K-weighting is the frequency-weighting curve at the heart of modern loudness measurement, defined in ITU-R BS.1770. Before a meter integrates a signal into a loudness number it passes it through this two-stage filter: a high-shelf boost that approximates the acoustic effect of the head, plus a high-pass that rolls off the lowest frequencies the ear weights less. The result tracks perceived loudness far better than a flat reading, and it is the 'K' in LKFS. Every loudness target you meet — EBU R128's -23, ATSC's -24, streaming's about -14 — is a K-weighted, gated measurement. It is deliberately simple and standardized so every compliant meter agrees.
