APU Software

APU Loudness Compressor

LUFS, True Peak, RMS, Peak

The APU Loudness Compressor is a real-time compressor / expander designed to support modern loudness types (LUFS, True Peak). Since LUFS is a more accurate measure of loudness, the result is very transparent compression, making it particularly well suited for mastering and post-production workflows.

The compressor is also capable of operating in a more traditional way, using RMS or Peak units of measurement, so you can have your cake and eat it too.

One of the other features of this compressor is the addition of a “Source → Target” mode. In this mode, all loudness measurements inside the source range are compressed or expanded into the target range. In this mode, you don’t need to worry as much about whether you’re compressing or expanding, you just need to set the source and target ranges to your liking. Compression and expansion are both handled automatically.



System requirements: macOS 10.14 (x86, x64, ARM), Windows 10 (x86, x64), OpenGL 3.2.
Supported software formats: Standalone application, VST, AU, AAX (Pro Tools 11+).

Loudness flavors

One of the key features of this compressor is its support for a variety of loudness types. The compressor’s detection circuitry can be configured to use either LUFS or traditional measurement units (RMS, Peak). You can also choose to split or link channels, which is particularly useful for multi-channel audio formats such as Dolby Atmos®.

The compressor’s detection circuitry can be configured to use any of the following loudness types:

Momentary

Momentary is a short duration LUFS measurement (400ms), which is useful for processing the audio’s moment-by-moment dynamics. This mode is responsive but also transparent, making it an appropriate default for the compressor. K-weighting and channel weighting are applied to the compressor’s detection circuitry, improving perceptual accuracy.

Momentary LUFS

Short-Term

Short-Term is a longer duration LUFS measurement (3 seconds), which is useful for processing the audio’s large scale dynamics. Given the longer duration, this mode is less responsive than momentary, but it can be useful for adjusting the bigger picture of the audio’s dynamics. K-weighting and channel weighting are applied as with momentary.

Short-Term LUFS

RMS

RMS loudness types use a rolling time interval of 300ms. RMS is a traditional loudness measurement, which is a good first-order approximation of perceived loudness. This mode doesn’t apply K-weighting or channel weighting to the compressor’s detection circuitry, giving it a more traditional character.

RMS

True Peak

True Peak loudness types are similar to traditional peak measurements, but they are more accurate as they take into consideration inter-sample peaks. These measurements use a time interval equal to the configured block size (1ms by default). This mode is extremely responsive, making it suitable for very fast attack and release times.

True Peak

Peak

Peak loudness types are a standard peak circuit, operating on a time interval equal to the configured block size (1ms by default). This is another traditional compressor style measurement. Technically, this mode is even slightly more responsive than True Peak, but it is less accurate as it doesn’t take into consideration inter-sample peaks.

True Peak



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Dynamic types

In additional to the unique “Source → Target” mode, the compressor also supports a variety of dynamic types. The compressor can be configured to operate as a traditional downward compressor, upward compressor, downward expander, upware expander, or soft limiting. These modes can be selected using the drop-down menu above the “Dry/Wet” dial.



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Credits

This software was developed by APU Software, LLC and is available as VST (windows x64/x86, macOS universal), Audio Unit (macOS universal), Pro Tools (windows x64/x86, macOS universal), or Standalone Application. The software libraries below are utilized for portions of the software:

  • JUCE (cross-platform audio and user interface framework)
  • Boost (header-only algorithms)
  • libebur128 (loudness measurements)

Demo video song credits:

  • Annasara - A Lifetime Rolls By, licensed via Audiio.

VST compatible




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