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.

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.

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.

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.

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.

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.

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.

Homepage https://apu.software/limiter/#loudnessTypes