“WTF are Loudness Units?” you may ask. Well, they are simply a measure of loudness, just like decibels.
One LU actually is equivalent to one dB. However, an important difference is that Loudness Units are “shaped” according to the human ear’s proclivity to hear certain frequencies more easily than others. Effectively, LUs tend to feel more consistent to our brains than dB will when measuring varying frequency content, and therefore LU meters are preferable to use (compared to, say, RMS meters) for assessing the overall loudness of music.

Below are shown six free LU (aka Loudness Unit) meters, listing features of each. The most important value when matching the loudness of songs is IL (Integrated Loudness), which is the average loudness over the entire course of given time (with very quiet material gated out).

These devices are available as VST effect plugins for any capable VST host (such as Ableton Live, for example).

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HOFA 4U Meter, Fader & MS-Pan
In addition to showing you LU readings, this one also acts as a really nice all-purpose utility for general stereo and level adjustments on any audio track. Its “wider than stereo” panning knobs are super cool!

Stuff It Shows Us
•IL (Integrated Loudness).
•L-R Peak or L-R ISP (True Peak).
•LRA (Loudness Range).

Nifty Functions
•Gain controls for Left & Right (or Mid & Side) channels, and for the combined output.
•360 degree Left & Right channel panning controls!
•Left and right channel phase inversion buttons.

_______find HOFA 4U Meter, Fader & MS-Pan here.

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Youlean Loudness Meter
The thing I like a lot about this one is the “loudness over time” display (aka histogram), which allows you to easily visualize which sections of time are louder than others, and by how much. It’s up to 5.1 channels and also has some presets for various media targets, though not as many as the TB plugins do. It has both a free and a paid version. I went ahead and got the paid version after using the free one for a couple of years.

Stuff It Shows Us
•SL (Short-Term Loudness).
•IL (Integrated Loudness).
•LRA (Loudness Range).
•Momentary Loudness Max.
•Short-Term Loudness Max.
•ISP (True Peak Max).

_______find Youlean Loudness Meter here.

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MLoudnessAnalyzer
I like how you can customize the display of this one to show you exactly what you want, and nothing else. I use it during audio finalization to precisely monitor loudness as well as L-R peak levels for final output.

Stuff It Shows Us
•L-R Peak.
•L-R ISP (True Peak).
•ML Momentary Loudness.
•SL (Short-Term Loudness).
•Short Term Loudness Max.
•IL (Integrated Loudness).
•LRA (Loudness Range).
•PLR (Peak-to-Loudness Ratio).
•Crest.

_______find MLoudnessAnalyzer here.

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TB EBU Loudness
This one has tons of presets for various loudness targets for worldwide media delivery. That and its surround sound channel capability might make it a respectable choice for someone working on audio for film.

Stuff It Shows Us
•IL (Integrated Loudness).
•IL Gate State.
•LRA (Loudness Range).
•ISP (True Peak).
•PLR (Peak-to-Loudness Ratio).
•Integration Time (free, or synced to playback).
•VU, VU+Peak Hold, or SL (Short Term Loudness) 30 seconds to 60 minutes.
_______find TB EBU Loudness here (scroll down to unfold the legacy v3 plugins link).

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dpMeter5
This one is a bit customizable. It’s made by ToneBoosters and like TB EBU Loudness can run up to 5.1 channels and has various target presets, but with more types of readings, such as RMS and Dialog.

Stuff It Shows Us
•IL (Integrated Loudness).
•SL (Short-Term Loudness).
•Short-Term Loudness Max.
•ML (Momentary Loudness).
•Momentary Loudness Max.
•ISP (True Peak Max).
•LRA (Loudness Range).
•ISP (True Peak).
•RMS Integrated.
•RMS Momentary.
•RMS Momentary Max.
•Peak Max.
•Crest.
•ILD (Integrated Loudness Dialog).
•LRA (Loudness Range Dialog).
•Dialog Percentage.

_______find dpMeter here.

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Audiocation AC-R128
This one is pretty darn basic and straightforward.

Stuff It Shows Us
•IL (Integrated Loudness).
•SL (Short-Term Loudness).
•ML (Momentary Loudness).
•Momentary Loudness Max.
•Integration Time.

_______find Audiocation AC-R128 here.

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Two *not free* plugins that I own which show LU readings are the HOFA IQ Analyzer (probably the one plugin I use more than any other, for its before-after spectral energy analysis capability) and the SPL Hawkeye (which I don’t actually use very much).

That’s all for today. Peace!