Abstract: A binaural sound recording and reproduction system which utilizes a recording mannequin equipped with an electroacoustic model of the human auditory tract to thereby record the sound pressure which would be incident on a listener's eardrum and also utilizes a headset with in-ear transducers or receivers which exhibit a flat frequency response as measured at the listener's eardrums is described. The receiver units utilize acoustic impedance matching to the listener's ear canal to effect the flat frequency response characteristic. An electrical equalizer circuit to facilitate the use of the subject in-ear receivers with conventionally recorded sound is also disclosed.

Abstract: 1. In a privacy system in which the signals are divided into fragments on a time basis and the different fragments are delayed in transmission by different amounts to afford privacy, a timing means having a timing cycle divided into several periods, a relay individual to each period and individually operated during its respective period by said timing means, a plurality of delay devices to introduce delay into said signals, means controlled by said timing means to select a delay device for each timing period, and means jointly controlled by said relays and selecting means to operate the selected devices.