What is the generic name of the device that is used with a special, digital phone line to transmit high-quality stereo audio?

The device that is used with a special, digital phone line to transmit high-quality stereo audio is known as an ISDN codec. ISDN stands for Integrated Services Digital Network, which is a set of communication standards for simultaneous digital transmission of voice, data, and video over the traditional circuits of the public switched telephone network.

An ISDN codec converts audio into a digital format that can be transmitted over an ISDN line, ensuring high fidelity and low latency, which are essential for broadcasting and professional audio applications. This makes it particularly valuable for applications where sound quality is critical, such as radio broadcasting or live music events.

While an audio interface and digital audio mixer are important for managing audio input and output, they do not specifically facilitate transmission over ISDN lines. Similarly, a wireless transmitter is used for sending audio signals without cables but does not utilize digital phone lines for transmission. The ISDN codec's specific role in this context is why it is the correct answer.