Description

APU Loudness Contour is a real-time equal-loudness filter that offers precise control over a wide range of perceptual 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 weight parameter, allowing you to scale the frequency response in both positive and negative directions. A weight of 0% results in a flat response, while negative weights invert the contour.

For Phon-dependent contours like ISO 226 and Fletcher-Munson, a reference SPL parameter allows you to select the desired phon level from 20-120 dB SPL. With Adaptive SPL enabled, this reference level automatically adjusts based on the incoming signal’s loudness level, allowing the contour to dynamically respond to program material.

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

A comprehensive real-time spectrum analyzer is included, featuring configurable FFT sizes, window types, bucket widths, and time averaging. Frequency visualization can be switched between linear, logarithmic, or musical note scales, with auto-zoom and custom dB range options.

Features

• Adaptive SPL behavior
• Positive or negative contour weighting
• Linear-phase and minimum-phase filtering
• Pink-noise LUFS makeup gain
• Built-in spectrum analyzer
• ISO 226:2023 and ISO 226:2003 equal-loudness contours
• Fletcher-Munson, K, A, C, ECMA-418, and ITU-R 468 contours

Tech Specs