Adrian McCarthy a reader of the website BoingBoing has alerted them to the fact that Paramount are silencing portions of the soundtrack to Indiana Jones and the Kingdom of the Crystal Skull as an effort to deter and detect piracy.
This is an audio form of Coded Anti-Piracy which typically is a distinguishing patterns of dots printed in several frames of a film print.
However the effect shouldn’t complete silence instead the system should switch from digital to analog sound and shouldn’t be noticeable by the majority of the audience.
Film-Tech forums projectionists talk about this. Digital drop out to analog and if the sound output levels of the two hasn’t been matched there will be an audible difference and in particularly shoddy set ups with no switch to analog there will be a complete silence until the digital system reacquires the track.