APU Software

APU Loudness Limiter

LUFS, True Peak, RMS, Peak

The APU Loudness Limiter is a real-time limiter designed to support multiple loudness types simultaneously. The limiter can be configured to use LUFS, True Peak, RMS, and/or Peak loudness types. This allows you to target multiple requirements simultaneously, such as a specific LUFS target and a specific True Peak target. Internally, the ballistics of the limiter are adjusted to accommodate the different loudness type limiter settings.



Note: If you have already purchased the optimizer and/or compressor and would like to receive a discount price for the limiter, please reach out using the "Contact the Developer" link on this site.

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 limiter is its support for a variety of loudness types. The limiter’s detection circuitry can be configured to use either LUFS and/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 limiter’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. 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

Integrated

Integrated is an infinite duration LUFS measurement. K-weighting and channel weighting are applied as with momentary, as well as both relative and absolute gating. This loudness type can be useful for continuously wrangling the audio’s integrated loudness toward a specific target.

Integrated LUFS

RMS

RMS loudness types use a rolling time interval of 150ms by default, which can be adjusted. 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 limiter’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 prevents clipping inter-sample peaks, which can be useful for mastering.

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 limiter 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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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:

Demo video song credits:


VST compatible ASIO compatible



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