A transmitter includes a signal input terminal, multiple loading units and a communication port. The signal input terminal receives a digital video-audio signal, which comprises multiple digital differential signals and multiple single-end/low frequency signals. The loading units respectively load the corresponding single-end/low frequency signals to the digital differential signals to obtain multiple differential mixed signals. A frequency of the digital differential signals is higher than a frequency of the corresponding single-end/low frequency signals. The communication port outputs the differential mixed signals to a receiver via a network cable.