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).