5.3 Modulation and demodulation The measurand, usually a low-frequency signal controlling the high frequency oscillation, is called modulating signal, the high-frequenc oscillation used for carrying the low-frequency signal is known as carrier, and the resulting signal from the modulation process, still a high-frequency oscillation, is known as modulated signal In time domain, modulation is a process in which a certain parameter of the carrier is varied with the modulating signal, while in frequency domain, it is a process of phase-shifting5.3 Modulation and demodulation The measurand, usually a low-frequency signal controlling the high frequency oscillation, is called modulating signal, the high-frequency oscillation used for carrying the low-frequency signal is known as carrier, and the resulting signal from the modulation process, still a high-frequency oscillation, is known as modulated signal. In time domain, modulation is a process in which a certain parameter of the carrier is varied with the modulating signal, while in frequency domain, it is a process of phase-shifting