B-chain and X-curve: tuning cinema sound

A large auditorium does not reproduce sound the way a mixing room does, and a speaker measured flat in the room sounds harsh and bright. The X-curve, standardised as SMPTE ST 202 and ISO 2969, is the target response the B-chain is equalised to: flat up to around 2 kHz, then rolling off gently towards the high frequencies, with adjustments for smaller rooms.

Films are mixed on stages tuned to the same curve. That is the whole point: if both ends follow it, what the mixer heard is what your audience hears.

Reference playback level is set by playing pink noise at a defined level through each screen channel and adjusting to a reference reading — a procedure in SMPTE RP 200. Most cinemas then run below the reference fader setting, because trailers and adverts are mixed louder than features and generate the "too loud" complaints.

The durable fix is a proper calibration plus a sensible playlist with different levels for pre-show and feature, rather than a manager turning the fader down on a Friday night.