Ghost Note Audio has released Spectrum Thief, a free EQ-matching plugin for Windows and macOS.
If the name Ghost Note Audio sounds unfamiliar, don’t start doubting your knowledge of current VST plugin developers. This is the first time I’m checking out their plugins, too.
However, it was interesting to see that they are now hosting the Cloud Seed reverb plugin, which originally began as a free offering. Spectrum Thief is their most recent freeware release, and it’s a convenient tool for tone matching and impulse response capture.
The plugin’s primary function is EQ matching. You capture two frequency responses—one from your source audio and one from a reference—and Spectrum Thief generates a filter to match the source to the target.
The plugin offers controls for smoothing, low and high-end roll-offs, and overall filter strength, giving you the flexibility to dial in subtle or dramatic tone shifts.
What makes it even more interesting is the ability to export the generated filter as an impulse response. This opens up all sorts of possibilities, from quickly capturing the sonic character of a guitar cabinet to creating mix-wide tone-matching adjustments.
For guitarists, it’s a fast and effective way to clone a favorite cab sound or create a makeshift “cab IR” using a mic and amp setup.
I gave it a quick test with a couple of guitar tracks and was impressed with how well the tone-matching worked. You can swap the source and target spectra with a click, which makes A/B comparisons super easy. You also get real-time auditioning, and the plugin does a good job of maintaining clarity even with heavier filtering applied.
There’s also a Live FFT mode for real-time visual feedback, and you can view or truncate the impulse response before exporting it. Exported IRs can be saved as WAV files and used in other plugins or hardware units.
You don’t need to register or activate anything, and that alone makes it worth grabbing. It’s one of the most user-friendly and capable free IR tools I’ve seen.
Spectrum Thief is available in VST format for Windows and macOS, and as an AU plugin for macOS users. It supports AVX-equipped CPUs on PC (Intel/AMD post-2013), and both Intel and Apple Silicon Macs running macOS 10.15 or later.
You can download it for free from the Ghost Note Audio website.
Download: Spectrum Thief
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Last Updated on July 16, 2025 by Tomislav Zlatic.
