APU Software

Loudness Compressor

Shape dynamics with loudness-based compression

Sale price $30.00 one-time · Regular price $40.00

APU Loudness Compressor helps bring uneven vocals, bass parts, and mixes under control. Use compression to reduce differences in level, or expansion to give a track more dynamic range. With LUFS detection, gain changes follow measured loudness rather than just signal peaks. RMS, Peak, and True Peak detection are also available.

I started APU Software because I wanted a compressor with LUFS built directly into its detector. The Loudness Compressor grew out of that idea, and I’ve continued adding features since then.

For a closer look at how it sounds and works, here are two independent reviews:

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

Loudness Types

Choose the measurement that drives the compressor: LUFS, RMS, Peak, or True Peak. Link channels to process them together, or split them for independent processing.

Momentary

Momentary measures loudness over a 400 ms window with K-weighting and channel weighting. It follows shorter changes in level and is the compressor’s default measurement.

Short-Term

Short-Term measures loudness over a 3-second window, following longer changes in level. It uses the same K-weighting and channel weighting as Momentary.

Integrated

Integrated measures loudness over the measurement run, using K-weighting, channel weighting, and relative and absolute gating. Use it when you want compression to follow the accumulated loudness measurement.

RMS

RMS measures signal level over an adjustable window, set to 150 ms by default. It does not apply K-weighting or channel weighting.

True Peak

True Peak estimates peaks between samples as well as sample peaks. It uses the configured block interval, which is 1 ms by default, for a fast detector response.

Peak

Peak measures sample peaks over the configured block interval, which is 1 ms by default. It does not estimate peaks between samples.

Alternate Weighting

Alternate weighting curves change how much each frequency contributes to the detector. Use them to adjust how strongly bass, midrange, or high-frequency content drives the compressor. Measurements with alternate weighting are no longer standard LUFS measurements.

The screenshots below show the curves in Loudness Contour. The compressor applies them as zero-latency IIR filters in the detector path.

ECMA-418

ECMA-418 uses the outer- and middle-ear weighting curve from the ECMA-418-2 hearing model. It provides an alternative to K-weighting; it does not apply the standard’s full loudness model.

ITU-R 468

ITU-R 468 emphasizes the upper midrange, making the detector more sensitive to sibilance and other high-frequency content. Gain changes still affect the whole signal.

A-weighting

A-weighting reduces the influence of low frequencies. Use it when you want bass to contribute less to compression.

C-weighting

C-weighting is flatter than A-weighting and retains more low-frequency energy in the detector.

Detector EQ

Detector EQ shapes the signal used for loudness detection. Emphasize a frequency range to make it drive more of the compression, or reduce low frequencies so rumble has less influence.

Note: The EQ isn't applied directly to the output, but it changes the compressor's gain response. Enable detector EQ monitor to hear the filtered detector signal.