APU Software Loudness Contour (Digital product)

APU Loudness Contour — Real-Time Equal-Loudness Filtering

APU Loudness Contour is a plug-in that applies psychoacoustic frequency curves to audio, compensating for how human hearing perceives less bass and treble at low volumes. It runs as VST, AU, AAX, or a standalone app on macOS and Windows. Each curve is normalized to 0 dB at 1 kHz for easy A/B comparison against your dry signal.

Seven Curve Types, Full Control

Choose from ISO 226 (2003 and 2023), Fletcher-Munson, K-weighting, A/C-weighting, ECMA-418, and ITU-R 468. The contour weight scales the curve from flat to full, or inverts it with negative values. For ISO 226 and Fletcher-Munson, a reference SPL control selects the phon level across a 20–120 range, with an Adaptive SPL option that adjusts automatically as input loudness changes.

For Producers Mixing at Any Volume

This plug-in is the right choice for producers and engineers who want to maintain spectral balance when mixing quietly, or for shaping synths and buses with hearing-based curves. A 30-day trial lets you explore loudness-based EQ risk-free.