What signals are used in a computer-radio interface for digital mode operation?

To operate digital modes like FT8 or PSK31, a computer acts as a modem, translating digital data into audio tones and vice-versa. Therefore, the computer and radio must exchange specific baseband signals to function together. The computer must hear what the radio receives (receive audio), send generated tones to the radio to be broadcast (transmit audio), and tell the radio exactly when to transmit (transmitter keying or PTT). Distractors mentioning RF power, antenna connections, or GPS are incorrect because the computer-radio interface only handles audio routing and basic transmit/receive control, not the actual radio frequency transmission or geographic location.