In a signal transmission system for transmitting an analog signal, in which a billing signal is superposed on an audio signal, from a transmitting device to a receiving device, the transmitting device includes a separation unit configured to separate the audio signal from the analog signal, an AD conversion unit configured to perform AD conversion on the audio signal separated by the separation unit, a detection unit configured to detect the billing signal from the analog signal, a coding unit configured to encode the billing signal detected by the detection unit, and a transmission unit configured to transmit the audio signal subjected to the AD conversion by the AD conversion unit and the billing signal encoded by the coding unit to the receiving device, and the receiving device includes a reception unit configured to receive the audio signal and the billing signal transmitted by the transmission unit, a DA conversion unit configured to perform DA conversion on the audio signal received by the reception unit, a decoding unit configured to decode the billing signal received by the reception unit, a conversion unit configured to convert the billing signal decoded by the decoding unit into an analog wave, and a combination unit configured to combine the audio signal subjected to the DA conversion by the DA conversion unit and the analog wave.

In a signal transmission system for transmitting an analog signal, in which a billing signal is superposed on an audio signal, from a transmitting device to a receiving device, the transmitting device includes a separation unit configured to separate the audio signal from the analog signal, an AD conversion unit configured to perform AD conversion on the audio signal separated by the separation unit, a detection unit configured to detect the billing signal from the analog signal, a coding unit configured to encode the billing signal detected by the detection unit, and a transmission unit configured to transmit the audio signal subjected to the AD conversion by the AD conversion unit and the billing signal encoded by the coding unit to the receiving device, and the receiving device includes a reception unit configured to receive the audio signal and the billing signal transmitted by the transmission unit, a DA conversion unit configured to perform DA conversion on the audio signal received by the reception unit, a decoding unit configured to decode the billing signal received by the reception unit, a conversion unit configured to convert the billing signal decoded by the decoding unit into an analog wave, and a combination unit configured to combine the audio signal subjected to the DA conversion by the DA conversion unit and the analog wave.