Method of Amplitude Modulating a Message Signal in the Audible Frequency Range Onto a Carrier Signal in the Ultrasonic Frequency Range

摘要

This invention relates to signal processing and to acoustics. The invention provides a method of amplitude modulating a message signal ( 12 ) in the audible frequency range of a human onto a carrier signal ( 14 ) in the ultrasonic frequency range, the method including generating an amplitude modulated signal ( 20.1 ) having a constant envelope on one side ( 72 ). The invention extends also to a method of amplitude modulating a message signal ( 12 ) in the audible frequency range of a human onto a carrier signal ( 14 ) in the ultrasonic frequency range, the method including generating an amplitude modulated signal ( 20.2 ) having a constant level ( 33 ) defined successively by an upper and lower envelope of the amplitude modulated signal ( 20.2 ). The invention also extends to related amplitude modulators ( 10 ) and ( 110 ) and also to a related acoustic system ( 50 ).