APU Software Loudness Contour 4.3.6

APU Loudness Contour is a real-time equal loudness filter that provides precise control over a wide range of perceived loudness contours, including ISO 226 (2003 & 2023), Fletcher-Munson, K-weighting, A/C-weighting, ECMA-418, and ITU-R 468.

Each contour is normalized to 0 dB at 1 kHz and includes a dedicated contour weighting parameter application, allowing you to adjust the frequency response in both the positive and negative directions. 0% weighting gives a flat response, while negative weighting inverts the contour. The ISO 226 and Fletcher-Munson curves support variable reference levels from 20 dB SPL to 120 dB SPL, with smooth interpolation between negative curves.

The plugin supports both linear and minimum phase filter types. Built-in gain compensation is provided for each contour and reference level, calibrated using pink noise LUFS measurements. When enabled, the offset gain offsets the entire contour response by the corresponding gain. Additional output gain is available for manual fine-tuning.

Includes a comprehensive real-time spectrum analyzer, with configurable FFT sizes, window types, bucket widths, and time averaging. The frequency display can be switched between linear, logarithmic or pitch scale, with auto-zoom and dB range customization.