Which of the following is one function of most sound card interfaces in a station operating computer-based digital modes?

A dedicated sound card interface often does more than just pass audio back and forth. One of its most important secondary functions is to handle the Push-To-Talk (PTT) keying, which allows the computer to automatically switch the transceiver from receive to transmit mode when data is ready to be sent. While the software on the computer translates digital signals into alphanumeric characters on your screen, the physical sound card interface hardware itself does not do this translation. Modulating received signals or displaying frequencies are also incorrect, as those are functions of the transceiver, demodulator, or CAT control software.