Purr-LUFS
by Noisebud · Utility · LUFS gain matcher
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Purr-LUFS is a Noisebud gain-compensation plugin that uses LUFS to keep a processing chain at the same loudness, removing loudness bias from A/B comparisons.
A semi-lock slows the compensation within a threshold, and Reaper routing helpers are included; it is available through Patreon from $5.
Best for: Mix Bus, Mastering. Genres: all genres.
Keywords: metering, auto-gain, mastering, bus processing, mix bus, full mix, A/B compare, utility.
What it does
Purr-LUFS is a LUFS-based gain compensation plugin from Noisebud. It measures the loudness going into a plugin, a hardware insert or a whole effects chain and keeps the output at that loudness, so you can judge processing without the louder version always sounding better. The developer says it removes the "bias toward preferring what's louder".
- LUFS matching: compensates the output of a chain back to the loudness of its input, for fair before/after comparisons.
- Semi-lock: inside a loudness threshold you set, compensation slows down instead of chasing every change, so small level moves from your processing stay audible.
- Auto Semi-Lock: added in version 2, it engages the semi-lock on its own once the processed signal reaches the threshold.
- Threshold and Speed: the threshold defaults to 1 dB and the compensation speed to 3 seconds; both are adjustable.
- Purr-Router: a helper for Reaper that handles the routing of the dry signal to Purr-LUFS. A Purr-Configurator script is also included for complex Reaper routing.
Version 2.01 is a patron download through Noisebud's Patreon. In June 2026 Noisebud announced Purr-LUFS 3, in which Purr-Router sends the dry audio to Purr-LUFS outside the DAW's routing, plus a Sync function and Pre, Delta and Bypass buttons; demos of version 3 are offered.
When to use it
Purr-LUFS is the pick when you want loudness matching to happen automatically around a chain while you tweak it. Unlike Youlean Loudness Meter 2 and LEVELS, it doesn't just measure loudness; it corrects the output level so your ears hear the processing, not the gain change. Compared with Metric AB and REFERENCE 3, which level-match your mix against reference tracks, it matches a chain against its own input, which is a different job. It is also much simpler than those tools, with no metering display or spectrum view to speak of.
- Best for: loudness-matched before/after checks on compressors, saturators, EQs and whole mastering or mix-bus chains, including hardware inserts.
- Genres: any.
- Look elsewhere if: you need full loudness metering for delivery (Youlean Loudness Meter 2, WLM Plus) or A/B comparison against reference tracks (Metric AB, REFERENCE 3).
- Tip: the developer suggests a higher threshold for subtle dynamic processing, and longer speed and tighter threshold settings (down to 0.1 dB) for mastering; the defaults suit most work.
Where to buy
- Noisebud: see store (Available to Noisebud Patreon members, from $5 a month.)
Tutorials and reviews
- Noisebud - Purr LUFS v2.00 - Loudness Compensate any plugin…
- How to set up Purr LUFS or Purr Fect in Reaper
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