A communication system has a communication controller for multiplexing and transmitting a power supply voltage and an audio signal to be played back by a plurality of channels, and a plurality of communication adapters which start in response to reception of the multiplexed/transmitted power supply voltage, and play back the audio signal using a playback device. The communication controller includes an audio data modulation circuit configured to modulate audio data by shifting, based on a first modulation ratio, a modulation carrier clock for modulating the audio data and a data transmission rate for transmitting the audio data in order to set a command transmission frequency bandwidth, and a command data modulation circuit configured to modulate command data by shifting, based on a second modulation ratio, a modulation carrier clock for modulating the command data and a data transmission rate for transmitting the command data in the command transmission frequency bandwidth.