settings as an informed suggestion rather than a final command from the mastering authorities.

Check the stereo image in mono, refine the gain entering the Maximizer and select the mode that preserves the best balance between loudness, clarity and punch.

Compatibility and Installation

oXygen is available as a VST3 plugin for Windows, macOS and Linux.

• Windows: 64-bit VST3 build
• macOS: VST3, requiring macOS Monterey 12 or later
• Linux: VST3 build for compatible 64-bit distributions
• Bus formats: Mono and stereo
• Signal precision: Native single and double-precision DSP paths
• Current version: 1.0.4
• Licence: BSD 3-Clause open-source licence
• Price: Completely free

The developer notes that Windows packaging and broader host validation are still evolving. As with any young open-source plugin, test it in a copy of the project before placing it permanently inside an important mastering session.

Final Verdict

oXygen is an ambitious free mastering suite that brings together most of the essential final-processing stages inside one coherent rack.

The combination of graphic EQ, dynamic EQ, multiband compression, stereo imaging and true-peak-aware limiting makes it useful even without the automatic functions. Master Assistant and Reference Match add faster starting points for producers who are still learning how each mastering decision affects the complete mix.

The plugin remains a relatively young open-source project, and users should expect its compatibility and workflow to continue evolving. It should not replace careful mixing, accurate monitoring or critical listening.

For independent producers looking for a complete free mastering VST3 on Windows, macOS or Linux, oXygen offers an unusually broad feature set. It can suggest the settings, match the reference and control the peaks, but it still refuses to accept responsibility for a kick that was six decibels too loud in the mix.

Download oXygen Mastering Suite from the official GitHub page:

Download oXygen Free

https://github.com/Wamphyre/oXygen/releases