Abstract: A ground proximity warning system used by aircraft when unsafe flight configurations defined by specified flight warning mode envelopes are detected. The invention provides that alarm generation signals are not immediately given, but instead the continuing flight of the aircraft is monitored by an alarm filtering system. The filtering system uses independently variable maximum and minimum threshold levels, and filtering constants which can be incremented and or decremented as functions of the flight location of the aircraft and the specific warning mode envelope for suppressing false or unnecessary alarm generation. The filtering parameters may be varied independently for each flight warning mode. In addition, a priority-ordered series of audio warnings are provided so that warnings once started are completed in the absence of higher priority warnings, even if the warning conditions cease to exist.

Abstract: A speech transmission system employing a semi-vocoder comprising a spectral analyzer and a spectral synthesizer for the upper frequency range of the speech signal. The speech signal in the low frequency range base band is transmitted by using delta modulation and the delta-modulated base band signal is used directly in the receiver as a voice excitation signal for the spectral synthesizer.