X curve

This is the name for an equalization curve for the cinematic B-chain (amplifier, loudspeakers and room). This curve followed the N-curve (see this) to be an extended curve) providing a wider frequency response for the reproduction of film sound in the cinema. It became a standard (ISO 2969) that has existed since being introduced in the 1970s. Nowadays, other standards and practices have taken over, following the immersive formats.