An roll-off in cinema sound systems response above ~2kHz (to -18dB at 8kHz) to minimize noise in mono optical tracks. Some (many) transfers to home video of mono movies have neglected to add the Academy filter during transfer, giving many old movies an overbright and aggressive sound they were never intended to have. Some domestic A/V processors have an Academy filter option (Re-Eq), making them a must for old-movie buffs. Has been used since 1938.